ebiten: Add EvenOdd to DrawTrianglesOptions and DrawShaderTrianglesOptions

Updates #844
Closes #1684

examples/vector/main.go

@@ -19,6 +19,7 @@ package main
 
 import (
 	"fmt"
+	"image"
 	"image/color"
 	"log"
 	"math"
@@ -28,6 +29,15 @@ import (
 	"github.com/hajimehoshi/ebiten/v2/vector"
 )
 
+var (
+	emptyImage    = ebiten.NewImage(3, 3)
+	emptySubImage = emptyImage.SubImage(image.Rect(1, 1, 2, 2)).(*ebiten.Image)
+)
+
+func init() {
+	emptyImage.Fill(color.White)
+}
+
 const (
 	screenWidth  = 640
 	screenHeight = 480
@@ -99,10 +109,18 @@ func drawEbitenText(screen *ebiten.Image) {
 	path.LineTo(320, 55)
 	path.LineTo(290, 20)
 
-	op := &vector.FillOptions{
-		Color: color.RGBA{0xdb, 0x56, 0x20, 0xff},
+	op := &ebiten.DrawTrianglesOptions{
+		EvenOdd: true,
 	}
-	path.Fill(screen, op)
+	vs, is := path.AppendVerticesAndIndices(nil, nil)
+	for i := range vs {
+		vs[i].SrcX = 1
+		vs[i].SrcY = 1
+		vs[i].ColorR = 0xdb / float32(0xff)
+		vs[i].ColorG = 0x56 / float32(0xff)
+		vs[i].ColorB = 0x20 / float32(0xff)
+	}
+	screen.DrawTriangles(vs, is, emptySubImage, op)
 }
 
 func drawEbitenLogo(screen *ebiten.Image, x, y int) {
@@ -131,10 +149,18 @@ func drawEbitenLogo(screen *ebiten.Image, x, y int) {
 	path.LineTo(xf+unit, yf+3*unit)
 	path.LineTo(xf+unit, yf+4*unit)
 
-	op := &vector.FillOptions{
-		Color: color.RGBA{0xdb, 0x56, 0x20, 0xff},
+	op := &ebiten.DrawTrianglesOptions{
+		EvenOdd: true,
 	}
-	path.Fill(screen, op)
+	vs, is := path.AppendVerticesAndIndices(nil, nil)
+	for i := range vs {
+		vs[i].SrcX = 1
+		vs[i].SrcY = 1
+		vs[i].ColorR = 0xdb / float32(0xff)
+		vs[i].ColorG = 0x56 / float32(0xff)
+		vs[i].ColorB = 0x20 / float32(0xff)
+	}
+	screen.DrawTriangles(vs, is, emptySubImage, op)
 }
 
 func maxCounter(index int) int {
@@ -166,10 +192,18 @@ func drawWave(screen *ebiten.Image, counter int) {
 	path.LineTo(screenWidth, screenHeight)
 	path.LineTo(0, screenHeight)
 
-	op := &vector.FillOptions{
-		Color: color.RGBA{0x33, 0x66, 0xff, 0xff},
+	op := &ebiten.DrawTrianglesOptions{
+		EvenOdd: true,
 	}
-	path.Fill(screen, op)
+	vs, is := path.AppendVerticesAndIndices(nil, nil)
+	for i := range vs {
+		vs[i].SrcX = 1
+		vs[i].SrcY = 1
+		vs[i].ColorR = 0x33 / float32(0xff)
+		vs[i].ColorG = 0x66 / float32(0xff)
+		vs[i].ColorB = 0xff / float32(0xff)
+	}
+	screen.DrawTriangles(vs, is, emptySubImage, op)
 }
 
 type Game struct {

image.go

@@ -213,7 +213,7 @@ func (i *Image) DrawImage(img *Image, options *DrawImageOptions) {
 	is := graphics.QuadIndices()
 
 	srcs := [graphics.ShaderImageNum]*mipmap.Mipmap{img.mipmap}
-	i.mipmap.DrawTriangles(srcs, vs, is, options.ColorM.impl, mode, filter, driver.AddressUnsafe, dstRegion, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil, canSkipMipmap(options.GeoM, filter))
+	i.mipmap.DrawTriangles(srcs, vs, is, options.ColorM.impl, mode, filter, driver.AddressUnsafe, dstRegion, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil, false, canSkipMipmap(options.GeoM, filter))
 }
 
 // Vertex represents a vertex passed to DrawTriangles.
@@ -271,6 +271,19 @@ type DrawTrianglesOptions struct {
 	// Address is a sampler address mode.
 	// The default (zero) value is AddressUnsafe.
 	Address Address
+
+	// EvenOdd represents whether the even-odd rule is applied or not.
+	//
+	// If EvenOdd is true, triangles are rendered based on the even-odd rule. If false, triangles are rendered without condition.
+	// Whether overlapped regions by multiple triangles is rendered or not depends on the number of the overlapping:
+	// if and only if the number is odd, the region is rendered.
+	//
+	// EvenOdd is useful when you want to render a complex polygon.
+	// A complex polygon is a non-convex polygon like a concave polygon, a polygon with holes, or a self-intersecting polygon.
+	// See examples/vector for actual usages.
+	//
+	// The default value is false.
+	EvenOdd bool
 }
 
 // MaxIndicesNum is the maximum number of indices for DrawTriangles.
@@ -349,7 +362,7 @@ func (i *Image) DrawTriangles(vertices []Vertex, indices []uint16, img *Image, o
 
 	srcs := [graphics.ShaderImageNum]*mipmap.Mipmap{img.mipmap}
 
-	i.mipmap.DrawTriangles(srcs, vs, is, options.ColorM.impl, mode, filter, address, dstRegion, sr, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil, false)
+	i.mipmap.DrawTriangles(srcs, vs, is, options.ColorM.impl, mode, filter, address, dstRegion, sr, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil, options.EvenOdd, false)
 }
 
 // DrawTrianglesShaderOptions represents options for DrawTrianglesShader.
@@ -371,6 +384,19 @@ type DrawTrianglesShaderOptions struct {
 	// Images is a set of the source images.
 	// All the image must be the same size.
 	Images [4]*Image
+
+	// EvenOdd represents whether the even-odd rule is applied or not.
+	//
+	// If EvenOdd is true, triangles are rendered based on the even-odd rule. If false, triangles are rendered without condition.
+	// Whether overlapped regions by multiple triangles is rendered or not depends on the number of the overlapping:
+	// if and only if the number is odd, the region is rendered.
+	//
+	// EvenOdd is useful when you want to render a complex polygon.
+	// A complex polygon is a non-convex polygon like a concave polygon, a polygon with holes, or a self-intersecting polygon.
+	// See examples/vector for actual usages.
+	//
+	// The default value is false.
+	EvenOdd bool
 }
 
 func init() {
@@ -485,7 +511,7 @@ func (i *Image) DrawTrianglesShader(vertices []Vertex, indices []uint16, shader
 	}
 
 	us := shader.convertUniforms(options.Uniforms)
-	i.mipmap.DrawTriangles(imgs, vs, is, nil, mode, driver.FilterNearest, driver.AddressUnsafe, dstRegion, sr, offsets, shader.shader, us, false)
+	i.mipmap.DrawTriangles(imgs, vs, is, nil, mode, driver.FilterNearest, driver.AddressUnsafe, dstRegion, sr, offsets, shader.shader, us, options.EvenOdd, false)
 }
 
 // DrawRectShaderOptions represents options for DrawRectShader.
@@ -597,7 +623,7 @@ func (i *Image) DrawRectShader(width, height int, shader *Shader, options *DrawR
 	}
 
 	us := shader.convertUniforms(options.Uniforms)
-	i.mipmap.DrawTriangles(imgs, vs, is, nil, mode, driver.FilterNearest, driver.AddressUnsafe, dstRegion, sr, offsets, shader.shader, us, canSkipMipmap(options.GeoM, driver.FilterNearest))
+	i.mipmap.DrawTriangles(imgs, vs, is, nil, mode, driver.FilterNearest, driver.AddressUnsafe, dstRegion, sr, offsets, shader.shader, us, false, canSkipMipmap(options.GeoM, driver.FilterNearest))
 }
 
 // SubImage returns an image representing the portion of the image p visible through r.

internal/atlas/image.go

@@ -298,7 +298,7 @@ func (i *Image) ensureIsolated() {
 		Width:  float32(w - 2*paddingSize),
 		Height: float32(h - 2*paddingSize),
 	}
-	newImg.DrawTriangles(srcs, offsets, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dstRegion, driver.Region{}, nil, nil)
+	newImg.DrawTriangles(srcs, offsets, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dstRegion, driver.Region{}, nil, nil, false)
 
 	i.dispose(false)
 	i.backend = &backend{
@@ -354,7 +354,7 @@ func (i *Image) putOnAtlas() error {
 			Width:  w,
 			Height: h,
 		}
-		newI.drawTriangles([graphics.ShaderImageNum]*Image{i}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil, true)
+		newI.drawTriangles([graphics.ShaderImageNum]*Image{i}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil, false, true)
 	}
 
 	newI.moveTo(i)
@@ -402,13 +402,13 @@ func (i *Image) processSrc(src *Image) {
 //   5: Color G
 //   6: Color B
 //   7: Color Y
-func (i *Image) DrawTriangles(srcs [graphics.ShaderImageNum]*Image, vertices []float32, indices []uint16, colorm *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, subimageOffsets [graphics.ShaderImageNum - 1][2]float32, shader *Shader, uniforms []interface{}) {
+func (i *Image) DrawTriangles(srcs [graphics.ShaderImageNum]*Image, vertices []float32, indices []uint16, colorm *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, subimageOffsets [graphics.ShaderImageNum - 1][2]float32, shader *Shader, uniforms []interface{}, evenOdd bool) {
 	backendsM.Lock()
 	defer backendsM.Unlock()
-	i.drawTriangles(srcs, vertices, indices, colorm, mode, filter, address, dstRegion, srcRegion, subimageOffsets, shader, uniforms, false)
+	i.drawTriangles(srcs, vertices, indices, colorm, mode, filter, address, dstRegion, srcRegion, subimageOffsets, shader, uniforms, evenOdd, false)
 }
 
-func (i *Image) drawTriangles(srcs [graphics.ShaderImageNum]*Image, vertices []float32, indices []uint16, colorm *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, subimageOffsets [graphics.ShaderImageNum - 1][2]float32, shader *Shader, uniforms []interface{}, keepOnAtlas bool) {
+func (i *Image) drawTriangles(srcs [graphics.ShaderImageNum]*Image, vertices []float32, indices []uint16, colorm *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, subimageOffsets [graphics.ShaderImageNum - 1][2]float32, shader *Shader, uniforms []interface{}, evenOdd bool, keepOnAtlas bool) {
 	if i.disposed {
 		panic("atlas: the drawing target image must not be disposed (DrawTriangles)")
 	}
@@ -487,7 +487,7 @@ func (i *Image) drawTriangles(srcs [graphics.ShaderImageNum]*Image, vertices []f
 		}
 	}
 
-	i.backend.restorable.DrawTriangles(imgs, offsets, vertices, indices, colorm, mode, filter, address, dstRegion, srcRegion, s, uniforms)
+	i.backend.restorable.DrawTriangles(imgs, offsets, vertices, indices, colorm, mode, filter, address, dstRegion, srcRegion, s, uniforms, evenOdd)
 
 	for _, src := range srcs {
 		if src == nil {

internal/atlas/image_test.go

@@ -102,7 +102,7 @@ func TestEnsureIsolated(t *testing.T) {
 		Width:  size,
 		Height: size,
 	}
-	img4.DrawTriangles([graphics.ShaderImageNum]*Image{img3}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil)
+	img4.DrawTriangles([graphics.ShaderImageNum]*Image{img3}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil, false)
 	want := false
 	if got := img4.IsOnAtlasForTesting(); got != want {
 		t.Errorf("got: %v, want: %v", got, want)
@@ -132,7 +132,7 @@ func TestEnsureIsolated(t *testing.T) {
 
 	// Check further drawing doesn't cause panic.
 	// This bug was fixed by 03dcd948.
-	img4.DrawTriangles([graphics.ShaderImageNum]*Image{img3}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil)
+	img4.DrawTriangles([graphics.ShaderImageNum]*Image{img3}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil, false)
 }
 
 func TestReputOnAtlas(t *testing.T) {
@@ -179,7 +179,7 @@ func TestReputOnAtlas(t *testing.T) {
 		Width:  size,
 		Height: size,
 	}
-	img1.DrawTriangles([graphics.ShaderImageNum]*Image{img2}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil)
+	img1.DrawTriangles([graphics.ShaderImageNum]*Image{img2}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil, false)
 	if got, want := img1.IsOnAtlasForTesting(), false; got != want {
 		t.Errorf("got: %v, want: %v", got, want)
 	}
@@ -191,7 +191,7 @@ func TestReputOnAtlas(t *testing.T) {
 		if err := PutImagesOnAtlasForTesting(); err != nil {
 			t.Fatal(err)
 		}
-		img0.DrawTriangles([graphics.ShaderImageNum]*Image{img1}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil)
+		img0.DrawTriangles([graphics.ShaderImageNum]*Image{img1}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil, false)
 		if got, want := img1.IsOnAtlasForTesting(), false; got != want {
 			t.Errorf("got: %v, want: %v", got, want)
 		}
@@ -219,7 +219,7 @@ func TestReputOnAtlas(t *testing.T) {
 	}
 
 	// img1 is on an atlas again.
-	img0.DrawTriangles([graphics.ShaderImageNum]*Image{img1}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil)
+	img0.DrawTriangles([graphics.ShaderImageNum]*Image{img1}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil, false)
 	if got, want := img1.IsOnAtlasForTesting(), true; got != want {
 		t.Errorf("got: %v, want: %v", got, want)
 	}
@@ -243,7 +243,7 @@ func TestReputOnAtlas(t *testing.T) {
 	}
 
 	// Use img1 as a render target again.
-	img1.DrawTriangles([graphics.ShaderImageNum]*Image{img2}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil)
+	img1.DrawTriangles([graphics.ShaderImageNum]*Image{img2}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil, false)
 	if got, want := img1.IsOnAtlasForTesting(), false; got != want {
 		t.Errorf("got: %v, want: %v", got, want)
 	}
@@ -255,7 +255,7 @@ func TestReputOnAtlas(t *testing.T) {
 			t.Fatal(err)
 		}
 		img1.ReplacePixels(make([]byte, 4*size*size))
-		img0.DrawTriangles([graphics.ShaderImageNum]*Image{img1}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil)
+		img0.DrawTriangles([graphics.ShaderImageNum]*Image{img1}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil, false)
 		if got, want := img1.IsOnAtlasForTesting(), false; got != want {
 			t.Errorf("got: %v, want: %v", got, want)
 		}
@@ -265,7 +265,7 @@ func TestReputOnAtlas(t *testing.T) {
 	}
 
 	// img1 is not on an atlas due to ReplacePixels.
-	img0.DrawTriangles([graphics.ShaderImageNum]*Image{img1}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil)
+	img0.DrawTriangles([graphics.ShaderImageNum]*Image{img1}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil, false)
 	if got, want := img1.IsOnAtlasForTesting(), false; got != want {
 		t.Errorf("got: %v, want: %v", got, want)
 	}
@@ -275,7 +275,7 @@ func TestReputOnAtlas(t *testing.T) {
 		if err := PutImagesOnAtlasForTesting(); err != nil {
 			t.Fatal(err)
 		}
-		img0.DrawTriangles([graphics.ShaderImageNum]*Image{img3}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil)
+		img0.DrawTriangles([graphics.ShaderImageNum]*Image{img3}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil, false)
 		if got, want := img3.IsOnAtlasForTesting(), false; got != want {
 			t.Errorf("got: %v, want: %v", got, want)
 		}
@@ -375,7 +375,7 @@ func TestReplacePixelsAfterDrawTriangles(t *testing.T) {
 		Width:  w,
 		Height: h,
 	}
-	dst.DrawTriangles([graphics.ShaderImageNum]*Image{src}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil)
+	dst.DrawTriangles([graphics.ShaderImageNum]*Image{src}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil, false)
 	dst.ReplacePixels(pix)
 
 	pix, err := dst.Pixels(0, 0, w, h)
@@ -423,7 +423,7 @@ func TestSmallImages(t *testing.T) {
 		Width:  w,
 		Height: h,
 	}
-	dst.DrawTriangles([graphics.ShaderImageNum]*Image{src}, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil)
+	dst.DrawTriangles([graphics.ShaderImageNum]*Image{src}, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil, false)
 
 	pix, err := dst.Pixels(0, 0, w, h)
 	if err != nil {
@@ -471,7 +471,7 @@ func TestLongImages(t *testing.T) {
 		Width:  dstW,
 		Height: dstH,
 	}
-	dst.DrawTriangles([graphics.ShaderImageNum]*Image{src}, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil)
+	dst.DrawTriangles([graphics.ShaderImageNum]*Image{src}, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil, false)
 
 	pix, err := dst.Pixels(0, 0, dstW, dstH)
 	if err != nil {
@@ -559,7 +559,7 @@ func TestDisposedAndReputOnAtlas(t *testing.T) {
 		Width:  size,
 		Height: size,
 	}
-	src.DrawTriangles([graphics.ShaderImageNum]*Image{src2}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil)
+	src.DrawTriangles([graphics.ShaderImageNum]*Image{src2}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil, false)
 	if got, want := src.IsOnAtlasForTesting(), false; got != want {
 		t.Errorf("got: %v, want: %v", got, want)
 	}
@@ -569,7 +569,7 @@ func TestDisposedAndReputOnAtlas(t *testing.T) {
 		if err := PutImagesOnAtlasForTesting(); err != nil {
 			t.Fatal(err)
 		}
-		dst.DrawTriangles([graphics.ShaderImageNum]*Image{src}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil)
+		dst.DrawTriangles([graphics.ShaderImageNum]*Image{src}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil, false)
 		if got, want := src.IsOnAtlasForTesting(), false; got != want {
 			t.Errorf("got: %v, want: %v", got, want)
 		}
@@ -609,7 +609,7 @@ func TestImageIsNotReputOnAtlasWithoutUsingAsSource(t *testing.T) {
 	}
 
 	// Use src2 as a rendering target, and make src2 an independent image.
-	src2.DrawTriangles([graphics.ShaderImageNum]*Image{src}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil)
+	src2.DrawTriangles([graphics.ShaderImageNum]*Image{src}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil, false)
 	if got, want := src2.IsOnAtlasForTesting(), false; got != want {
 		t.Errorf("got: %v, want: %v", got, want)
 	}
@@ -630,7 +630,7 @@ func TestImageIsNotReputOnAtlasWithoutUsingAsSource(t *testing.T) {
 		if err := PutImagesOnAtlasForTesting(); err != nil {
 			t.Fatal(err)
 		}
-		dst.DrawTriangles([graphics.ShaderImageNum]*Image{src2}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil)
+		dst.DrawTriangles([graphics.ShaderImageNum]*Image{src2}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil, false)
 		if got, want := src2.IsOnAtlasForTesting(), false; got != want {
 			t.Errorf("got: %v, want: %v", got, want)
 		}

internal/buffered/image.go

@@ -202,7 +202,7 @@ func (i *Image) replacePendingPixels(pix []byte, x, y, width, height int) {
 // DrawTriangles draws the src image with the given vertices.
 //
 // Copying vertices and indices is the caller's responsibility.
-func (i *Image) DrawTriangles(srcs [graphics.ShaderImageNum]*Image, vertices []float32, indices []uint16, colorm *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, subimageOffsets [graphics.ShaderImageNum - 1][2]float32, shader *Shader, uniforms []interface{}) {
+func (i *Image) DrawTriangles(srcs [graphics.ShaderImageNum]*Image, vertices []float32, indices []uint16, colorm *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, subimageOffsets [graphics.ShaderImageNum - 1][2]float32, shader *Shader, uniforms []interface{}, evenOdd bool) {
 	for _, src := range srcs {
 		if i == src {
 			panic("buffered: Image.DrawTriangles: source images must be different from the receiver")
@@ -212,7 +212,7 @@ func (i *Image) DrawTriangles(srcs [graphics.ShaderImageNum]*Image, vertices []f
 	if maybeCanAddDelayedCommand() {
 		if tryAddDelayedCommand(func() error {
 			// Arguments are not copied. Copying is the caller's responsibility.
-			i.DrawTriangles(srcs, vertices, indices, colorm, mode, filter, address, dstRegion, srcRegion, subimageOffsets, shader, uniforms)
+			i.DrawTriangles(srcs, vertices, indices, colorm, mode, filter, address, dstRegion, srcRegion, subimageOffsets, shader, uniforms, evenOdd)
 			return nil
 		}) {
 			return
@@ -238,7 +238,7 @@ func (i *Image) DrawTriangles(srcs [graphics.ShaderImageNum]*Image, vertices []f
 	}
 	i.resolvePendingPixels(false)
 
-	i.img.DrawTriangles(imgs, vertices, indices, colorm, mode, filter, address, dstRegion, srcRegion, subimageOffsets, s, uniforms)
+	i.img.DrawTriangles(imgs, vertices, indices, colorm, mode, filter, address, dstRegion, srcRegion, subimageOffsets, s, uniforms, evenOdd)
 	i.invalidatePendingPixels()
 }
 

internal/driver/graphics.go

@@ -57,7 +57,7 @@ type Graphics interface {
 	//
 	//   * float32
 	//   * []float32
-	DrawTriangles(dst ImageID, srcs [graphics.ShaderImageNum]ImageID, offsets [graphics.ShaderImageNum - 1][2]float32, shader ShaderID, indexLen int, indexOffset int, mode CompositeMode, colorM *affine.ColorM, filter Filter, address Address, dstRegion, srcRegion Region, uniforms []interface{}) error
+	DrawTriangles(dst ImageID, srcs [graphics.ShaderImageNum]ImageID, offsets [graphics.ShaderImageNum - 1][2]float32, shader ShaderID, indexLen int, indexOffset int, mode CompositeMode, colorM *affine.ColorM, filter Filter, address Address, dstRegion, srcRegion Region, uniforms []interface{}, evenOdd bool) error
 }
 
 // GraphicsNotReady represents that the graphics driver is not ready for recovering from the context lost.

internal/graphicscommand/command.go

@@ -55,7 +55,7 @@ type command interface {
 	NumIndices() int
 	AddNumVertices(n int)
 	AddNumIndices(n int)
-	CanMergeWithDrawTrianglesCommand(dst *Image, src [graphics.ShaderImageNum]*Image, color *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, shader *Shader) bool
+	CanMergeWithDrawTrianglesCommand(dst *Image, src [graphics.ShaderImageNum]*Image, color *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, shader *Shader, evenOdd bool) bool
 }
 
 type size struct {
@@ -133,7 +133,7 @@ func (q *commandQueue) appendIndices(indices []uint16, offset uint16) {
 }
 
 // EnqueueDrawTrianglesCommand enqueues a drawing-image command.
-func (q *commandQueue) EnqueueDrawTrianglesCommand(dst *Image, srcs [graphics.ShaderImageNum]*Image, offsets [graphics.ShaderImageNum - 1][2]float32, vertices []float32, indices []uint16, color *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, shader *Shader, uniforms []interface{}) {
+func (q *commandQueue) EnqueueDrawTrianglesCommand(dst *Image, srcs [graphics.ShaderImageNum]*Image, offsets [graphics.ShaderImageNum - 1][2]float32, vertices []float32, indices []uint16, color *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, shader *Shader, uniforms []interface{}, evenOdd bool) {
 	if len(indices) > graphics.IndicesNum {
 		panic(fmt.Sprintf("graphicscommand: len(indices) must be <= graphics.IndicesNum but not at EnqueueDrawTrianglesCommand: len(indices): %d, graphics.IndicesNum: %d", len(indices), graphics.IndicesNum))
 	}
@@ -167,7 +167,7 @@ func (q *commandQueue) EnqueueDrawTrianglesCommand(dst *Image, srcs [graphics.Sh
 	// TODO: If dst is the screen, reorder the command to be the last.
 	if !split && 0 < len(q.commands) {
 		// TODO: Pass offsets and uniforms when merging considers the shader.
-		if last := q.commands[len(q.commands)-1]; last.CanMergeWithDrawTrianglesCommand(dst, srcs, color, mode, filter, address, dstRegion, srcRegion, shader) {
+		if last := q.commands[len(q.commands)-1]; last.CanMergeWithDrawTrianglesCommand(dst, srcs, color, mode, filter, address, dstRegion, srcRegion, shader, evenOdd) {
 			last.AddNumVertices(len(vertices))
 			last.AddNumIndices(len(indices))
 			return
@@ -188,6 +188,7 @@ func (q *commandQueue) EnqueueDrawTrianglesCommand(dst *Image, srcs [graphics.Sh
 		srcRegion: srcRegion,
 		shader:    shader,
 		uniforms:  uniforms,
+		evenOdd:   evenOdd,
 	}
 	q.commands = append(q.commands, c)
 }
@@ -319,6 +320,7 @@ type drawTrianglesCommand struct {
 	srcRegion driver.Region
 	shader    *Shader
 	uniforms  []interface{}
+	evenOdd   bool
 }
 
 func (c *drawTrianglesCommand) String() string {
@@ -428,7 +430,7 @@ func (c *drawTrianglesCommand) Exec(indexOffset int) error {
 		imgs[0] = c.srcs[0].image.ID()
 	}
 
-	return theGraphicsDriver.DrawTriangles(c.dst.image.ID(), imgs, c.offsets, shaderID, c.nindices, indexOffset, c.mode, c.color, c.filter, c.address, c.dstRegion, c.srcRegion, c.uniforms)
+	return theGraphicsDriver.DrawTriangles(c.dst.image.ID(), imgs, c.offsets, shaderID, c.nindices, indexOffset, c.mode, c.color, c.filter, c.address, c.dstRegion, c.srcRegion, c.uniforms, c.evenOdd)
 }
 
 func (c *drawTrianglesCommand) NumVertices() int {
@@ -449,7 +451,7 @@ func (c *drawTrianglesCommand) AddNumIndices(n int) {
 
 // CanMergeWithDrawTrianglesCommand returns a boolean value indicating whether the other drawTrianglesCommand can be merged
 // with the drawTrianglesCommand c.
-func (c *drawTrianglesCommand) CanMergeWithDrawTrianglesCommand(dst *Image, srcs [graphics.ShaderImageNum]*Image, color *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, shader *Shader) bool {
+func (c *drawTrianglesCommand) CanMergeWithDrawTrianglesCommand(dst *Image, srcs [graphics.ShaderImageNum]*Image, color *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, shader *Shader, evenOdd bool) bool {
 	// If a shader is used, commands are not merged.
 	//
 	// TODO: Merge shader commands considering uniform variables.
@@ -480,6 +482,9 @@ func (c *drawTrianglesCommand) CanMergeWithDrawTrianglesCommand(dst *Image, srcs
 	if c.srcRegion != srcRegion {
 		return false
 	}
+	if c.evenOdd != evenOdd {
+		return false
+	}
 	return true
 }
 
@@ -513,7 +518,7 @@ func (c *replacePixelsCommand) AddNumVertices(n int) {
 func (c *replacePixelsCommand) AddNumIndices(n int) {
 }
 
-func (c *replacePixelsCommand) CanMergeWithDrawTrianglesCommand(dst *Image, src [graphics.ShaderImageNum]*Image, color *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, shader *Shader) bool {
+func (c *replacePixelsCommand) CanMergeWithDrawTrianglesCommand(dst *Image, src [graphics.ShaderImageNum]*Image, color *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, shader *Shader, evenOdd bool) bool {
 	return false
 }
 
@@ -550,7 +555,7 @@ func (c *pixelsCommand) AddNumVertices(n int) {
 func (c *pixelsCommand) AddNumIndices(n int) {
 }
 
-func (c *pixelsCommand) CanMergeWithDrawTrianglesCommand(dst *Image, src [graphics.ShaderImageNum]*Image, color *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, shader *Shader) bool {
+func (c *pixelsCommand) CanMergeWithDrawTrianglesCommand(dst *Image, src [graphics.ShaderImageNum]*Image, color *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, shader *Shader, evenOdd bool) bool {
 	return false
 }
 
@@ -583,7 +588,7 @@ func (c *disposeImageCommand) AddNumVertices(n int) {
 func (c *disposeImageCommand) AddNumIndices(n int) {
 }
 
-func (c *disposeImageCommand) CanMergeWithDrawTrianglesCommand(dst *Image, src [graphics.ShaderImageNum]*Image, color *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, shader *Shader) bool {
+func (c *disposeImageCommand) CanMergeWithDrawTrianglesCommand(dst *Image, src [graphics.ShaderImageNum]*Image, color *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, shader *Shader, evenOdd bool) bool {
 	return false
 }
 
@@ -616,7 +621,7 @@ func (c *disposeShaderCommand) AddNumVertices(n int) {
 func (c *disposeShaderCommand) AddNumIndices(n int) {
 }
 
-func (c *disposeShaderCommand) CanMergeWithDrawTrianglesCommand(dst *Image, src [graphics.ShaderImageNum]*Image, color *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, shader *Shader) bool {
+func (c *disposeShaderCommand) CanMergeWithDrawTrianglesCommand(dst *Image, src [graphics.ShaderImageNum]*Image, color *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, shader *Shader, evenOdd bool) bool {
 	return false
 }
 
@@ -655,7 +660,7 @@ func (c *newImageCommand) AddNumVertices(n int) {
 func (c *newImageCommand) AddNumIndices(n int) {
 }
 
-func (c *newImageCommand) CanMergeWithDrawTrianglesCommand(dst *Image, src [graphics.ShaderImageNum]*Image, color *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, shader *Shader) bool {
+func (c *newImageCommand) CanMergeWithDrawTrianglesCommand(dst *Image, src [graphics.ShaderImageNum]*Image, color *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, shader *Shader, evenOdd bool) bool {
 	return false
 }
 
@@ -691,7 +696,7 @@ func (c *newScreenFramebufferImageCommand) AddNumVertices(n int) {
 func (c *newScreenFramebufferImageCommand) AddNumIndices(n int) {
 }
 
-func (c *newScreenFramebufferImageCommand) CanMergeWithDrawTrianglesCommand(dst *Image, src [graphics.ShaderImageNum]*Image, color *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, shader *Shader) bool {
+func (c *newScreenFramebufferImageCommand) CanMergeWithDrawTrianglesCommand(dst *Image, src [graphics.ShaderImageNum]*Image, color *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, shader *Shader, copmlex bool) bool {
 	return false
 }
 
@@ -726,7 +731,7 @@ func (c *newShaderCommand) AddNumVertices(n int) {
 func (c *newShaderCommand) AddNumIndices(n int) {
 }
 
-func (c *newShaderCommand) CanMergeWithDrawTrianglesCommand(dst *Image, src [graphics.ShaderImageNum]*Image, color *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, shader *Shader) bool {
+func (c *newShaderCommand) CanMergeWithDrawTrianglesCommand(dst *Image, src [graphics.ShaderImageNum]*Image, color *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, shader *Shader, evenOdd bool) bool {
 	return false
 }
 

internal/graphicscommand/image.go

@@ -139,7 +139,7 @@ func (i *Image) InternalSize() (int, int) {
 //
 // If the source image is not specified, i.e., src is nil and there is no image in the uniform variables, the
 // elements for the source image are not used.
-func (i *Image) DrawTriangles(srcs [graphics.ShaderImageNum]*Image, offsets [graphics.ShaderImageNum - 1][2]float32, vertices []float32, indices []uint16, clr *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, shader *Shader, uniforms []interface{}) {
+func (i *Image) DrawTriangles(srcs [graphics.ShaderImageNum]*Image, offsets [graphics.ShaderImageNum - 1][2]float32, vertices []float32, indices []uint16, clr *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, shader *Shader, uniforms []interface{}, evenOdd bool) {
 	if shader == nil {
 		// Fast path for rendering without a shader (#1355).
 		img := srcs[0]
@@ -160,7 +160,7 @@ func (i *Image) DrawTriangles(srcs [graphics.ShaderImageNum]*Image, offsets [gra
 	}
 	i.resolveBufferedReplacePixels()
 
-	theCommandQueue.EnqueueDrawTrianglesCommand(i, srcs, offsets, vertices, indices, clr, mode, filter, address, dstRegion, srcRegion, shader, uniforms)
+	theCommandQueue.EnqueueDrawTrianglesCommand(i, srcs, offsets, vertices, indices, clr, mode, filter, address, dstRegion, srcRegion, shader, uniforms, evenOdd)
 }
 
 // Pixels returns the image's pixels.

internal/graphicscommand/image_test.go

@@ -50,7 +50,7 @@ func TestClear(t *testing.T) {
 		Width:  w,
 		Height: h,
 	}
-	dst.DrawTriangles([graphics.ShaderImageNum]*Image{src}, [graphics.ShaderImageNum - 1][2]float32{}, vs, is, nil, driver.CompositeModeClear, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
+	dst.DrawTriangles([graphics.ShaderImageNum]*Image{src}, [graphics.ShaderImageNum - 1][2]float32{}, vs, is, nil, driver.CompositeModeClear, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
 
 	pix, err := dst.Pixels()
 	if err != nil {
@@ -81,8 +81,8 @@ func TestReplacePixelsPartAfterDrawTriangles(t *testing.T) {
 		Width:  w,
 		Height: h,
 	}
-	dst.DrawTriangles([graphics.ShaderImageNum]*Image{clr}, [graphics.ShaderImageNum - 1][2]float32{}, vs, is, nil, driver.CompositeModeClear, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
-	dst.DrawTriangles([graphics.ShaderImageNum]*Image{src}, [graphics.ShaderImageNum - 1][2]float32{}, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
+	dst.DrawTriangles([graphics.ShaderImageNum]*Image{clr}, [graphics.ShaderImageNum - 1][2]float32{}, vs, is, nil, driver.CompositeModeClear, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
+	dst.DrawTriangles([graphics.ShaderImageNum]*Image{src}, [graphics.ShaderImageNum - 1][2]float32{}, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
 	dst.ReplacePixels(make([]byte, 4), 0, 0, 1, 1)
 
 	// TODO: Check the result.
@@ -100,11 +100,11 @@ func TestShader(t *testing.T) {
 		Width:  w,
 		Height: h,
 	}
-	dst.DrawTriangles([graphics.ShaderImageNum]*Image{clr}, [graphics.ShaderImageNum - 1][2]float32{}, vs, is, nil, driver.CompositeModeClear, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
+	dst.DrawTriangles([graphics.ShaderImageNum]*Image{clr}, [graphics.ShaderImageNum - 1][2]float32{}, vs, is, nil, driver.CompositeModeClear, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
 
 	ir := etesting.ShaderProgramFill(0xff, 0, 0, 0xff)
 	s := NewShader(&ir)
-	dst.DrawTriangles([graphics.ShaderImageNum]*Image{}, [graphics.ShaderImageNum - 1][2]float32{}, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, s, nil)
+	dst.DrawTriangles([graphics.ShaderImageNum]*Image{}, [graphics.ShaderImageNum - 1][2]float32{}, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, s, nil, false)
 
 	pix, err := dst.Pixels()
 	if err != nil {

internal/graphicsdriver/metal/graphics.go

@@ -296,11 +296,12 @@ FragmentShaderFunc(0, FILTER_SCREEN, ADDRESS_UNSAFE)
 `
 
 type rpsKey struct {
-	useColorM     bool
-	filter        driver.Filter
-	address       driver.Address
-	compositeMode driver.CompositeMode
-	screen        bool
+	useColorM      bool
+	filter         driver.Filter
+	address        driver.Address
+	compositeMode  driver.CompositeMode
+	colorWriteMask bool
+	screen         bool
 }
 
 type Graphics struct {
@@ -313,7 +314,9 @@ type Graphics struct {
 	rce       mtl.RenderCommandEncoder
 
 	screenDrawable ca.MetalDrawable
+
 	lastDstTexture mtl.Texture
+	lastStencilUse bool
 
 	vb mtl.Buffer
 	ib mtl.Buffer
@@ -334,6 +337,18 @@ type Graphics struct {
 	pool unsafe.Pointer
 }
 
+type stencilMode int
+
+const (
+	prepareStencil stencilMode = iota
+	drawWithStencil
+	noStencil
+)
+
+func (s stencilMode) useStencil() bool {
+	return s != noStencil
+}
+
 var theGraphics Graphics
 
 func Get() *Graphics {
@@ -539,8 +554,9 @@ func (g *Graphics) Reset() error {
 		return err
 	}
 	rpld := mtl.RenderPipelineDescriptor{
-		VertexFunction:   vs,
-		FragmentFunction: fs,
+		VertexFunction:               vs,
+		FragmentFunction:             fs,
+		StencilAttachmentPixelFormat: mtl.PixelFormatStencil8,
 	}
 	rpld.ColorAttachments[0].PixelFormat = g.view.colorPixelFormat()
 	rpld.ColorAttachments[0].BlendingEnabled = true
@@ -548,6 +564,7 @@ func (g *Graphics) Reset() error {
 	rpld.ColorAttachments[0].DestinationRGBBlendFactor = mtl.BlendFactorZero
 	rpld.ColorAttachments[0].SourceAlphaBlendFactor = mtl.BlendFactorOne
 	rpld.ColorAttachments[0].SourceRGBBlendFactor = mtl.BlendFactorOne
+	rpld.ColorAttachments[0].WriteMask = mtl.ColorWriteMaskAll
 	rps, err := g.view.getMTLDevice().MakeRenderPipelineState(rpld)
 	if err != nil {
 		return err
@@ -566,42 +583,51 @@ func (g *Graphics) Reset() error {
 					driver.FilterLinear,
 				} {
 					for c := driver.CompositeModeSourceOver; c <= driver.CompositeModeMax; c++ {
-						cmi := 0
-						if cm {
-							cmi = 1
-						}
-						fs, err := lib.MakeFunction(fmt.Sprintf("FragmentShader_%d_%d_%d", cmi, f, a))
-						if err != nil {
-							return err
-						}
-						rpld := mtl.RenderPipelineDescriptor{
-							VertexFunction:   vs,
-							FragmentFunction: fs,
-						}
+						for _, cwm := range []bool{false, true} {
+							cmi := 0
+							if cm {
+								cmi = 1
+							}
+							fs, err := lib.MakeFunction(fmt.Sprintf("FragmentShader_%d_%d_%d", cmi, f, a))
+							if err != nil {
+								return err
+							}
+							rpld := mtl.RenderPipelineDescriptor{
+								VertexFunction:               vs,
+								FragmentFunction:             fs,
+								StencilAttachmentPixelFormat: mtl.PixelFormatStencil8,
+							}
 
-						pix := mtl.PixelFormatRGBA8UNorm
-						if screen {
-							pix = g.view.colorPixelFormat()
-						}
-						rpld.ColorAttachments[0].PixelFormat = pix
-						rpld.ColorAttachments[0].BlendingEnabled = true
+							pix := mtl.PixelFormatRGBA8UNorm
+							if screen {
+								pix = g.view.colorPixelFormat()
+							}
+							rpld.ColorAttachments[0].PixelFormat = pix
+							rpld.ColorAttachments[0].BlendingEnabled = true
 
-						src, dst := c.Operations()
-						rpld.ColorAttachments[0].DestinationAlphaBlendFactor = operationToBlendFactor(dst)
-						rpld.ColorAttachments[0].DestinationRGBBlendFactor = operationToBlendFactor(dst)
-						rpld.ColorAttachments[0].SourceAlphaBlendFactor = operationToBlendFactor(src)
-						rpld.ColorAttachments[0].SourceRGBBlendFactor = operationToBlendFactor(src)
-						rps, err := g.view.getMTLDevice().MakeRenderPipelineState(rpld)
-						if err != nil {
-							return err
+							src, dst := c.Operations()
+							rpld.ColorAttachments[0].DestinationAlphaBlendFactor = operationToBlendFactor(dst)
+							rpld.ColorAttachments[0].DestinationRGBBlendFactor = operationToBlendFactor(dst)
+							rpld.ColorAttachments[0].SourceAlphaBlendFactor = operationToBlendFactor(src)
+							rpld.ColorAttachments[0].SourceRGBBlendFactor = operationToBlendFactor(src)
+							if cwm {
+								rpld.ColorAttachments[0].WriteMask = mtl.ColorWriteMaskAll
+							} else {
+								rpld.ColorAttachments[0].WriteMask = mtl.ColorWriteMaskNone
+							}
+							rps, err := g.view.getMTLDevice().MakeRenderPipelineState(rpld)
+							if err != nil {
+								return err
+							}
+							g.rpss[rpsKey{
+								screen:         screen,
+								useColorM:      cm,
+								filter:         f,
+								address:        a,
+								compositeMode:  c,
+								colorWriteMask: cwm,
+							}] = rps
 						}
-						g.rpss[rpsKey{
-							screen:        screen,
-							useColorM:     cm,
-							filter:        f,
-							address:       a,
-							compositeMode: c,
-						}] = rps
 					}
 				}
 			}
@@ -619,12 +645,14 @@ func (g *Graphics) flushRenderCommandEncoderIfNeeded() {
 	g.rce.EndEncoding()
 	g.rce = mtl.RenderCommandEncoder{}
 	g.lastDstTexture = mtl.Texture{}
+	g.lastStencilUse = false
 }
 
-func (g *Graphics) draw(rps mtl.RenderPipelineState, dst *Image, dstRegion driver.Region, srcs [graphics.ShaderImageNum]*Image, indexLen int, indexOffset int, uniforms []interface{}) error {
-	if g.lastDstTexture != dst.mtlTexture() {
+func (g *Graphics) draw(rps mtl.RenderPipelineState, dst *Image, dstRegion driver.Region, srcs [graphics.ShaderImageNum]*Image, indexLen int, indexOffset int, uniforms []interface{}, stencilMode stencilMode) error {
+	if g.lastDstTexture != dst.mtlTexture() || g.lastStencilUse != stencilMode.useStencil() {
 		g.flushRenderCommandEncoderIfNeeded()
 	}
+
 	if g.rce == (mtl.RenderCommandEncoder{}) {
 		rpd := mtl.RenderPassDescriptor{}
 		// Even though the destination pixels are not used, mtl.LoadActionDontCare might cause glitches
@@ -640,11 +668,19 @@ func (g *Graphics) draw(rps mtl.RenderPipelineState, dst *Image, dstRegion drive
 		rpd.ColorAttachments[0].Texture = t
 		rpd.ColorAttachments[0].ClearColor = mtl.ClearColor{}
 
+		if stencilMode.useStencil() {
+			dst.ensureStencil()
+			rpd.StencilAttachment.LoadAction = mtl.LoadActionClear
+			rpd.StencilAttachment.StoreAction = mtl.StoreActionDontCare
+			rpd.StencilAttachment.Texture = dst.stencil
+		}
+
 		if g.cb == (mtl.CommandBuffer{}) {
 			g.cb = g.cq.MakeCommandBuffer()
 		}
 		g.rce = g.cb.MakeRenderCommandEncoder(rpd)
 	}
+	g.lastStencilUse = stencilMode.useStencil()
 
 	g.rce.SetRenderPipelineState(rps)
 
@@ -687,11 +723,51 @@ func (g *Graphics) draw(rps mtl.RenderPipelineState, dst *Image, dstRegion drive
 			g.rce.SetFragmentTexture(mtl.Texture{}, i)
 		}
 	}
+
+	// The stencil reference value is always 0 (default).
+	switch stencilMode {
+	case prepareStencil:
+		desc := mtl.DepthStencilDescriptor{
+			BackFaceStencil: mtl.StencilDescriptor{
+				StencilFailureOperation:   mtl.StencilOperationKeep,
+				DepthFailureOperation:     mtl.StencilOperationKeep,
+				DepthStencilPassOperation: mtl.StencilOperationInvert,
+				StencilCompareFunction:    mtl.CompareFunctionAlways,
+			},
+			FrontFaceStencil: mtl.StencilDescriptor{
+				StencilFailureOperation:   mtl.StencilOperationKeep,
+				DepthFailureOperation:     mtl.StencilOperationKeep,
+				DepthStencilPassOperation: mtl.StencilOperationInvert,
+				StencilCompareFunction:    mtl.CompareFunctionAlways,
+			},
+		}
+		g.rce.SetDepthStencilState(g.view.getMTLDevice().MakeDepthStencilState(desc))
+	case drawWithStencil:
+		desc := mtl.DepthStencilDescriptor{
+			BackFaceStencil: mtl.StencilDescriptor{
+				StencilFailureOperation:   mtl.StencilOperationZero,
+				DepthFailureOperation:     mtl.StencilOperationZero,
+				DepthStencilPassOperation: mtl.StencilOperationZero,
+				StencilCompareFunction:    mtl.CompareFunctionNotEqual,
+			},
+			FrontFaceStencil: mtl.StencilDescriptor{
+				StencilFailureOperation:   mtl.StencilOperationZero,
+				DepthFailureOperation:     mtl.StencilOperationZero,
+				DepthStencilPassOperation: mtl.StencilOperationZero,
+				StencilCompareFunction:    mtl.CompareFunctionNotEqual,
+			},
+		}
+		g.rce.SetDepthStencilState(g.view.getMTLDevice().MakeDepthStencilState(desc))
+	case noStencil:
+		g.rce.SetDepthStencilState(mtl.DepthStencilState{})
+	}
+
 	g.rce.DrawIndexedPrimitives(mtl.PrimitiveTypeTriangle, indexLen, mtl.IndexTypeUInt16, g.ib, indexOffset*2)
+
 	return nil
 }
 
-func (g *Graphics) DrawTriangles(dstID driver.ImageID, srcIDs [graphics.ShaderImageNum]driver.ImageID, offsets [graphics.ShaderImageNum - 1][2]float32, shaderID driver.ShaderID, indexLen int, indexOffset int, mode driver.CompositeMode, colorM *affine.ColorM, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, uniforms []interface{}) error {
+func (g *Graphics) DrawTriangles(dstID driver.ImageID, srcIDs [graphics.ShaderImageNum]driver.ImageID, offsets [graphics.ShaderImageNum - 1][2]float32, shaderID driver.ShaderID, indexLen int, indexOffset int, mode driver.CompositeMode, colorM *affine.ColorM, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, uniforms []interface{}, evenOdd bool) error {
 	dst := g.images[dstID]
 
 	if dst.screen {
@@ -703,18 +779,28 @@ func (g *Graphics) DrawTriangles(dstID driver.ImageID, srcIDs [graphics.ShaderIm
 		srcs[i] = g.images[srcID]
 	}
 
-	var rps mtl.RenderPipelineState
+	var rpss [2]mtl.RenderPipelineState
 	var uniformVars []interface{}
 	if shaderID == driver.InvalidShaderID {
 		if dst.screen && filter == driver.FilterScreen {
-			rps = g.screenRPS
+			rpss[1] = g.screenRPS
 		} else {
-			rps = g.rpss[rpsKey{
-				screen:        dst.screen,
-				useColorM:     colorM != nil,
-				filter:        filter,
-				address:       address,
-				compositeMode: mode,
+			useColorM := colorM != nil
+			rpss[0] = g.rpss[rpsKey{
+				screen:         dst.screen,
+				useColorM:      useColorM,
+				filter:         filter,
+				address:        address,
+				compositeMode:  mode,
+				colorWriteMask: false,
+			}]
+			rpss[1] = g.rpss[rpsKey{
+				screen:         dst.screen,
+				useColorM:      useColorM,
+				filter:         filter,
+				address:        address,
+				compositeMode:  mode,
+				colorWriteMask: true,
 			}]
 		}
 
@@ -745,7 +831,11 @@ func (g *Graphics) DrawTriangles(dstID driver.ImageID, srcIDs [graphics.ShaderIm
 		}
 	} else {
 		var err error
-		rps, err = g.shaders[shaderID].RenderPipelineState(g.view.getMTLDevice(), mode)
+		rpss[0], err = g.shaders[shaderID].RenderPipelineState(g.view.getMTLDevice(), mode, false)
+		if err != nil {
+			return err
+		}
+		rpss[1], err = g.shaders[shaderID].RenderPipelineState(g.view.getMTLDevice(), mode, true)
 		if err != nil {
 			return err
 		}
@@ -798,8 +888,17 @@ func (g *Graphics) DrawTriangles(dstID driver.ImageID, srcIDs [graphics.ShaderIm
 		}
 	}
 
-	if err := g.draw(rps, dst, dstRegion, srcs, indexLen, indexOffset, uniformVars); err != nil {
-		return err
+	if evenOdd {
+		if err := g.draw(rpss[0], dst, dstRegion, srcs, indexLen, indexOffset, uniformVars, prepareStencil); err != nil {
+			return err
+		}
+		if err := g.draw(rpss[1], dst, dstRegion, srcs, indexLen, indexOffset, uniformVars, drawWithStencil); err != nil {
+			return err
+		}
+	} else {
+		if err := g.draw(rpss[1], dst, dstRegion, srcs, indexLen, indexOffset, uniformVars, noStencil); err != nil {
+			return err
+		}
 	}
 
 	return nil
@@ -889,6 +988,7 @@ type Image struct {
 	height   int
 	screen   bool
 	texture  mtl.Texture
+	stencil  mtl.Texture
 }
 
 func (i *Image) ID() driver.ImageID {
@@ -903,6 +1003,10 @@ func (i *Image) internalSize() (int, int) {
 }
 
 func (i *Image) Dispose() {
+	if i.stencil != (mtl.Texture{}) {
+		i.stencil.Release()
+		i.stencil = mtl.Texture{}
+	}
 	if i.texture != (mtl.Texture{}) {
 		i.texture.Release()
 		i.texture = mtl.Texture{}
@@ -1022,3 +1126,19 @@ func (i *Image) mtlTexture() mtl.Texture {
 	}
 	return i.texture
 }
+
+func (i *Image) ensureStencil() {
+	if i.stencil != (mtl.Texture{}) {
+		return
+	}
+
+	td := mtl.TextureDescriptor{
+		TextureType: mtl.TextureType2D,
+		PixelFormat: mtl.PixelFormatStencil8,
+		Width:       graphics.InternalImageSize(i.width),
+		Height:      graphics.InternalImageSize(i.height),
+		StorageMode: mtl.StorageModePrivate,
+		Usage:       mtl.TextureUsageRenderTarget,
+	}
+	i.stencil = i.graphics.view.getMTLDevice().MakeTexture(td)
+}

internal/graphicsdriver/metal/shader.go

@@ -26,20 +26,25 @@ import (
 	"github.com/hajimehoshi/ebiten/v2/internal/shaderir/metal"
 )
 
+type shaderRpsKey struct {
+	compositeMode  driver.CompositeMode
+	colorWriteMask bool
+}
+
 type Shader struct {
 	id driver.ShaderID
 
 	ir   *shaderir.Program
 	fs   mtl.Function
 	vs   mtl.Function
-	rpss map[driver.CompositeMode]mtl.RenderPipelineState
+	rpss map[shaderRpsKey]mtl.RenderPipelineState
 }
 
 func newShader(device mtl.Device, id driver.ShaderID, program *shaderir.Program) (*Shader, error) {
 	s := &Shader{
 		id:   id,
 		ir:   program,
-		rpss: map[driver.CompositeMode]mtl.RenderPipelineState{},
+		rpss: map[shaderRpsKey]mtl.RenderPipelineState{},
 	}
 	if err := s.init(device); err != nil {
 		return nil, err
@@ -83,31 +88,43 @@ func (s *Shader) init(device mtl.Device) error {
 	return nil
 }
 
-func (s *Shader) RenderPipelineState(device mtl.Device, c driver.CompositeMode) (mtl.RenderPipelineState, error) {
-	if rps, ok := s.rpss[c]; ok {
+func (s *Shader) RenderPipelineState(device mtl.Device, compositeMode driver.CompositeMode, colorWriteMask bool) (mtl.RenderPipelineState, error) {
+	if rps, ok := s.rpss[shaderRpsKey{
+		compositeMode:  compositeMode,
+		colorWriteMask: colorWriteMask,
+	}]; ok {
 		return rps, nil
 	}
 
 	rpld := mtl.RenderPipelineDescriptor{
-		VertexFunction:   s.vs,
-		FragmentFunction: s.fs,
+		VertexFunction:               s.vs,
+		FragmentFunction:             s.fs,
+		StencilAttachmentPixelFormat: mtl.PixelFormatStencil8,
 	}
 
 	// TODO: For the precise pixel format, whether the render target is the screen or not must be considered.
 	rpld.ColorAttachments[0].PixelFormat = mtl.PixelFormatRGBA8UNorm
 	rpld.ColorAttachments[0].BlendingEnabled = true
 
-	src, dst := c.Operations()
+	src, dst := compositeMode.Operations()
 	rpld.ColorAttachments[0].DestinationAlphaBlendFactor = operationToBlendFactor(dst)
 	rpld.ColorAttachments[0].DestinationRGBBlendFactor = operationToBlendFactor(dst)
 	rpld.ColorAttachments[0].SourceAlphaBlendFactor = operationToBlendFactor(src)
 	rpld.ColorAttachments[0].SourceRGBBlendFactor = operationToBlendFactor(src)
+	if colorWriteMask {
+		rpld.ColorAttachments[0].WriteMask = mtl.ColorWriteMaskAll
+	} else {
+		rpld.ColorAttachments[0].WriteMask = mtl.ColorWriteMaskNone
+	}
 
 	rps, err := device.MakeRenderPipelineState(rpld)
 	if err != nil {
 		return mtl.RenderPipelineState{}, err
 	}
 
-	s.rpss[c] = rps
+	s.rpss[shaderRpsKey{
+		compositeMode:  compositeMode,
+		colorWriteMask: colorWriteMask,
+	}] = rps
 	return rps, nil
 }

internal/graphicsdriver/opengl/context.go

@@ -49,6 +49,7 @@ type context struct {
 	screenFramebuffer  framebufferNative // This might not be the default frame buffer '0' (e.g. iOS).
 	lastFramebuffer    framebufferNative
 	lastTexture        textureNative
+	lastRenderbuffer   renderbufferNative
 	lastViewportWidth  int
 	lastViewportHeight int
 	lastCompositeMode  driver.CompositeMode
@@ -68,6 +69,14 @@ func (c *context) bindTexture(t textureNative) {
 	c.lastTexture = t
 }
 
+func (c *context) bindRenderbuffer(r renderbufferNative) {
+	if c.lastRenderbuffer.equal(r) {
+		return
+	}
+	c.bindRenderbufferImpl(r)
+	c.lastRenderbuffer = r
+}
+
 func (c *context) bindFramebuffer(f framebufferNative) {
 	if c.lastFramebuffer.equal(f) {
 		return

internal/graphicsdriver/opengl/context_desktop.go

@@ -29,17 +29,22 @@ import (
 )
 
 type (
-	textureNative     uint32
-	framebufferNative uint32
-	shader            uint32
-	program           uint32
-	buffer            uint32
+	textureNative      uint32
+	renderbufferNative uint32
+	framebufferNative  uint32
+	shader             uint32
+	program            uint32
+	buffer             uint32
 )
 
 func (t textureNative) equal(rhs textureNative) bool {
 	return t == rhs
 }
 
+func (r renderbufferNative) equal(rhs renderbufferNative) bool {
+	return r == rhs
+}
+
 func (f framebufferNative) equal(rhs framebufferNative) bool {
 	return f == rhs
 }
@@ -198,6 +203,38 @@ func (c *context) isTexture(t textureNative) bool {
 	panic("opengl: isTexture is not implemented")
 }
 
+func (c *context) newRenderbuffer(width, height int) (renderbufferNative, error) {
+	var r uint32
+	gl.GenRenderbuffersEXT(1, &r)
+	if r <= 0 {
+		return 0, errors.New("opengl: creating renderbuffer failed")
+	}
+
+	renderbuffer := renderbufferNative(r)
+	c.bindRenderbuffer(renderbuffer)
+
+	// GL_STENCIL_INDEX8 might not be available with OpenGL 2.1.
+	// https://www.khronos.org/opengl/wiki/Image_Format
+	gl.RenderbufferStorageEXT(gl.RENDERBUFFER, gl.DEPTH24_STENCIL8, int32(width), int32(height))
+
+	return renderbuffer, nil
+}
+
+func (c *context) bindRenderbufferImpl(r renderbufferNative) {
+	gl.BindRenderbufferEXT(gl.RENDERBUFFER, uint32(r))
+}
+
+func (c *context) deleteRenderbuffer(r renderbufferNative) {
+	rr := uint32(r)
+	if !gl.IsRenderbufferEXT(rr) {
+		return
+	}
+	if c.lastRenderbuffer.equal(r) {
+		c.lastRenderbuffer = 0
+	}
+	gl.DeleteRenderbuffersEXT(1, &rr)
+}
+
 func (c *context) newFramebuffer(texture textureNative) (framebufferNative, error) {
 	var f uint32
 	gl.GenFramebuffersEXT(1, &f)
@@ -220,6 +257,17 @@ func (c *context) newFramebuffer(texture textureNative) (framebufferNative, erro
 	return framebufferNative(f), nil
 }
 
+func (c *context) bindStencilBuffer(f framebufferNative, r renderbufferNative) error {
+	c.bindFramebuffer(f)
+
+	gl.FramebufferRenderbufferEXT(gl.FRAMEBUFFER, gl.STENCIL_ATTACHMENT, gl.RENDERBUFFER, uint32(r))
+	if s := gl.CheckFramebufferStatusEXT(gl.FRAMEBUFFER); s != gl.FRAMEBUFFER_COMPLETE {
+		return errors.New(fmt.Sprintf("opengl: glFramebufferRenderbuffer failed: %d", s))
+	}
+	gl.Clear(gl.STENCIL_BUFFER_BIT)
+	return nil
+}
+
 func (c *context) setViewportImpl(width, height int) {
 	gl.Viewport(0, 0, int32(width), int32(height))
 }
@@ -492,3 +540,23 @@ func (c *context) getBufferSubData(buffer buffer, width, height int) []byte {
 	gl.BindBuffer(gl.PIXEL_UNPACK_BUFFER, 0)
 	return pixels
 }
+
+func (c *context) enableStencilTest() {
+	gl.Enable(gl.STENCIL_TEST)
+}
+
+func (c *context) disableStencilTest() {
+	gl.Disable(gl.STENCIL_TEST)
+}
+
+func (c *context) beginStencilWithEvenOddRule() {
+	gl.StencilFunc(gl.ALWAYS, 0x00, 0xff)
+	gl.StencilOp(gl.KEEP, gl.KEEP, gl.INVERT)
+	gl.ColorMask(false, false, false, false)
+}
+
+func (c *context) endStencilWithEvenOddRule() {
+	gl.StencilFunc(gl.NOTEQUAL, 0x00, 0xff)
+	gl.StencilOp(gl.ZERO, gl.ZERO, gl.ZERO)
+	gl.ColorMask(true, true, true, true)
+}

internal/graphicsdriver/opengl/context_js.go

@@ -26,11 +26,12 @@ import (
 )
 
 type (
-	textureNative     js.Value
-	framebufferNative js.Value
-	shader            js.Value
-	buffer            js.Value
-	uniformLocation   js.Value
+	textureNative      js.Value
+	renderbufferNative js.Value
+	framebufferNative  js.Value
+	shader             js.Value
+	buffer             js.Value
+	uniformLocation    js.Value
 
 	attribLocation int
 	programID      int
@@ -44,6 +45,10 @@ func (t textureNative) equal(rhs textureNative) bool {
 	return js.Value(t).Equal(js.Value(rhs))
 }
 
+func (r renderbufferNative) equal(rhs renderbufferNative) bool {
+	return js.Value(r).Equal(js.Value(rhs))
+}
+
 func (f framebufferNative) equal(rhs framebufferNative) bool {
 	return js.Value(f).Equal(js.Value(rhs))
 }
@@ -100,6 +105,7 @@ func (c *context) initGL() {
 		attr := js.Global().Get("Object").New()
 		attr.Set("alpha", true)
 		attr.Set("premultipliedAlpha", true)
+		attr.Set("stencil", true)
 
 		if isWebGL2Available {
 			gl = canvas.Call("getContext", "webgl2", attr)
@@ -165,7 +171,7 @@ func (c *context) newTexture(width, height int) (textureNative, error) {
 	gl := c.gl
 	t := gl.createTexture.Invoke()
 	if !t.Truthy() {
-		return textureNative(js.Null()), errors.New("opengl: glGenTexture failed")
+		return textureNative(js.Null()), errors.New("opengl: createTexture failed")
 	}
 	c.bindTexture(textureNative(t))
 
@@ -240,6 +246,37 @@ func (c *context) isTexture(t textureNative) bool {
 	panic("opengl: isTexture is not implemented")
 }
 
+func (c *context) newRenderbuffer(width, height int) (renderbufferNative, error) {
+	gl := c.gl
+	r := gl.createRenderbuffer.Invoke()
+	if !r.Truthy() {
+		return renderbufferNative(js.Null()), errors.New("opengl: createRenderbuffer failed")
+	}
+
+	c.bindRenderbuffer(renderbufferNative(r))
+	// TODO: Is STENCIL_INDEX8 portable?
+	// https://stackoverflow.com/questions/11084961/binding-a-stencil-render-buffer-to-a-frame-buffer-in-opengl
+	gl.renderbufferStorage.Invoke(gles.RENDERBUFFER, gles.STENCIL_INDEX8, width, height)
+
+	return renderbufferNative(r), nil
+}
+
+func (c *context) bindRenderbufferImpl(r renderbufferNative) {
+	gl := c.gl
+	gl.bindRenderbuffer.Invoke(gles.RENDERBUFFER, js.Value(r))
+}
+
+func (c *context) deleteRenderbuffer(r renderbufferNative) {
+	gl := c.gl
+	if !gl.isRenderbuffer.Invoke(js.Value(r)).Bool() {
+		return
+	}
+	if c.lastRenderbuffer.equal(r) {
+		c.lastRenderbuffer = renderbufferNative(js.Null())
+	}
+	gl.deleteRenderbuffer.Invoke(js.Value(r))
+}
+
 func (c *context) newFramebuffer(t textureNative) (framebufferNative, error) {
 	gl := c.gl
 	f := gl.createFramebuffer.Invoke()
@@ -253,6 +290,18 @@ func (c *context) newFramebuffer(t textureNative) (framebufferNative, error) {
 	return framebufferNative(f), nil
 }
 
+func (c *context) bindStencilBuffer(f framebufferNative, r renderbufferNative) error {
+	gl := c.gl
+	c.bindFramebuffer(f)
+
+	gl.framebufferRenderbuffer.Invoke(gles.FRAMEBUFFER, gles.STENCIL_ATTACHMENT, gles.RENDERBUFFER, js.Value(r))
+	if s := gl.checkFramebufferStatus.Invoke(gles.FRAMEBUFFER); s.Int() != gles.FRAMEBUFFER_COMPLETE {
+		return errors.New(fmt.Sprintf("opengl: framebufferRenderbuffer failed: %d", s.Int()))
+	}
+	gl.clear.Invoke(gles.STENCIL_BUFFER_BIT)
+	return nil
+}
+
 func (c *context) setViewportImpl(width, height int) {
 	gl := c.gl
 	gl.viewport.Invoke(0, 0, width, height)
@@ -598,3 +647,27 @@ func (c *context) getBufferSubData(buffer buffer, width, height int) []byte {
 	gl.bindBuffer.Invoke(gles.PIXEL_UNPACK_BUFFER, nil)
 	return jsutil.Uint8ArrayToSlice(arr, l)
 }
+
+func (c *context) enableStencilTest() {
+	gl := c.gl
+	gl.enable.Invoke(gles.STENCIL_TEST)
+}
+
+func (c *context) disableStencilTest() {
+	gl := c.gl
+	gl.disable.Invoke(gles.STENCIL_TEST)
+}
+
+func (c *context) beginStencilWithEvenOddRule() {
+	gl := c.gl
+	gl.stencilFunc.Invoke(gles.ALWAYS, 0x00, 0xff)
+	gl.stencilOp.Invoke(gles.KEEP, gles.KEEP, gles.INVERT)
+	gl.colorMask.Invoke(false, false, false, false)
+}
+
+func (c *context) endStencilWithEvenOddRule() {
+	gl := c.gl
+	gl.stencilFunc.Invoke(gles.NOTEQUAL, 0x00, 0xff)
+	gl.stencilOp.Invoke(gles.ZERO, gles.ZERO, gles.ZERO)
+	gl.colorMask.Invoke(true, true, true, true)
+}

internal/graphicsdriver/opengl/context_mobile.go

@@ -27,17 +27,22 @@ import (
 )
 
 type (
-	textureNative     uint32
-	framebufferNative uint32
-	shader            uint32
-	program           uint32
-	buffer            uint32
+	textureNative      uint32
+	renderbufferNative uint32
+	framebufferNative  uint32
+	shader             uint32
+	program            uint32
+	buffer             uint32
 )
 
 func (t textureNative) equal(rhs textureNative) bool {
 	return t == rhs
 }
 
+func (r renderbufferNative) equal(rhs renderbufferNative) bool {
+	return r == rhs
+}
+
 func (f framebufferNative) equal(rhs framebufferNative) bool {
 	return f == rhs
 }
@@ -185,6 +190,34 @@ func (c *context) isTexture(t textureNative) bool {
 	return c.ctx.IsTexture(uint32(t))
 }
 
+func (c *context) newRenderbuffer(width, height int) (renderbufferNative, error) {
+	r := c.ctx.GenRenderbuffers(1)[0]
+	if r <= 0 {
+		return 0, errors.New("opengl: creating renderbuffer failed")
+	}
+
+	renderbuffer := renderbufferNative(r)
+	c.bindRenderbuffer(renderbuffer)
+
+	c.ctx.RenderbufferStorage(gles.RENDERBUFFER, gles.STENCIL_INDEX8, int32(width), int32(height))
+
+	return renderbuffer, nil
+}
+
+func (c *context) bindRenderbufferImpl(r renderbufferNative) {
+	c.ctx.BindRenderbuffer(gles.RENDERBUFFER, uint32(r))
+}
+
+func (c *context) deleteRenderbuffer(r renderbufferNative) {
+	if !c.ctx.IsRenderbuffer(uint32(r)) {
+		return
+	}
+	if c.lastRenderbuffer.equal(r) {
+		c.lastRenderbuffer = 0
+	}
+	c.ctx.DeleteRenderbuffers([]uint32{uint32(r)})
+}
+
 func (c *context) newFramebuffer(texture textureNative) (framebufferNative, error) {
 	f := c.ctx.GenFramebuffers(1)[0]
 	if f <= 0 {
@@ -206,6 +239,17 @@ func (c *context) newFramebuffer(texture textureNative) (framebufferNative, erro
 	return framebufferNative(f), nil
 }
 
+func (c *context) bindStencilBuffer(f framebufferNative, r renderbufferNative) error {
+	c.bindFramebuffer(f)
+
+	c.ctx.FramebufferRenderbuffer(gles.FRAMEBUFFER, gles.STENCIL_ATTACHMENT, gles.RENDERBUFFER, uint32(r))
+	if s := c.ctx.CheckFramebufferStatus(gles.FRAMEBUFFER); s != gles.FRAMEBUFFER_COMPLETE {
+		return errors.New(fmt.Sprintf("opengl: glFramebufferRenderbuffer failed: %d", s))
+	}
+	c.ctx.Clear(gles.STENCIL_BUFFER_BIT)
+	return nil
+}
+
 func (c *context) setViewportImpl(width, height int) {
 	c.ctx.Viewport(0, 0, int32(width), int32(height))
 }
@@ -457,3 +501,23 @@ func (c *context) getBufferSubData(buffer buffer, width, height int) []byte {
 	// As PBO is not used in mobiles, leave this unimplemented so far.
 	panic("opengl: getBufferSubData is not implemented for mobiles")
 }
+
+func (c *context) enableStencilTest() {
+	c.ctx.Enable(gles.STENCIL_TEST)
+}
+
+func (c *context) disableStencilTest() {
+	c.ctx.Disable(gles.STENCIL_TEST)
+}
+
+func (c *context) beginStencilWithEvenOddRule() {
+	c.ctx.StencilFunc(gles.ALWAYS, 0x00, 0xff)
+	c.ctx.StencilOp(gles.KEEP, gles.KEEP, gles.INVERT)
+	c.ctx.ColorMask(false, false, false, false)
+}
+
+func (c *context) endStencilWithEvenOddRule() {
+	c.ctx.StencilFunc(gles.NOTEQUAL, 0x00, 0xff)
+	c.ctx.StencilOp(gles.ZERO, gles.ZERO, gles.ZERO)
+	c.ctx.ColorMask(true, true, true, true)
+}

internal/graphicsdriver/opengl/graphics.go

@@ -142,7 +142,7 @@ func (g *Graphics) SetVertices(vertices []float32, indices []uint16) {
 	g.context.elementArrayBufferSubData(indices)
 }
 
-func (g *Graphics) DrawTriangles(dstID driver.ImageID, srcIDs [graphics.ShaderImageNum]driver.ImageID, offsets [graphics.ShaderImageNum - 1][2]float32, shaderID driver.ShaderID, indexLen int, indexOffset int, mode driver.CompositeMode, colorM *affine.ColorM, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, uniforms []interface{}) error {
+func (g *Graphics) DrawTriangles(dstID driver.ImageID, srcIDs [graphics.ShaderImageNum]driver.ImageID, offsets [graphics.ShaderImageNum - 1][2]float32, shaderID driver.ShaderID, indexLen int, indexOffset int, mode driver.CompositeMode, colorM *affine.ColorM, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, uniforms []interface{}, evenOdd bool) error {
 	destination := g.images[dstID]
 
 	if !destination.pbo.equal(*new(buffer)) {
@@ -308,7 +308,20 @@ func (g *Graphics) DrawTriangles(dstID driver.ImageID, srcIDs [graphics.ShaderIm
 		return err
 	}
 
+	if evenOdd {
+		if err := destination.ensureStencilBuffer(); err != nil {
+			return err
+		}
+		g.context.enableStencilTest()
+		g.context.beginStencilWithEvenOddRule()
+		g.context.drawElements(indexLen, indexOffset*2)
+		g.context.endStencilWithEvenOddRule()
+	}
 	g.context.drawElements(indexLen, indexOffset*2) // 2 is uint16 size in bytes
+	if evenOdd {
+		g.context.disableStencilTest()
+	}
+
 	return nil
 }
 

internal/graphicsdriver/opengl/image.go

@@ -23,6 +23,7 @@ type Image struct {
 	id          driver.ImageID
 	graphics    *Graphics
 	texture     textureNative
+	stencil     renderbufferNative
 	framebuffer *framebuffer
 	pbo         buffer
 	width       int
@@ -48,6 +49,9 @@ func (i *Image) Dispose() {
 	if !i.texture.equal(*new(textureNative)) {
 		i.graphics.context.deleteTexture(i.texture)
 	}
+	if !i.stencil.equal(*new(renderbufferNative)) {
+		i.graphics.context.deleteRenderbuffer(i.stencil)
+	}
 
 	i.graphics.removeImage(i)
 }
@@ -105,6 +109,27 @@ func (i *Image) ensureFramebuffer() error {
 	return nil
 }
 
+func (i *Image) ensureStencilBuffer() error {
+	if !i.stencil.equal(*new(renderbufferNative)) {
+		return nil
+	}
+
+	if err := i.ensureFramebuffer(); err != nil {
+		return err
+	}
+
+	r, err := i.graphics.context.newRenderbuffer(i.framebufferSize())
+	if err != nil {
+		return err
+	}
+	i.stencil = r
+
+	if err := i.graphics.context.bindStencilBuffer(i.framebuffer.native, i.stencil); err != nil {
+		return err
+	}
+	return nil
+}
+
 func (i *Image) ReplacePixels(args []*driver.ReplacePixelsArgs) {
 	if i.screen {
 		panic("opengl: ReplacePixels cannot be called on the screen, that doesn't have a texture")

internal/mipmap/mipmap.go

@@ -85,7 +85,7 @@ func (m *Mipmap) Pixels(x, y, width, height int) ([]byte, error) {
 	return m.orig.Pixels(x, y, width, height)
 }
 
-func (m *Mipmap) DrawTriangles(srcs [graphics.ShaderImageNum]*Mipmap, vertices []float32, indices []uint16, colorm *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, subimageOffsets [graphics.ShaderImageNum - 1][2]float32, shader *Shader, uniforms []interface{}, canSkipMipmap bool) {
+func (m *Mipmap) DrawTriangles(srcs [graphics.ShaderImageNum]*Mipmap, vertices []float32, indices []uint16, colorm *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, subimageOffsets [graphics.ShaderImageNum - 1][2]float32, shader *Shader, uniforms []interface{}, evenOdd bool, canSkipMipmap bool) {
 	if len(indices) == 0 {
 		return
 	}
@@ -164,7 +164,7 @@ func (m *Mipmap) DrawTriangles(srcs [graphics.ShaderImageNum]*Mipmap, vertices [
 		imgs[i] = src.orig
 	}
 
-	m.orig.DrawTriangles(imgs, vertices, indices, colorm, mode, filter, address, dstRegion, srcRegion, subimageOffsets, s, uniforms)
+	m.orig.DrawTriangles(imgs, vertices, indices, colorm, mode, filter, address, dstRegion, srcRegion, subimageOffsets, s, uniforms, evenOdd)
 	m.disposeMipmaps()
 }
 
@@ -226,7 +226,7 @@ func (m *Mipmap) level(level int) *buffered.Image {
 		Width:  float32(w2),
 		Height: float32(h2),
 	}
-	s.DrawTriangles([graphics.ShaderImageNum]*buffered.Image{src}, vs, is, nil, driver.CompositeModeCopy, filter, driver.AddressUnsafe, dstRegion, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil)
+	s.DrawTriangles([graphics.ShaderImageNum]*buffered.Image{src}, vs, is, nil, driver.CompositeModeCopy, filter, driver.AddressUnsafe, dstRegion, driver.Region{}, [graphics.ShaderImageNum - 1][2]float32{}, nil, nil, false)
 	m.imgs[level] = s
 
 	return m.imgs[level]

internal/restorable/image.go

@@ -76,6 +76,7 @@ type drawTrianglesHistoryItem struct {
 	srcRegion driver.Region
 	shader    *Shader
 	uniforms  []interface{}
+	evenOdd   bool
 }
 
 // Image represents an image that can be restored when GL context is lost.
@@ -186,7 +187,7 @@ func (i *Image) Extend(width, height int) *Image {
 		Width:  float32(sw),
 		Height: float32(sh),
 	}
-	newImg.DrawTriangles(srcs, offsets, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
+	newImg.DrawTriangles(srcs, offsets, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
 
 	// Overwrite the history as if the image newImg is created only by ReplacePixels. Now drawTrianglesHistory
 	// and basePixels cannot be mixed.
@@ -247,7 +248,7 @@ func clearImage(i *graphicscommand.Image) {
 		Width:  float32(dw),
 		Height: float32(dh),
 	}
-	i.DrawTriangles(srcs, offsets, vs, is, nil, driver.CompositeModeClear, driver.FilterNearest, driver.AddressUnsafe, dstRegion, driver.Region{}, nil, nil)
+	i.DrawTriangles(srcs, offsets, vs, is, nil, driver.CompositeModeClear, driver.FilterNearest, driver.AddressUnsafe, dstRegion, driver.Region{}, nil, nil, false)
 }
 
 // BasePixelsForTesting returns the image's basePixels for testing.
@@ -350,7 +351,7 @@ func (i *Image) ReplacePixels(pixels []byte, x, y, width, height int) {
 //   5: Color G
 //   6: Color B
 //   7: Color Y
-func (i *Image) DrawTriangles(srcs [graphics.ShaderImageNum]*Image, offsets [graphics.ShaderImageNum - 1][2]float32, vertices []float32, indices []uint16, colorm *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, shader *Shader, uniforms []interface{}) {
+func (i *Image) DrawTriangles(srcs [graphics.ShaderImageNum]*Image, offsets [graphics.ShaderImageNum - 1][2]float32, vertices []float32, indices []uint16, colorm *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, shader *Shader, uniforms []interface{}, evenOdd bool) {
 	if i.priority {
 		panic("restorable: DrawTriangles cannot be called on a priority image")
 	}
@@ -374,7 +375,7 @@ func (i *Image) DrawTriangles(srcs [graphics.ShaderImageNum]*Image, offsets [gra
 	if srcstale || i.screen || !NeedsRestoring() || i.volatile {
 		i.makeStale()
 	} else {
-		i.appendDrawTrianglesHistory(srcs, offsets, vertices, indices, colorm, mode, filter, address, dstRegion, srcRegion, shader, uniforms)
+		i.appendDrawTrianglesHistory(srcs, offsets, vertices, indices, colorm, mode, filter, address, dstRegion, srcRegion, shader, uniforms, evenOdd)
 	}
 
 	var s *graphicscommand.Shader
@@ -391,11 +392,11 @@ func (i *Image) DrawTriangles(srcs [graphics.ShaderImageNum]*Image, offsets [gra
 		}
 		s = shader.shader
 	}
-	i.image.DrawTriangles(imgs, offsets, vertices, indices, colorm, mode, filter, address, dstRegion, srcRegion, s, uniforms)
+	i.image.DrawTriangles(imgs, offsets, vertices, indices, colorm, mode, filter, address, dstRegion, srcRegion, s, uniforms, evenOdd)
 }
 
 // appendDrawTrianglesHistory appends a draw-image history item to the image.
-func (i *Image) appendDrawTrianglesHistory(srcs [graphics.ShaderImageNum]*Image, offsets [graphics.ShaderImageNum - 1][2]float32, vertices []float32, indices []uint16, colorm *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, shader *Shader, uniforms []interface{}) {
+func (i *Image) appendDrawTrianglesHistory(srcs [graphics.ShaderImageNum]*Image, offsets [graphics.ShaderImageNum - 1][2]float32, vertices []float32, indices []uint16, colorm *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address, dstRegion, srcRegion driver.Region, shader *Shader, uniforms []interface{}, evenOdd bool) {
 	if i.stale || i.volatile || i.screen {
 		return
 	}
@@ -427,6 +428,7 @@ func (i *Image) appendDrawTrianglesHistory(srcs [graphics.ShaderImageNum]*Image,
 		srcRegion: srcRegion,
 		shader:    shader,
 		uniforms:  uniforms,
+		evenOdd:   evenOdd,
 	}
 	i.drawTrianglesHistory = append(i.drawTrianglesHistory, item)
 }
@@ -605,7 +607,7 @@ func (i *Image) restore() error {
 			}
 			imgs[i] = img.image
 		}
-		gimg.DrawTriangles(imgs, c.offsets, c.vertices, c.indices, c.colorm, c.mode, c.filter, c.address, c.dstRegion, c.srcRegion, s, c.uniforms)
+		gimg.DrawTriangles(imgs, c.offsets, c.vertices, c.indices, c.colorm, c.mode, c.filter, c.address, c.dstRegion, c.srcRegion, s, c.uniforms, c.evenOdd)
 	}
 
 	if len(i.drawTrianglesHistory) > 0 {

internal/restorable/images_test.go

@@ -137,7 +137,7 @@ func TestRestoreChain(t *testing.T) {
 			Width:  1,
 			Height: 1,
 		}
-		imgs[i+1].DrawTriangles([graphics.ShaderImageNum]*Image{imgs[i]}, [graphics.ShaderImageNum - 1][2]float32{}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
+		imgs[i+1].DrawTriangles([graphics.ShaderImageNum]*Image{imgs[i]}, [graphics.ShaderImageNum - 1][2]float32{}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
 	}
 	if err := ResolveStaleImages(); err != nil {
 		t.Fatal(err)
@@ -185,10 +185,10 @@ func TestRestoreChain2(t *testing.T) {
 		Width:  w,
 		Height: h,
 	}
-	imgs[8].DrawTriangles([graphics.ShaderImageNum]*Image{imgs[7]}, [graphics.ShaderImageNum - 1][2]float32{}, quadVertices(w, h, 0, 0), is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
-	imgs[9].DrawTriangles([graphics.ShaderImageNum]*Image{imgs[8]}, [graphics.ShaderImageNum - 1][2]float32{}, quadVertices(w, h, 0, 0), is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
+	imgs[8].DrawTriangles([graphics.ShaderImageNum]*Image{imgs[7]}, [graphics.ShaderImageNum - 1][2]float32{}, quadVertices(w, h, 0, 0), is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
+	imgs[9].DrawTriangles([graphics.ShaderImageNum]*Image{imgs[8]}, [graphics.ShaderImageNum - 1][2]float32{}, quadVertices(w, h, 0, 0), is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
 	for i := 0; i < 7; i++ {
-		imgs[i+1].DrawTriangles([graphics.ShaderImageNum]*Image{imgs[i]}, [graphics.ShaderImageNum - 1][2]float32{}, quadVertices(w, h, 0, 0), is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
+		imgs[i+1].DrawTriangles([graphics.ShaderImageNum]*Image{imgs[i]}, [graphics.ShaderImageNum - 1][2]float32{}, quadVertices(w, h, 0, 0), is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
 	}
 
 	if err := ResolveStaleImages(); err != nil {
@@ -234,10 +234,10 @@ func TestRestoreOverrideSource(t *testing.T) {
 		Width:  w,
 		Height: h,
 	}
-	img2.DrawTriangles([graphics.ShaderImageNum]*Image{img1}, [graphics.ShaderImageNum - 1][2]float32{}, quadVertices(w, h, 0, 0), is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
-	img3.DrawTriangles([graphics.ShaderImageNum]*Image{img2}, [graphics.ShaderImageNum - 1][2]float32{}, quadVertices(w, h, 0, 0), is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
+	img2.DrawTriangles([graphics.ShaderImageNum]*Image{img1}, [graphics.ShaderImageNum - 1][2]float32{}, quadVertices(w, h, 0, 0), is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
+	img3.DrawTriangles([graphics.ShaderImageNum]*Image{img2}, [graphics.ShaderImageNum - 1][2]float32{}, quadVertices(w, h, 0, 0), is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
 	img0.ReplacePixels([]byte{clr1.R, clr1.G, clr1.B, clr1.A}, 0, 0, w, h)
-	img1.DrawTriangles([graphics.ShaderImageNum]*Image{img0}, [graphics.ShaderImageNum - 1][2]float32{}, quadVertices(w, h, 0, 0), is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
+	img1.DrawTriangles([graphics.ShaderImageNum]*Image{img0}, [graphics.ShaderImageNum - 1][2]float32{}, quadVertices(w, h, 0, 0), is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
 	if err := ResolveStaleImages(); err != nil {
 		t.Fatal(err)
 	}
@@ -323,23 +323,23 @@ func TestRestoreComplexGraph(t *testing.T) {
 		Height: h,
 	}
 	var offsets [graphics.ShaderImageNum - 1][2]float32
-	img3.DrawTriangles([graphics.ShaderImageNum]*Image{img0}, offsets, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
+	img3.DrawTriangles([graphics.ShaderImageNum]*Image{img0}, offsets, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
 	vs = quadVertices(w, h, 1, 0)
-	img3.DrawTriangles([graphics.ShaderImageNum]*Image{img1}, offsets, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
+	img3.DrawTriangles([graphics.ShaderImageNum]*Image{img1}, offsets, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
 	vs = quadVertices(w, h, 1, 0)
-	img4.DrawTriangles([graphics.ShaderImageNum]*Image{img1}, offsets, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
+	img4.DrawTriangles([graphics.ShaderImageNum]*Image{img1}, offsets, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
 	vs = quadVertices(w, h, 2, 0)
-	img4.DrawTriangles([graphics.ShaderImageNum]*Image{img2}, offsets, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
+	img4.DrawTriangles([graphics.ShaderImageNum]*Image{img2}, offsets, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
 	vs = quadVertices(w, h, 0, 0)
-	img5.DrawTriangles([graphics.ShaderImageNum]*Image{img3}, offsets, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
+	img5.DrawTriangles([graphics.ShaderImageNum]*Image{img3}, offsets, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
 	vs = quadVertices(w, h, 0, 0)
-	img6.DrawTriangles([graphics.ShaderImageNum]*Image{img3}, offsets, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
+	img6.DrawTriangles([graphics.ShaderImageNum]*Image{img3}, offsets, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
 	vs = quadVertices(w, h, 1, 0)
-	img6.DrawTriangles([graphics.ShaderImageNum]*Image{img4}, offsets, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
+	img6.DrawTriangles([graphics.ShaderImageNum]*Image{img4}, offsets, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
 	vs = quadVertices(w, h, 0, 0)
-	img7.DrawTriangles([graphics.ShaderImageNum]*Image{img2}, offsets, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
+	img7.DrawTriangles([graphics.ShaderImageNum]*Image{img2}, offsets, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
 	vs = quadVertices(w, h, 2, 0)
-	img7.DrawTriangles([graphics.ShaderImageNum]*Image{img3}, offsets, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
+	img7.DrawTriangles([graphics.ShaderImageNum]*Image{img3}, offsets, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
 	if err := ResolveStaleImages(); err != nil {
 		t.Fatal(err)
 	}
@@ -437,8 +437,8 @@ func TestRestoreRecursive(t *testing.T) {
 		Width:  w,
 		Height: h,
 	}
-	img1.DrawTriangles([graphics.ShaderImageNum]*Image{img0}, [graphics.ShaderImageNum - 1][2]float32{}, quadVertices(w, h, 1, 0), is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
-	img0.DrawTriangles([graphics.ShaderImageNum]*Image{img1}, [graphics.ShaderImageNum - 1][2]float32{}, quadVertices(w, h, 1, 0), is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
+	img1.DrawTriangles([graphics.ShaderImageNum]*Image{img0}, [graphics.ShaderImageNum - 1][2]float32{}, quadVertices(w, h, 1, 0), is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
+	img0.DrawTriangles([graphics.ShaderImageNum]*Image{img1}, [graphics.ShaderImageNum - 1][2]float32{}, quadVertices(w, h, 1, 0), is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
 	if err := ResolveStaleImages(); err != nil {
 		t.Fatal(err)
 	}
@@ -538,7 +538,7 @@ func TestDrawTrianglesAndReplacePixels(t *testing.T) {
 		Width:  2,
 		Height: 1,
 	}
-	img1.DrawTriangles([graphics.ShaderImageNum]*Image{img0}, [graphics.ShaderImageNum - 1][2]float32{}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
+	img1.DrawTriangles([graphics.ShaderImageNum]*Image{img0}, [graphics.ShaderImageNum - 1][2]float32{}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
 	img1.ReplacePixels([]byte{0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff}, 0, 0, 2, 1)
 
 	if err := ResolveStaleImages(); err != nil {
@@ -581,8 +581,8 @@ func TestDispose(t *testing.T) {
 		Width:  1,
 		Height: 1,
 	}
-	img1.DrawTriangles([graphics.ShaderImageNum]*Image{img2}, [graphics.ShaderImageNum - 1][2]float32{}, quadVertices(1, 1, 0, 0), is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
-	img0.DrawTriangles([graphics.ShaderImageNum]*Image{img1}, [graphics.ShaderImageNum - 1][2]float32{}, quadVertices(1, 1, 0, 0), is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
+	img1.DrawTriangles([graphics.ShaderImageNum]*Image{img2}, [graphics.ShaderImageNum - 1][2]float32{}, quadVertices(1, 1, 0, 0), is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
+	img0.DrawTriangles([graphics.ShaderImageNum]*Image{img1}, [graphics.ShaderImageNum - 1][2]float32{}, quadVertices(1, 1, 0, 0), is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
 	img1.Dispose()
 
 	if err := ResolveStaleImages(); err != nil {
@@ -696,7 +696,7 @@ func TestReplacePixelsOnly(t *testing.T) {
 		Width:  1,
 		Height: 1,
 	}
-	img1.DrawTriangles([graphics.ShaderImageNum]*Image{img0}, [graphics.ShaderImageNum - 1][2]float32{}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
+	img1.DrawTriangles([graphics.ShaderImageNum]*Image{img0}, [graphics.ShaderImageNum - 1][2]float32{}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
 	img0.ReplacePixels([]byte{5, 6, 7, 8}, 0, 0, 1, 1)
 
 	// BasePixelsForTesting is available without GPU accessing.
@@ -756,7 +756,7 @@ func TestReadPixelsFromVolatileImage(t *testing.T) {
 		Width:  w,
 		Height: h,
 	}
-	dst.DrawTriangles([graphics.ShaderImageNum]*Image{src}, [graphics.ShaderImageNum - 1][2]float32{}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
+	dst.DrawTriangles([graphics.ShaderImageNum]*Image{src}, [graphics.ShaderImageNum - 1][2]float32{}, vs, is, nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
 
 	// Read the pixels. If the implementation is correct, dst tries to read its pixels from GPU due to being
 	// stale.
@@ -783,7 +783,7 @@ func TestAllowReplacePixelsAfterDrawTriangles(t *testing.T) {
 		Width:  w,
 		Height: h,
 	}
-	dst.DrawTriangles([graphics.ShaderImageNum]*Image{src}, [graphics.ShaderImageNum - 1][2]float32{}, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
+	dst.DrawTriangles([graphics.ShaderImageNum]*Image{src}, [graphics.ShaderImageNum - 1][2]float32{}, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
 	dst.ReplacePixels(make([]byte, 4*w*h), 0, 0, w, h)
 	// ReplacePixels for a whole image doesn't panic.
 }
@@ -807,7 +807,7 @@ func TestDisallowReplacePixelsForPartAfterDrawTriangles(t *testing.T) {
 		Width:  w,
 		Height: h,
 	}
-	dst.DrawTriangles([graphics.ShaderImageNum]*Image{src}, [graphics.ShaderImageNum - 1][2]float32{}, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
+	dst.DrawTriangles([graphics.ShaderImageNum]*Image{src}, [graphics.ShaderImageNum - 1][2]float32{}, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
 	dst.ReplacePixels(make([]byte, 4), 0, 0, 1, 1)
 }
 
@@ -884,7 +884,7 @@ func TestMutateSlices(t *testing.T) {
 		Width:  w,
 		Height: h,
 	}
-	dst.DrawTriangles([graphics.ShaderImageNum]*Image{src}, [graphics.ShaderImageNum - 1][2]float32{}, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
+	dst.DrawTriangles([graphics.ShaderImageNum]*Image{src}, [graphics.ShaderImageNum - 1][2]float32{}, vs, is, nil, driver.CompositeModeSourceOver, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
 	for i := range vs {
 		vs[i] = 0
 	}

internal/restorable/shader_test.go

@@ -48,7 +48,7 @@ func clearImage(img *Image, w, h int) {
 		Width:  float32(w),
 		Height: float32(h),
 	}
-	img.DrawTriangles([graphics.ShaderImageNum]*Image{emptyImage}, [graphics.ShaderImageNum - 1][2]float32{}, vs, is, nil, driver.CompositeModeClear, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil)
+	img.DrawTriangles([graphics.ShaderImageNum]*Image{emptyImage}, [graphics.ShaderImageNum - 1][2]float32{}, vs, is, nil, driver.CompositeModeClear, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, nil, nil, false)
 }
 
 func TestShader(t *testing.T) {
@@ -63,7 +63,7 @@ func TestShader(t *testing.T) {
 		Width:  1,
 		Height: 1,
 	}
-	img.DrawTriangles([graphics.ShaderImageNum]*Image{}, [graphics.ShaderImageNum - 1][2]float32{}, quadVertices(1, 1, 0, 0), graphics.QuadIndices(), nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, s, nil)
+	img.DrawTriangles([graphics.ShaderImageNum]*Image{}, [graphics.ShaderImageNum - 1][2]float32{}, quadVertices(1, 1, 0, 0), graphics.QuadIndices(), nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, s, nil, false)
 
 	if err := ResolveStaleImages(); err != nil {
 		t.Fatal(err)
@@ -99,7 +99,7 @@ func TestShaderChain(t *testing.T) {
 			Width:  1,
 			Height: 1,
 		}
-		imgs[i+1].DrawTriangles([graphics.ShaderImageNum]*Image{imgs[i]}, [graphics.ShaderImageNum - 1][2]float32{}, quadVertices(1, 1, 0, 0), graphics.QuadIndices(), nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, s, nil)
+		imgs[i+1].DrawTriangles([graphics.ShaderImageNum]*Image{imgs[i]}, [graphics.ShaderImageNum - 1][2]float32{}, quadVertices(1, 1, 0, 0), graphics.QuadIndices(), nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, s, nil, false)
 	}
 
 	if err := ResolveStaleImages(); err != nil {
@@ -138,7 +138,7 @@ func TestShaderMultipleSources(t *testing.T) {
 		Width:  1,
 		Height: 1,
 	}
-	dst.DrawTriangles(srcs, offsets, quadVertices(1, 1, 0, 0), graphics.QuadIndices(), nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, s, nil)
+	dst.DrawTriangles(srcs, offsets, quadVertices(1, 1, 0, 0), graphics.QuadIndices(), nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, s, nil, false)
 
 	// Clear one of the sources after DrawTriangles. dst should not be affected.
 	clearImage(srcs[0], 1, 1)
@@ -180,7 +180,7 @@ func TestShaderMultipleSourcesOnOneTexture(t *testing.T) {
 		Width:  1,
 		Height: 1,
 	}
-	dst.DrawTriangles(srcs, offsets, quadVertices(1, 1, 0, 0), graphics.QuadIndices(), nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, s, nil)
+	dst.DrawTriangles(srcs, offsets, quadVertices(1, 1, 0, 0), graphics.QuadIndices(), nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, s, nil, false)
 
 	// Clear one of the sources after DrawTriangles. dst should not be affected.
 	clearImage(srcs[0], 3, 1)
@@ -211,7 +211,7 @@ func TestShaderDispose(t *testing.T) {
 		Width:  1,
 		Height: 1,
 	}
-	img.DrawTriangles([graphics.ShaderImageNum]*Image{}, [graphics.ShaderImageNum - 1][2]float32{}, quadVertices(1, 1, 0, 0), graphics.QuadIndices(), nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, s, nil)
+	img.DrawTriangles([graphics.ShaderImageNum]*Image{}, [graphics.ShaderImageNum - 1][2]float32{}, quadVertices(1, 1, 0, 0), graphics.QuadIndices(), nil, driver.CompositeModeCopy, driver.FilterNearest, driver.AddressUnsafe, dr, driver.Region{}, s, nil, false)
 
 	// Dispose the shader. This should invalidates all the images using this shader i.e., all the images become
 	// stale.

vector/internal/triangulate/math.go

@@ -1,26 +0,0 @@
-// Copyright 2019 The Ebiten Authors
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package triangulate
-
-import (
-	"math"
-)
-
-var nan32 = float32(math.NaN())
-
-type Point struct {
-	X float32
-	Y float32
-}

vector/internal/triangulate/triangulate.go

@@ -1,154 +0,0 @@
-// Copyright 2019 The Ebiten Authors
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package triangulate
-
-import (
-	"fmt"
-)
-
-func cross(v0x, v0y, v1x, v1y float32) float32 {
-	return v0x*v1y - v0y*v1x
-}
-
-func triangleCross(pt0, pt1, pt2 Point) float32 {
-	return cross(pt1.X-pt0.X, pt1.Y-pt0.Y, pt2.X-pt1.X, pt2.Y-pt1.Y)
-}
-
-func adjacentIndices(indices []uint16, idx int) (uint16, uint16, uint16) {
-	return indices[(idx+len(indices)-1)%len(indices)], indices[idx], indices[(idx+1)%len(indices)]
-}
-
-func InTriangle(pt, pt0, pt1, pt2 Point) bool {
-	if pt.X <= pt0.X && pt.X <= pt1.X && pt.X <= pt2.X {
-		return false
-	}
-	if pt.X >= pt0.X && pt.X >= pt1.X && pt.X >= pt2.X {
-		return false
-	}
-	if pt.Y <= pt0.Y && pt.Y <= pt1.Y && pt.Y <= pt2.Y {
-		return false
-	}
-	if pt.Y >= pt0.Y && pt.Y >= pt1.Y && pt.Y >= pt2.Y {
-		return false
-	}
-	c0 := cross(pt.X-pt0.X, pt.Y-pt0.Y, pt1.X-pt0.X, pt1.Y-pt0.Y)
-	c1 := cross(pt.X-pt1.X, pt.Y-pt1.Y, pt2.X-pt1.X, pt2.Y-pt1.Y)
-	c2 := cross(pt.X-pt2.X, pt.Y-pt2.Y, pt0.X-pt2.X, pt0.Y-pt2.Y)
-	return (c0 <= 0 && c1 <= 0 && c2 <= 0) || (c0 >= 0 && c1 >= 0 && c2 >= 0)
-}
-
-// Triangulate triangulates the region surrounded by the points pts and returnes the point indices.
-func Triangulate(pts []Point) []uint16 {
-	if len(pts) < 3 {
-		return nil
-	}
-
-	var currentIndices []uint16
-
-	// Split pts into the two point groups if there are the same points.
-	for i := range pts {
-		for j := 0; j < i; j++ {
-			if pts[i] == pts[j] {
-				is0 := Triangulate(pts[j:i])
-				for idx := range is0 {
-					is0[idx] += uint16(j)
-				}
-				is1 := Triangulate(append(pts[i:], pts[:j]...))
-				for idx := range is1 {
-					is1[idx] = uint16((int(is1[idx]) + i) % len(pts))
-				}
-				return append(is0, is1...)
-			}
-		}
-		currentIndices = append(currentIndices, uint16(i))
-	}
-
-	var indices []uint16
-
-	// Triangulation by Ear Clipping.
-	// https://www.geometrictools.com/Documentation/TriangulationByEarClipping.pdf
-	// TODO: Adopt a more efficient algorithm.
-	for len(currentIndices) >= 3 {
-		// Calculate cross-products and remove unneeded vertices.
-		cs := make([]float32, len(currentIndices))
-		idxToRemove := -1
-
-		// Determine the direction of the polygon from the upper-left point.
-		var upperLeft int
-		for i := range currentIndices {
-			i0, i1, i2 := adjacentIndices(currentIndices, i)
-			pt0 := pts[i0]
-			pt1 := pts[i1]
-			pt2 := pts[i2]
-			c := triangleCross(pt0, pt1, pt2)
-			if c == 0 {
-				idxToRemove = i
-				break
-			}
-			cs[i] = c
-
-			if pts[currentIndices[upperLeft]].X > pts[currentIndices[i]].X {
-				upperLeft = i
-			} else if pts[currentIndices[upperLeft]].X == pts[currentIndices[i]].X &&
-				pts[currentIndices[upperLeft]].Y > pts[currentIndices[i]].Y {
-				upperLeft = i
-			}
-		}
-		if idxToRemove != -1 {
-			currentIndices = append(currentIndices[:idxToRemove], currentIndices[idxToRemove+1:]...)
-			continue
-		}
-
-		clockwise := cs[upperLeft] < 0
-
-		idx := -1
-	index:
-		for i := range currentIndices {
-			c := cs[i]
-			if c == 0 {
-				panic("math: cross value must not be 0")
-			}
-			if c < 0 && !clockwise || c > 0 && clockwise {
-				// The angle is more than 180 degrees. This is not an ear.
-				continue
-			}
-
-			i0, i1, i2 := adjacentIndices(currentIndices, i)
-			pt0 := pts[i0]
-			pt1 := pts[i1]
-			pt2 := pts[i2]
-			for _, j := range currentIndices {
-				if j == i0 || j == i1 || j == i2 {
-					continue
-				}
-				if InTriangle(pts[j], pt0, pt1, pt2) {
-					// If the triangle includes another point, the triangle is not an ear.
-					continue index
-				}
-			}
-			// The angle is less than 180 degrees. This is an ear.
-			idx = i
-			break
-		}
-		if idx < 0 {
-			// TODO: This happens when there is self-crossing.
-			panic(fmt.Sprintf("math: there is no ear in the polygon: %v", pts))
-		}
-		i0, i1, i2 := adjacentIndices(currentIndices, idx)
-		indices = append(indices, i0, i1, i2)
-		currentIndices = append(currentIndices[:idx], currentIndices[idx+1:]...)
-	}
-	return indices
-}

vector/internal/triangulate/triangulate_test.go

@@ -1,328 +0,0 @@
-// Copyright 2019 The Ebiten Authors
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package triangulate_test
-
-import (
-	"math"
-	"reflect"
-	"testing"
-
-	. "github.com/hajimehoshi/ebiten/v2/vector/internal/triangulate"
-)
-
-func TestIsInTriangle(t *testing.T) {
-	tests := []struct {
-		Tri []Point
-		Pt  Point
-		Out bool
-	}{
-		{
-			Tri: []Point{
-				{0, 0},
-				{0, 10},
-				{10, 10},
-			},
-			Pt:  Point{1, 9},
-			Out: true,
-		},
-		{
-			Tri: []Point{
-				{0, 0},
-				{0, 10},
-				{10, 10},
-			},
-			Pt:  Point{8, 9},
-			Out: true,
-		},
-		{
-			Tri: []Point{
-				{0, 0},
-				{0, 10},
-				{10, 10},
-			},
-			Pt:  Point{10, 9},
-			Out: false,
-		},
-		{
-			Tri: []Point{
-				{3, 5},
-				{2, 7},
-				{7, 7},
-			},
-			Pt:  Point{3, 6},
-			Out: true,
-		},
-		{
-			Tri: []Point{
-				{3, 5},
-				{2, 7},
-				{7, 7},
-			},
-			Pt:  Point{7, 6},
-			Out: false,
-		},
-	}
-	for _, tc := range tests {
-		got := InTriangle(tc.Pt, tc.Tri[0], tc.Tri[1], tc.Tri[2])
-		want := tc.Out
-		if got != want {
-			t.Errorf("InTriangle(%v, %v, %v, %v): got: %t, want: %t", tc.Pt, tc.Tri[0], tc.Tri[1], tc.Tri[2], got, want)
-		}
-	}
-}
-
-func TestTriangulate(t *testing.T) {
-	tests := []struct {
-		In  []Point
-		Out []uint16
-	}{
-		{
-			In:  []Point{},
-			Out: nil,
-		},
-		{
-			In: []Point{
-				{0, 0},
-			},
-			Out: nil,
-		},
-		{
-			In: []Point{
-				{0, 0},
-				{0, 1},
-			},
-			Out: nil,
-		},
-		{
-			In: []Point{
-				{0, 0},
-				{0, 0},
-				{1, 1},
-			},
-			Out: nil,
-		},
-		{
-			In: []Point{
-				{0, 0},
-				{0.5, 0.5},
-				{1, 1},
-			},
-			Out: nil,
-		},
-		{
-			In: []Point{
-				{0, 0},
-				{0.5, 0.5},
-				{1.5, 1.5},
-				{1, 1},
-			},
-			Out: nil,
-		},
-		{
-			In: []Point{
-				{0, 0},
-				{0, 1},
-				{1, 1},
-			},
-			Out: []uint16{2, 0, 1},
-		},
-		{
-			In: []Point{
-				{0, 0},
-				{1, 1},
-				{0, 1},
-			},
-			Out: []uint16{2, 0, 1},
-		},
-		{
-			In: []Point{
-				{0, 0},
-				{1, 1},
-				{0, 1},
-				{0, 0.5},
-			},
-			Out: []uint16{2, 0, 1},
-		},
-		{
-			In: []Point{
-				{0, 0},
-				{0, 1},
-				{1, 1},
-				{1, 0},
-			},
-			Out: []uint16{3, 0, 1, 3, 1, 2},
-		},
-		{
-			In: []Point{
-				{2, 2},
-				{2, 7},
-				{7, 7},
-				{7, 6},
-				{3, 6},
-				{3, 5},
-			},
-			Out: []uint16{5, 0, 1, 1, 2, 3, 1, 3, 4, 5, 1, 4},
-		},
-		{
-			In: []Point{
-				{2, 2},
-				{2, 7},
-				{7, 7},
-				{7, 6},
-				{3, 6},
-				{3, 5},
-				{7, 5},
-				{7, 4},
-				{3, 4},
-				{3, 3},
-			},
-			Out: []uint16{9, 0, 1, 1, 2, 3, 1, 3, 4, 9, 1, 4, 8, 5, 6, 8, 6, 7},
-		},
-		{
-			In: []Point{
-				{0, 0},
-				{0, 5},
-				{2, 5},
-				{3, 3},
-				{2, 2},
-				{3, 1},
-				{2, 0},
-			},
-			Out: []uint16{6, 0, 1, 6, 1, 2, 6, 2, 3, 4, 5, 6, 6, 3, 4},
-		},
-		{
-			In: []Point{
-				{0, 0},
-				{0, 5},
-				{2, 5},
-				{2, 5},
-				{3, 3},
-				{2, 2},
-				{2, 2},
-				{3, 1},
-				{2, 0},
-			},
-			Out: []uint16{6, 7, 8, 6, 8, 0, 4, 0, 1, 4, 1, 3},
-		},
-		{
-			In: []Point{
-				{0, 0},
-				{0, 1},
-				{1, 1},
-				{1, 0},
-				{2, 0},
-			},
-			Out: []uint16{3, 0, 1, 3, 1, 2},
-		},
-		{
-			In: []Point{
-				{2, 0},
-				{0, 0},
-				{1, 0},
-				{1, 1},
-				{2, 1},
-			},
-			Out: []uint16{4, 0, 2, 4, 2, 3},
-		},
-		{
-			In: []Point{
-				{2, 0},
-				{2, 1},
-				{1, 1},
-				{1, 0},
-				{0, 0},
-			},
-			Out: []uint16{3, 0, 1, 3, 1, 2},
-		},
-		{
-			// Butterfly
-			In: []Point{
-				{0, 2},
-				{1, 1},
-				{2, 2},
-				{2, 0},
-				{1, 1},
-				{0, 0},
-			},
-			Out: []uint16{3, 1, 2, 0, 4, 5},
-		},
-		{
-			In: []Point{
-				{0, 6},
-				{0, 9},
-				{6, 6},
-				{6, 3},
-				{9, 3},
-				{8, 0},
-				{6, 0},
-				{6, 3},
-			},
-			Out: []uint16{6, 3, 4, 6, 4, 5, 2, 7, 0, 2, 0, 1},
-		},
-		{
-			In: []Point{
-				{0, 4},
-				{0, 6},
-				{2, 6},
-				{2, 5},
-				{3, 5},
-				{3, 4},
-				{4, 4},
-				{4, 2},
-				{6, 2},
-				{6, 1},
-				{5, 1},
-				{5, 0},
-				{4, 0},
-				{4, 2},
-				{2, 2},
-				{2, 3},
-				{1, 3},
-				{1, 4},
-			},
-			Out: []uint16{7, 8, 9, 7, 9, 10, 12, 7, 10, 12, 10, 11, 6, 13, 14, 6, 14, 15, 6, 15, 16, 6, 16, 17, 5, 0, 1, 1, 2, 3, 5, 1, 3, 5, 3, 4},
-		},
-	}
-	for _, tc := range tests {
-		got := Triangulate(tc.In)
-		want := tc.Out
-		if !reflect.DeepEqual(got, want) {
-			t.Errorf("Triangulate(%v): got: %v, want: %v", tc.In, got, want)
-		}
-	}
-}
-
-var benchmarkPath []Point
-
-func init() {
-	const (
-		w = 640
-		h = 480
-	)
-	var p []Point
-	for i := 0; i < w; i++ {
-		x := float32(i)
-		y := h/2 + 80*float32(math.Sin(2*math.Pi*float64(i)/40))
-		p = append(p, Point{X: x, Y: y})
-	}
-	p = append(p, Point{w, h}, Point{0, h})
-	benchmarkPath = p
-}
-
-func BenchmarkTriangulate(b *testing.B) {
-	for n := 0; n < b.N; n++ {
-		Triangulate(benchmarkPath)
-	}
-}

vector/path.go

@@ -18,33 +18,26 @@
 package vector
 
 import (
-	"image"
-	"image/color"
 	"math"
 
 	"github.com/hajimehoshi/ebiten/v2"
-	"github.com/hajimehoshi/ebiten/v2/vector/internal/triangulate"
 )
 
-var (
-	emptyImage    = ebiten.NewImage(3, 3)
-	emptySubImage = emptyImage.SubImage(image.Rect(1, 1, 2, 2)).(*ebiten.Image)
-)
-
-func init() {
-	emptyImage.Fill(color.White)
+type point struct {
+	x float32
+	y float32
 }
 
 // Path represents a collection of path segments.
 type Path struct {
-	segs [][]triangulate.Point
-	cur  triangulate.Point
+	segs [][]point
+	cur  point
 }
 
 // MoveTo skips the current position of the path to the given position (x, y) without adding any strokes.
 func (p *Path) MoveTo(x, y float32) {
-	p.cur = triangulate.Point{X: x, Y: y}
-	p.segs = append(p.segs, []triangulate.Point{p.cur})
+	p.cur = point{x: x, y: y}
+	p.segs = append(p.segs, []point{p.cur})
 }
 
 // LineTo adds a line segument to the path, which starts from the current position and ends to the given position (x, y).
@@ -52,10 +45,10 @@ func (p *Path) MoveTo(x, y float32) {
 // LineTo updates the current position to (x, y).
 func (p *Path) LineTo(x, y float32) {
 	if len(p.segs) == 0 {
-		p.segs = append(p.segs, []triangulate.Point{p.cur})
+		p.segs = append(p.segs, []point{p.cur})
 	}
-	p.segs[len(p.segs)-1] = append(p.segs[len(p.segs)-1], triangulate.Point{X: x, Y: y})
-	p.cur = triangulate.Point{X: x, Y: y}
+	p.segs[len(p.segs)-1] = append(p.segs[len(p.segs)-1], point{x: x, y: y})
+	p.cur = point{x: x, y: y}
 }
 
 // nseg returns a number of segments based on the given two points (x0, y0) and (x1, y1).
@@ -78,69 +71,61 @@ func nseg(x0, y0, x1, y1 float32) int {
 
 // QuadTo adds a quadratic Bézier curve to the path.
 func (p *Path) QuadTo(cpx, cpy, x, y float32) {
+	// TODO: Split more appropriate number of segments.
 	c := p.cur
-	num := nseg(c.X, c.Y, x, y)
+	num := nseg(c.x, c.y, x, y)
 	for t := float32(0.0); t <= 1; t += 1.0 / float32(num) {
-		xf := (1-t)*(1-t)*c.X + 2*t*(1-t)*cpx + t*t*x
-		yf := (1-t)*(1-t)*c.Y + 2*t*(1-t)*cpy + t*t*y
+		xf := (1-t)*(1-t)*c.x + 2*t*(1-t)*cpx + t*t*x
+		yf := (1-t)*(1-t)*c.y + 2*t*(1-t)*cpy + t*t*y
 		p.LineTo(xf, yf)
 	}
 }
 
 // CubicTo adds a cubic Bézier curve to the path.
 func (p *Path) CubicTo(cp0x, cp0y, cp1x, cp1y, x, y float32) {
+	// TODO: Split more appropriate number of segments.
 	c := p.cur
-	num := nseg(c.X, c.Y, x, y)
+	num := nseg(c.x, c.y, x, y)
 	for t := float32(0.0); t <= 1; t += 1.0 / float32(num) {
-		xf := (1-t)*(1-t)*(1-t)*c.X + 3*(1-t)*(1-t)*t*cp0x + 3*(1-t)*t*t*cp1x + t*t*t*x
-		yf := (1-t)*(1-t)*(1-t)*c.Y + 3*(1-t)*(1-t)*t*cp0y + 3*(1-t)*t*t*cp1y + t*t*t*y
+		xf := (1-t)*(1-t)*(1-t)*c.x + 3*(1-t)*(1-t)*t*cp0x + 3*(1-t)*t*t*cp1x + t*t*t*x
+		yf := (1-t)*(1-t)*(1-t)*c.y + 3*(1-t)*(1-t)*t*cp0y + 3*(1-t)*t*t*cp1y + t*t*t*y
 		p.LineTo(xf, yf)
 	}
 }
 
-// FillOptions represents options to fill a path.
-type FillOptions struct {
-	// Color is a color to fill with.
-	Color color.Color
-}
-
-// Fill fills the region of the path with the given options op.
-func (p *Path) Fill(dst *ebiten.Image, op *FillOptions) {
-	var vertices []ebiten.Vertex
-	var indices []uint16
-
-	if op.Color == nil {
-		return
-	}
-
-	r, g, b, a := op.Color.RGBA()
-	var rf, gf, bf, af float32
-	if a == 0 {
-		return
-	}
-	rf = float32(r) / float32(a)
-	gf = float32(g) / float32(a)
-	bf = float32(b) / float32(a)
-	af = float32(a) / 0xffff
+// AppendVerticesAndIndices appends vertices and indices for this path and returns them.
+// AppendVerticesAndIndices works in a similar way to the built-in append function.
+// If the arguments are nils, AppendVerticesAndIndices returns new slices.
+//
+// The returned vertice's SrcX and SrcY are 0, and ColorR, ColorG, ColorB, and ColorA are 1.
+//
+// The returned values are intended to be passed to DrawTriangles or DrawTrianglesShader with EvenOdd option
+// in order to render a complex polygon like a concave polygon, a polygon with holes, or a self-intersecting polygon.
+func (p *Path) AppendVerticesAndIndices(vertices []ebiten.Vertex, indices []uint16) ([]ebiten.Vertex, []uint16) {
+	// TODO: Add tests.
 
 	var base uint16
 	for _, seg := range p.segs {
-		for _, pt := range seg {
+		if len(seg) < 3 {
+			continue
+		}
+		for i, pt := range seg {
 			vertices = append(vertices, ebiten.Vertex{
-				DstX:   pt.X,
-				DstY:   pt.Y,
+				DstX:   pt.x,
+				DstY:   pt.y,
 				SrcX:   0,
 				SrcY:   0,
-				ColorR: rf,
-				ColorG: gf,
-				ColorB: bf,
-				ColorA: af,
+				ColorR: 1,
+				ColorG: 1,
+				ColorB: 1,
+				ColorA: 1,
 			})
-		}
-		for _, idx := range triangulate.Triangulate(seg) {
-			indices = append(indices, idx+base)
+			if i < 2 {
+				continue
+			}
+			indices = append(indices, base, base+uint16(i-1), base+uint16(i))
 		}
 		base += uint16(len(seg))
 	}
-	dst.DrawTriangles(vertices, indices, emptySubImage, nil)
+	return vertices, indices
 }