Saving

examples/mrt/main.go

@@ -0,0 +1,130 @@
+// Copyright 2020 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 main
+
+import (
+	_ "image/jpeg"
+	"log"
+
+	"github.com/hajimehoshi/ebiten/v2"
+)
+
+const (
+	dstSize      = 128
+	screenWidth  = dstSize * 2
+	screenHeight = dstSize * 2
+)
+
+var (
+	dsts = [4]*ebiten.Image{
+		ebiten.NewImage(dstSize, dstSize),
+		ebiten.NewImage(dstSize, dstSize),
+		ebiten.NewImage(dstSize, dstSize),
+		ebiten.NewImage(dstSize, dstSize),
+		/*ebiten.NewImageWithOptions(image.Rect(0, 0, dstSize, dstSize), &ebiten.NewImageOptions{
+			Unmanaged: true,
+		}),
+		ebiten.NewImageWithOptions(image.Rect(0, 0, dstSize, dstSize), &ebiten.NewImageOptions{
+			Unmanaged: true,
+		}),
+		ebiten.NewImageWithOptions(image.Rect(0, 0, dstSize, dstSize), &ebiten.NewImageOptions{
+			Unmanaged: true,
+		}),
+		ebiten.NewImageWithOptions(image.Rect(0, 0, dstSize, dstSize), &ebiten.NewImageOptions{
+			Unmanaged: true,
+		}),*/
+	}
+
+	shaderSrc = []byte(
+		`
+//kage:units pixels
+
+package main
+
+func Fragment(dst vec4, src vec2, color vec4) (vec4, vec4, vec4, vec4) {
+	return vec4(1,0,0,1), vec4(0,1,0,1), vec4(0,0,1,1), vec4(1,0,1,1)
+}
+`)
+	s *ebiten.Shader
+)
+
+func init() {
+	var err error
+
+	s, err = ebiten.NewShader(shaderSrc)
+	if err != nil {
+		log.Fatal(err)
+	}
+}
+
+type Game struct {
+	count int
+}
+
+func (g *Game) Update() error {
+	g.count++
+	return nil
+}
+
+func (g *Game) Draw(screen *ebiten.Image) {
+	vertices := []ebiten.Vertex{
+		{
+			DstX: 0,
+			DstY: 0,
+		},
+		{
+			DstX: dstSize,
+			DstY: 0,
+		},
+		{
+			DstX: 0,
+			DstY: dstSize,
+		},
+		{
+			DstX: dstSize,
+			DstY: dstSize,
+		},
+	}
+	indices := []uint16{0, 1, 2, 1, 2, 3}
+	ebiten.DrawTrianglesShaderMRT(dsts, vertices, indices, s, nil)
+	// Dst 0
+	screen.DrawImage(dsts[0], nil)
+	// Dst 1
+	opts := &ebiten.DrawImageOptions{}
+	opts.GeoM.Translate(dstSize, 0)
+	screen.DrawImage(dsts[1], opts)
+	// Dst 2
+	opts.GeoM.Reset()
+	opts.GeoM.Translate(0, dstSize)
+	screen.DrawImage(dsts[2], opts)
+	// Dst 3
+	opts.GeoM.Reset()
+	opts.GeoM.Translate(dstSize, dstSize)
+	screen.DrawImage(dsts[3], opts)
+}
+
+func (g *Game) Layout(outsideWidth, outsideHeight int) (int, int) {
+	return screenWidth, screenHeight
+}
+
+func main() {
+	ebiten.SetWindowSize(screenWidth, screenHeight)
+	ebiten.SetWindowTitle("MRT (Ebitengine Demo)")
+	if err := ebiten.RunGameWithOptions(&Game{}, &ebiten.RunGameOptions{
+		GraphicsLibrary: ebiten.GraphicsLibraryOpenGL,
+	}); err != nil {
+		log.Fatal(err)
+	}
+}

image.go

@@ -247,7 +247,7 @@ func (i *Image) DrawImage(img *Image, options *DrawImageOptions) {
 	graphics.QuadVertices(vs, float32(sx0), float32(sy0), float32(sx1), float32(sy1), a, b, c, d, tx, ty, cr, cg, cb, ca)
 	is := graphics.QuadIndices()
 
-	srcs := [graphics.ShaderImageCount]*ui.Image{img.image}
+	srcs := [graphics.ShaderSrcImageCount]*ui.Image{img.image}
 
 	useColorM := !colorm.IsIdentity()
 	shader := builtinShader(filter, builtinshader.AddressUnsafe, useColorM)
@@ -262,7 +262,7 @@ func (i *Image) DrawImage(img *Image, options *DrawImageOptions) {
 		})
 	}
 
-	i.image.DrawTriangles(srcs, vs, is, blend, i.adjustedBounds(), [graphics.ShaderImageCount]image.Rectangle{img.adjustedBounds()}, shader.shader, i.tmpUniforms, graphicsdriver.FillAll, canSkipMipmap(geoM, filter), false)
+	i.image.DrawTriangles(srcs, vs, is, blend, i.adjustedBounds(), [graphics.ShaderSrcImageCount]image.Rectangle{img.adjustedBounds()}, shader.shader, i.tmpUniforms, graphicsdriver.FillAll, canSkipMipmap(geoM, filter), false)
 }
 
 // Vertex represents a vertex passed to DrawTriangles.
@@ -500,7 +500,7 @@ func (i *Image) DrawTriangles(vertices []Vertex, indices []uint16, img *Image, o
 		is[i] = uint32(indices[i])
 	}
 
-	srcs := [graphics.ShaderImageCount]*ui.Image{img.image}
+	srcs := [graphics.ShaderSrcImageCount]*ui.Image{img.image}
 
 	useColorM := !colorm.IsIdentity()
 	shader := builtinShader(filter, address, useColorM)
@@ -515,7 +515,7 @@ func (i *Image) DrawTriangles(vertices []Vertex, indices []uint16, img *Image, o
 		})
 	}
 
-	i.image.DrawTriangles(srcs, vs, is, blend, i.adjustedBounds(), [graphics.ShaderImageCount]image.Rectangle{img.adjustedBounds()}, shader.shader, i.tmpUniforms, graphicsdriver.FillRule(options.FillRule), filter != builtinshader.FilterLinear, options.AntiAlias)
+	i.image.DrawTriangles(srcs, vs, is, blend, i.adjustedBounds(), [graphics.ShaderSrcImageCount]image.Rectangle{img.adjustedBounds()}, shader.shader, i.tmpUniforms, graphicsdriver.FillRule(options.FillRule), filter != builtinshader.FilterLinear, options.AntiAlias)
 }
 
 // DrawTrianglesShaderOptions represents options for DrawTrianglesShader.
@@ -565,7 +565,7 @@ type DrawTrianglesShaderOptions struct {
 }
 
 // Check the number of images.
-var _ [len(DrawTrianglesShaderOptions{}.Images) - graphics.ShaderImageCount]struct{} = [0]struct{}{}
+var _ [len(DrawTrianglesShaderOptions{}.Images) - graphics.ShaderSrcImageCount]struct{} = [0]struct{}{}
 
 // DrawTrianglesShader draws triangles with the specified vertices and their indices with the specified shader.
 //
@@ -650,7 +650,7 @@ func (i *Image) DrawTrianglesShader(vertices []Vertex, indices []uint16, shader
 		is[i] = uint32(indices[i])
 	}
 
-	var imgs [graphics.ShaderImageCount]*ui.Image
+	var imgs [graphics.ShaderSrcImageCount]*ui.Image
 	var imgSize image.Point
 	for i, img := range options.Images {
 		if img == nil {
@@ -672,7 +672,7 @@ func (i *Image) DrawTrianglesShader(vertices []Vertex, indices []uint16, shader
 		imgs[i] = img.image
 	}
 
-	var srcRegions [graphics.ShaderImageCount]image.Rectangle
+	var srcRegions [graphics.ShaderSrcImageCount]image.Rectangle
 	for i, img := range options.Images {
 		if img == nil {
 			continue
@@ -686,6 +686,135 @@ func (i *Image) DrawTrianglesShader(vertices []Vertex, indices []uint16, shader
 	i.image.DrawTriangles(imgs, vs, is, blend, i.adjustedBounds(), srcRegions, shader.shader, i.tmpUniforms, graphicsdriver.FillRule(options.FillRule), true, options.AntiAlias)
 }
 
+// DrawTrianglesShader draws triangles with the specified vertices and their indices with the specified shader.
+//
+// Vertex contains color values, which can be interpreted for any purpose by the shader.
+//
+// For the details about the shader, see https://ebitengine.org/en/documents/shader.html.
+//
+// If the shader unit is texels, one of the specified image is non-nil and its size is different from (width, height),
+// DrawTrianglesShader panics.
+// If one of the specified image is non-nil and is disposed, DrawTrianglesShader panics.
+//
+// If len(vertices) is more than MaxVertexCount, the exceeding part is ignored.
+//
+// If len(indices) is not multiple of 3, DrawTrianglesShader panics.
+//
+// If a value in indices is out of range of vertices, or not less than MaxVertexCount, DrawTrianglesShader panics.
+//
+// When a specified image is non-nil and is disposed, DrawTrianglesShader panics.
+//
+// If a specified uniform variable's length or type doesn't match with an expected one, DrawTrianglesShader panics.
+//
+// Even if a result is an invalid color as a premultiplied-alpha color, i.e. an alpha value exceeds other color values,
+// the value is kept and is not clamped.
+//
+// When the image i is disposed, DrawTrianglesShader does nothing.
+func DrawTrianglesShaderMRT(dsts [graphics.ShaderDstImageCount]*Image, vertices []Vertex, indices []uint16, shader *Shader, options *DrawTrianglesShaderOptions) {
+	if dsts[0] == nil || dsts[0].isDisposed() {
+		panic("ebiten: the first destination image given to DrawTrianglesShaderMRT must not be nil or disposed")
+	}
+	var dstImgs [graphics.ShaderDstImageCount]*ui.Image
+	for i, dst := range dsts {
+		if dst == nil {
+			continue
+		}
+		dst.copyCheck()
+		if dst.isDisposed() {
+			panic("ebiten: the destination images given to DrawTrianglesShaderMRT must not be disposed")
+		}
+		dstImgs[i] = dst.image
+	}
+
+	if shader.isDisposed() {
+		panic("ebiten: the given shader to DrawTrianglesShaderMRT must not be disposed")
+	}
+
+	if len(vertices) > graphicscommand.MaxVertexCount {
+		// The last part cannot be specified by indices. Just omit them.
+		vertices = vertices[:graphicscommand.MaxVertexCount]
+	}
+	if len(indices)%3 != 0 {
+		panic("ebiten: len(indices) % 3 must be 0")
+	}
+	for i, idx := range indices {
+		if int(idx) >= len(vertices) {
+			panic(fmt.Sprintf("ebiten: indices[%d] must be less than len(vertices) (%d) but was %d", i, len(vertices), idx))
+		}
+	}
+
+	if options == nil {
+		options = &DrawTrianglesShaderOptions{}
+	}
+
+	var blend graphicsdriver.Blend
+	if options.CompositeMode == CompositeModeCustom {
+		blend = options.Blend.internalBlend()
+	} else {
+		blend = options.CompositeMode.blend().internalBlend()
+	}
+
+	dst := dsts[0]
+	vs := dst.ensureTmpVertices(len(vertices) * graphics.VertexFloatCount)
+	src := options.Images[0]
+	for i, v := range vertices {
+		dx, dy := dst.adjustPositionF32(v.DstX, v.DstY)
+		vs[i*graphics.VertexFloatCount] = dx
+		vs[i*graphics.VertexFloatCount+1] = dy
+		sx, sy := v.SrcX, v.SrcY
+		if src != nil {
+			sx, sy = src.adjustPositionF32(sx, sy)
+		}
+		vs[i*graphics.VertexFloatCount+2] = sx
+		vs[i*graphics.VertexFloatCount+3] = sy
+		vs[i*graphics.VertexFloatCount+4] = v.ColorR
+		vs[i*graphics.VertexFloatCount+5] = v.ColorG
+		vs[i*graphics.VertexFloatCount+6] = v.ColorB
+		vs[i*graphics.VertexFloatCount+7] = v.ColorA
+	}
+
+	is := make([]uint32, len(indices))
+	for i := range is {
+		is[i] = uint32(indices[i])
+	}
+
+	var srcImgs [graphics.ShaderSrcImageCount]*ui.Image
+	var imgSize image.Point
+	for i, img := range options.Images {
+		if img == nil {
+			continue
+		}
+		if img.isDisposed() {
+			panic("ebiten: the given image to DrawTrianglesShader must not be disposed")
+		}
+		if shader.unit == shaderir.Texels {
+			if i == 0 {
+				imgSize = img.Bounds().Size()
+			} else {
+				// TODO: Check imgw > 0 && imgh > 0
+				if img.Bounds().Size() != imgSize {
+					panic("ebiten: all the source images must be the same size with the rectangle")
+				}
+			}
+		}
+		srcImgs[i] = img.image
+	}
+
+	var srcRegions [graphics.ShaderSrcImageCount]image.Rectangle
+	for i, img := range options.Images {
+		if img == nil {
+			continue
+		}
+		srcRegions[i] = img.adjustedBounds()
+	}
+
+	for _, dst := range dsts {
+		dst.tmpUniforms = dst.tmpUniforms[:0]
+		dst.tmpUniforms = shader.appendUniforms(dst.tmpUniforms, options.Uniforms)
+	}
+	ui.DrawTrianglesMRT(dstImgs, srcImgs, vs, is, blend, dst.adjustedBounds(), srcRegions, shader.shader, dst.tmpUniforms, graphicsdriver.FillRule(options.FillRule), true, options.AntiAlias)
+}
+
 // DrawRectShaderOptions represents options for DrawRectShader.
 type DrawRectShaderOptions struct {
 	// GeoM is a geometry matrix to draw.
@@ -724,7 +853,7 @@ type DrawRectShaderOptions struct {
 }
 
 // Check the number of images.
-var _ [len(DrawRectShaderOptions{}.Images)]struct{} = [graphics.ShaderImageCount]struct{}{}
+var _ [len(DrawRectShaderOptions{}.Images)]struct{} = [graphics.ShaderSrcImageCount]struct{}{}
 
 // DrawRectShader draws a rectangle with the specified width and height with the specified shader.
 //
@@ -771,7 +900,7 @@ func (i *Image) DrawRectShader(width, height int, shader *Shader, options *DrawR
 		blend = options.CompositeMode.blend().internalBlend()
 	}
 
-	var imgs [graphics.ShaderImageCount]*ui.Image
+	var imgs [graphics.ShaderSrcImageCount]*ui.Image
 	for i, img := range options.Images {
 		if img == nil {
 			continue
@@ -785,7 +914,7 @@ func (i *Image) DrawRectShader(width, height int, shader *Shader, options *DrawR
 		imgs[i] = img.image
 	}
 
-	var srcRegions [graphics.ShaderImageCount]image.Rectangle
+	var srcRegions [graphics.ShaderSrcImageCount]image.Rectangle
 	for i, img := range options.Images {
 		if img == nil {
 			if shader.unit == shaderir.Pixels && i == 0 {

internal/atlas/image.go

@@ -153,12 +153,12 @@ func (b *backend) extendIfNeeded(width, height int) {
 
 	// Use DrawTriangles instead of WritePixels because the image i might be stale and not have its pixels
 	// information.
-	srcs := [graphics.ShaderImageCount]*graphicscommand.Image{b.image}
+	srcs := [graphics.ShaderSrcImageCount]*graphicscommand.Image{b.image}
 	sw, sh := b.image.InternalSize()
 	vs := quadVertices(0, 0, float32(sw), float32(sh), 0, 0, float32(sw), float32(sh), 1, 1, 1, 1)
 	is := graphics.QuadIndices()
 	dr := image.Rect(0, 0, sw, sh)
-	newImg.DrawTriangles(srcs, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, NearestFilterShader.ensureShader(), nil, graphicsdriver.FillAll)
+	newImg.DrawTriangles(srcs, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, NearestFilterShader.ensureShader(), nil, graphicsdriver.FillAll)
 	b.image.Dispose()
 
 	b.image = newImg
@@ -182,7 +182,7 @@ func newClearedImage(width, height int, screen bool) *graphicscommand.Image {
 func clearImage(i *graphicscommand.Image, region image.Rectangle) {
 	vs := quadVertices(float32(region.Min.X), float32(region.Min.Y), float32(region.Max.X), float32(region.Max.Y), 0, 0, 0, 0, 0, 0, 0, 0)
 	is := graphics.QuadIndices()
-	i.DrawTriangles([graphics.ShaderImageCount]*graphicscommand.Image{}, vs, is, graphicsdriver.BlendClear, region, [graphics.ShaderImageCount]image.Rectangle{}, clearShader.ensureShader(), nil, graphicsdriver.FillAll)
+	i.DrawTriangles([graphics.ShaderSrcImageCount]*graphicscommand.Image{}, vs, is, graphicsdriver.BlendClear, region, [graphics.ShaderSrcImageCount]image.Rectangle{}, clearShader.ensureShader(), nil, graphicsdriver.FillAll)
 }
 
 func (b *backend) clearPixels(region image.Rectangle) {
@@ -355,7 +355,7 @@ func (i *Image) ensureIsolatedFromSource(backends []*backend) {
 	is := graphics.QuadIndices()
 	dr := image.Rect(0, 0, i.width, i.height)
 
-	newI.drawTriangles([graphics.ShaderImageCount]*Image{i}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, NearestFilterShader, nil, graphicsdriver.FillAll)
+	newI.drawTriangles([graphics.ShaderSrcImageCount]*Image{i}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, NearestFilterShader, nil, graphicsdriver.FillAll)
 	newI.moveTo(i)
 }
 
@@ -385,7 +385,7 @@ func (i *Image) putOnSourceBackend(graphicsDriver graphicsdriver.Graphics) {
 	graphics.QuadVertices(vs, 0, 0, w, h, 1, 0, 0, 1, 0, 0, 1, 1, 1, 1)
 	is := graphics.QuadIndices()
 	dr := image.Rect(0, 0, i.width, i.height)
-	newI.drawTriangles([graphics.ShaderImageCount]*Image{i}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, NearestFilterShader, nil, graphicsdriver.FillAll)
+	newI.drawTriangles([graphics.ShaderSrcImageCount]*Image{i}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, NearestFilterShader, nil, graphicsdriver.FillAll)
 
 	newI.moveTo(i)
 	i.usedAsSourceCount = 0
@@ -417,7 +417,7 @@ func (i *Image) regionWithPadding() image.Rectangle {
 //	5: Color G
 //	6: Color B
 //	7: Color Y
-func (i *Image) DrawTriangles(srcs [graphics.ShaderImageCount]*Image, vertices []float32, indices []uint32, blend graphicsdriver.Blend, dstRegion image.Rectangle, srcRegions [graphics.ShaderImageCount]image.Rectangle, shader *Shader, uniforms []uint32, fillRule graphicsdriver.FillRule) {
+func (i *Image) DrawTriangles(srcs [graphics.ShaderSrcImageCount]*Image, vertices []float32, indices []uint32, blend graphicsdriver.Blend, dstRegion image.Rectangle, srcRegions [graphics.ShaderSrcImageCount]image.Rectangle, shader *Shader, uniforms []uint32, fillRule graphicsdriver.FillRule) {
 	backendsM.Lock()
 	defer backendsM.Unlock()
 
@@ -438,7 +438,28 @@ func (i *Image) DrawTriangles(srcs [graphics.ShaderImageCount]*Image, vertices [
 	i.drawTriangles(srcs, vertices, indices, blend, dstRegion, srcRegions, shader, uniforms, fillRule)
 }
 
-func (i *Image) drawTriangles(srcs [graphics.ShaderImageCount]*Image, vertices []float32, indices []uint32, blend graphicsdriver.Blend, dstRegion image.Rectangle, srcRegions [graphics.ShaderImageCount]image.Rectangle, shader *Shader, uniforms []uint32, fillRule graphicsdriver.FillRule) {
+func DrawTrianglesMRT(dsts [graphics.ShaderDstImageCount]*Image, srcs [graphics.ShaderSrcImageCount]*Image, vertices []float32, indices []uint32, blend graphicsdriver.Blend, dstRegion image.Rectangle, srcRegions [graphics.ShaderSrcImageCount]image.Rectangle, shader *Shader, uniforms []uint32, fillRule graphicsdriver.FillRule) {
+	backendsM.Lock()
+	defer backendsM.Unlock()
+
+	if !inFrame {
+		vs := make([]float32, len(vertices))
+		copy(vs, vertices)
+		is := make([]uint32, len(indices))
+		copy(is, indices)
+		us := make([]uint32, len(uniforms))
+		copy(us, uniforms)
+
+		appendDeferred(func() {
+			drawTrianglesMRT(dsts, srcs, vs, is, blend, dstRegion, srcRegions, shader, us, fillRule)
+		})
+		return
+	}
+
+	drawTrianglesMRT(dsts, srcs, vertices, indices, blend, dstRegion, srcRegions, shader, uniforms, fillRule)
+}
+
+func (i *Image) drawTriangles(srcs [graphics.ShaderSrcImageCount]*Image, vertices []float32, indices []uint32, blend graphicsdriver.Blend, dstRegion image.Rectangle, srcRegions [graphics.ShaderSrcImageCount]image.Rectangle, shader *Shader, uniforms []uint32, fillRule graphicsdriver.FillRule) {
 	if len(vertices) == 0 {
 		return
 	}
@@ -515,7 +536,7 @@ func (i *Image) drawTriangles(srcs [graphics.ShaderImageCount]*Image, vertices [
 		srcRegions[i] = srcRegions[i].Add(r.Min)
 	}
 
-	var imgs [graphics.ShaderImageCount]*graphicscommand.Image
+	var imgs [graphics.ShaderSrcImageCount]*graphicscommand.Image
 	for i, src := range srcs {
 		if src == nil {
 			continue
@@ -536,6 +557,113 @@ func (i *Image) drawTriangles(srcs [graphics.ShaderImageCount]*Image, vertices [
 	}
 }
 
+func drawTrianglesMRT(dsts [graphics.ShaderDstImageCount]*Image, srcs [graphics.ShaderSrcImageCount]*Image, vertices []float32, indices []uint32, blend graphicsdriver.Blend, dstRegion image.Rectangle, srcRegions [graphics.ShaderSrcImageCount]image.Rectangle, shader *Shader, uniforms []uint32, fillRule graphicsdriver.FillRule) {
+	if len(vertices) == 0 {
+		return
+	}
+
+	backends := make([]*backend, 0, len(srcs))
+	for _, src := range srcs {
+		if src == nil {
+			continue
+		}
+		if src.backend == nil {
+			// It is possible to spcify i.backend as a forbidden backend, but this might prevent a good allocation for a source image.
+			// If the backend becomes the same as i's, i's backend will be changed at ensureIsolatedFromSource.
+			src.allocate(nil, true)
+		}
+		backends = append(backends, src.backend)
+		src.backend.sourceInThisFrame = true
+	}
+
+	var dstImgs [graphics.ShaderDstImageCount]*graphicscommand.Image
+	for i, dst := range dsts {
+		if dst == nil {
+			continue
+		}
+		dst.ensureIsolatedFromSource(backends)
+		dstImgs[i] = dst.backend.image
+	}
+
+	for _, src := range srcs {
+		// Compare i and source images after ensuring i is not on an atlas, or
+		// i and a source image might share the same atlas even though i != src.
+		for _, dst := range dsts {
+			if src != nil && dst != nil && dst.backend.image == src.backend.image {
+				panic("atlas: Image.DrawTriangles: source must be different from the receiver")
+			}
+		}
+	}
+
+	r := dsts[0].regionWithPadding()
+	// TODO: Check if dstRegion does not to violate the region.
+	dstRegion = dstRegion.Add(r.Min)
+
+	dx, dy := float32(r.Min.X), float32(r.Min.Y)
+
+	var oxf, oyf float32
+	if srcs[0] != nil {
+		r := srcs[0].regionWithPadding()
+		oxf, oyf = float32(r.Min.X), float32(r.Min.Y)
+		n := len(vertices)
+		for i := 0; i < n; i += graphics.VertexFloatCount {
+			vertices[i] += dx
+			vertices[i+1] += dy
+			vertices[i+2] += oxf
+			vertices[i+3] += oyf
+		}
+		if shader.ir.Unit == shaderir.Texels {
+			sw, sh := srcs[0].backend.image.InternalSize()
+			swf, shf := float32(sw), float32(sh)
+			for i := 0; i < n; i += graphics.VertexFloatCount {
+				vertices[i+2] /= swf
+				vertices[i+3] /= shf
+			}
+		}
+	} else {
+		n := len(vertices)
+		for i := 0; i < n; i += graphics.VertexFloatCount {
+			vertices[i] += dx
+			vertices[i+1] += dy
+		}
+	}
+
+	for i, src := range srcs {
+		if src == nil {
+			continue
+		}
+
+		// A source region can be deliberately empty when this is not needed in order to avoid unexpected
+		// performance issue (#1293).
+		if srcRegions[i].Empty() {
+			continue
+		}
+
+		r := src.regionWithPadding()
+		srcRegions[i] = srcRegions[i].Add(r.Min)
+	}
+
+	var srcImgs [graphics.ShaderSrcImageCount]*graphicscommand.Image
+	for i, src := range srcs {
+		if src == nil {
+			continue
+		}
+		srcImgs[i] = src.backend.image
+	}
+
+	graphicscommand.DrawTrianglesMRT(dstImgs, srcImgs, vertices, indices, blend, dstRegion, srcRegions, shader.ensureShader(), uniforms, fillRule)
+
+	for _, src := range srcs {
+		if src == nil {
+			continue
+		}
+		if !src.isOnSourceBackend() && src.canBePutOnAtlas() {
+			// src might already registered, but assigning it again is not harmful.
+			imagesToPutOnSourceBackend.add(src)
+		}
+	}
+}
+
 // WritePixels replaces the pixels on the image.
 func (i *Image) WritePixels(pix []byte, region image.Rectangle) {
 	backendsM.Lock()

internal/atlas/image_test.go

@@ -105,7 +105,7 @@ func TestEnsureIsolatedFromSourceBackend(t *testing.T) {
 	vs := quadVertices(size/2, size/2, size/4, size/4, 1)
 	is := graphics.QuadIndices()
 	dr := image.Rect(0, 0, size, size)
-	img4.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{img3}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
+	img4.DrawTriangles([graphics.ShaderSrcImageCount]*atlas.Image{img3}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
 	if got, want := img4.IsOnSourceBackendForTesting(), false; got != want {
 		t.Errorf("got: %v, want: %v", got, want)
 	}
@@ -113,7 +113,7 @@ func TestEnsureIsolatedFromSourceBackend(t *testing.T) {
 	// img5 is not allocated now, but is allocated at DrawTriangles.
 	vs = quadVertices(0, 0, size/2, size/2, 1)
 	dr = image.Rect(0, 0, size/2, size/2)
-	img3.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{img5}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
+	img3.DrawTriangles([graphics.ShaderSrcImageCount]*atlas.Image{img5}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
 	if got, want := img3.IsOnSourceBackendForTesting(), false; got != want {
 		t.Errorf("got: %v, want: %v", got, want)
 	}
@@ -147,7 +147,7 @@ func TestEnsureIsolatedFromSourceBackend(t *testing.T) {
 	// Check further drawing doesn't cause panic.
 	// This bug was fixed by 03dcd948.
 	vs = quadVertices(0, 0, size/2, size/2, 1)
-	img4.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{img3}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
+	img4.DrawTriangles([graphics.ShaderSrcImageCount]*atlas.Image{img3}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
 }
 
 func TestReputOnSourceBackend(t *testing.T) {
@@ -191,7 +191,7 @@ func TestReputOnSourceBackend(t *testing.T) {
 	// Render onto img1. The count should not matter.
 	for i := 0; i < 5; i++ {
 		vs := quadVertices(size, size, 0, 0, 1)
-		img1.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{img2}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
+		img1.DrawTriangles([graphics.ShaderSrcImageCount]*atlas.Image{img2}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
 		if got, want := img1.IsOnSourceBackendForTesting(), false; got != want {
 			t.Errorf("got: %v, want: %v", got, want)
 		}
@@ -203,7 +203,7 @@ func TestReputOnSourceBackend(t *testing.T) {
 	for i := 0; i < atlas.BaseCountToPutOnSourceBackend*2; i++ {
 		atlas.PutImagesOnSourceBackendForTesting(ui.Get().GraphicsDriverForTesting())
 		vs := quadVertices(size, size, 0, 0, 1)
-		img0.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{img1}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
+		img0.DrawTriangles([graphics.ShaderSrcImageCount]*atlas.Image{img1}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
 		if got, want := img1.IsOnSourceBackendForTesting(), false; got != want {
 			t.Errorf("got: %v, want: %v", got, want)
 		}
@@ -211,7 +211,7 @@ func TestReputOnSourceBackend(t *testing.T) {
 	// Finally, img1 is on a source backend.
 	atlas.PutImagesOnSourceBackendForTesting(ui.Get().GraphicsDriverForTesting())
 	vs := quadVertices(size, size, 0, 0, 1)
-	img0.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{img1}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
+	img0.DrawTriangles([graphics.ShaderSrcImageCount]*atlas.Image{img1}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
 	if got, want := img1.IsOnSourceBackendForTesting(), true; got != want {
 		t.Errorf("got: %v, want: %v", got, want)
 	}
@@ -240,7 +240,7 @@ func TestReputOnSourceBackend(t *testing.T) {
 	}
 
 	vs = quadVertices(size, size, 0, 0, 1)
-	img0.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{img1}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
+	img0.DrawTriangles([graphics.ShaderSrcImageCount]*atlas.Image{img1}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
 	if got, want := img1.IsOnSourceBackendForTesting(), true; got != want {
 		t.Errorf("got: %v, want: %v", got, want)
 	}
@@ -270,7 +270,7 @@ func TestReputOnSourceBackend(t *testing.T) {
 	// Use img1 as a render target again. The count should not matter.
 	for i := 0; i < 5; i++ {
 		vs := quadVertices(size, size, 0, 0, 1)
-		img1.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{img2}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
+		img1.DrawTriangles([graphics.ShaderSrcImageCount]*atlas.Image{img2}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
 		if got, want := img1.IsOnSourceBackendForTesting(), false; got != want {
 			t.Errorf("got: %v, want: %v", got, want)
 		}
@@ -282,7 +282,7 @@ func TestReputOnSourceBackend(t *testing.T) {
 		atlas.PutImagesOnSourceBackendForTesting(ui.Get().GraphicsDriverForTesting())
 		img1.WritePixels(make([]byte, 4*size*size), image.Rect(0, 0, size, size))
 		vs := quadVertices(size, size, 0, 0, 1)
-		img0.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{img1}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
+		img0.DrawTriangles([graphics.ShaderSrcImageCount]*atlas.Image{img1}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
 		if got, want := img1.IsOnSourceBackendForTesting(), false; got != want {
 			t.Errorf("got: %v, want: %v", got, want)
 		}
@@ -291,7 +291,7 @@ func TestReputOnSourceBackend(t *testing.T) {
 
 	// img1 is not on an atlas due to WritePixels.
 	vs = quadVertices(size, size, 0, 0, 1)
-	img0.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{img1}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
+	img0.DrawTriangles([graphics.ShaderSrcImageCount]*atlas.Image{img1}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
 	if got, want := img1.IsOnSourceBackendForTesting(), false; got != want {
 		t.Errorf("got: %v, want: %v", got, want)
 	}
@@ -300,7 +300,7 @@ func TestReputOnSourceBackend(t *testing.T) {
 	for i := 0; i < atlas.BaseCountToPutOnSourceBackend*2; i++ {
 		atlas.PutImagesOnSourceBackendForTesting(ui.Get().GraphicsDriverForTesting())
 		vs := quadVertices(size, size, 0, 0, 1)
-		img0.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{img3}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
+		img0.DrawTriangles([graphics.ShaderSrcImageCount]*atlas.Image{img3}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
 		if got, want := img3.IsOnSourceBackendForTesting(), false; got != want {
 			t.Errorf("got: %v, want: %v", got, want)
 		}
@@ -403,7 +403,7 @@ func TestWritePixelsAfterDrawTriangles(t *testing.T) {
 	vs := quadVertices(w, h, 0, 0, 1)
 	is := graphics.QuadIndices()
 	dr := image.Rect(0, 0, w, h)
-	dst.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{src}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
+	dst.DrawTriangles([graphics.ShaderSrcImageCount]*atlas.Image{src}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
 	dst.WritePixels(pix, image.Rect(0, 0, w, h))
 
 	pix = make([]byte, 4*w*h)
@@ -450,7 +450,7 @@ func TestSmallImages(t *testing.T) {
 	vs := quadVertices(w, h, 0, 0, 1)
 	is := graphics.QuadIndices()
 	dr := image.Rect(0, 0, w, h)
-	dst.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{src}, vs, is, graphicsdriver.BlendSourceOver, dr, [graphics.ShaderImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
+	dst.DrawTriangles([graphics.ShaderSrcImageCount]*atlas.Image{src}, vs, is, graphicsdriver.BlendSourceOver, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
 
 	pix = make([]byte, 4*w*h)
 	ok, err := dst.ReadPixels(ui.Get().GraphicsDriverForTesting(), pix, image.Rect(0, 0, w, h))
@@ -497,7 +497,7 @@ func TestLongImages(t *testing.T) {
 	vs := quadVertices(w, h, 0, 0, scale)
 	is := graphics.QuadIndices()
 	dr := image.Rect(0, 0, dstW, dstH)
-	dst.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{src}, vs, is, graphicsdriver.BlendSourceOver, dr, [graphics.ShaderImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
+	dst.DrawTriangles([graphics.ShaderSrcImageCount]*atlas.Image{src}, vs, is, graphicsdriver.BlendSourceOver, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
 
 	pix = make([]byte, 4*dstW*dstH)
 	ok, err := dst.ReadPixels(ui.Get().GraphicsDriverForTesting(), pix, image.Rect(0, 0, dstW, dstH))
@@ -613,7 +613,7 @@ func TestDeallocatedAndReputOnSourceBackend(t *testing.T) {
 	vs := quadVertices(size, size, 0, 0, 1)
 	is := graphics.QuadIndices()
 	dr := image.Rect(0, 0, size, size)
-	src.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{src2}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
+	src.DrawTriangles([graphics.ShaderSrcImageCount]*atlas.Image{src2}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
 	if got, want := src.IsOnSourceBackendForTesting(), false; got != want {
 		t.Errorf("got: %v, want: %v", got, want)
 	}
@@ -622,7 +622,7 @@ func TestDeallocatedAndReputOnSourceBackend(t *testing.T) {
 	for i := 0; i < atlas.BaseCountToPutOnSourceBackend/2; i++ {
 		atlas.PutImagesOnSourceBackendForTesting(ui.Get().GraphicsDriverForTesting())
 		vs := quadVertices(size, size, 0, 0, 1)
-		dst.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{src}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
+		dst.DrawTriangles([graphics.ShaderSrcImageCount]*atlas.Image{src}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
 		if got, want := src.IsOnSourceBackendForTesting(), false; got != want {
 			t.Errorf("got: %v, want: %v", got, want)
 		}
@@ -656,7 +656,7 @@ func TestImageIsNotReputOnSourceBackendWithoutUsingAsSource(t *testing.T) {
 	// Call DrawTriangles multiple times.
 	// The number of DrawTriangles doesn't matter as long as these are called in one frame.
 	for i := 0; i < 2; i++ {
-		src2.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{src}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
+		src2.DrawTriangles([graphics.ShaderSrcImageCount]*atlas.Image{src}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
 	}
 	if got, want := src2.IsOnSourceBackendForTesting(), false; got != want {
 		t.Errorf("got: %v, want: %v", got, want)
@@ -675,7 +675,7 @@ func TestImageIsNotReputOnSourceBackendWithoutUsingAsSource(t *testing.T) {
 	for i := 0; i < atlas.BaseCountToPutOnSourceBackend; i++ {
 		atlas.PutImagesOnSourceBackendForTesting(ui.Get().GraphicsDriverForTesting())
 		vs := quadVertices(size, size, 0, 0, 1)
-		dst.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{src2}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
+		dst.DrawTriangles([graphics.ShaderSrcImageCount]*atlas.Image{src2}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
 		if got, want := src2.IsOnSourceBackendForTesting(), false; got != want {
 			t.Errorf("got: %v, want: %v", got, want)
 		}
@@ -801,14 +801,14 @@ func TestDestinationCountOverflow(t *testing.T) {
 
 	// Use dst0 as a destination for a while.
 	for i := 0; i < 31; i++ {
-		dst0.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{src}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
+		dst0.DrawTriangles([graphics.ShaderSrcImageCount]*atlas.Image{src}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
 		atlas.PutImagesOnSourceBackendForTesting(ui.Get().GraphicsDriverForTesting())
 	}
 
 	// Use dst0 as a source for a while.
 	// As dst0 is used as a destination too many times (31 is a maximum), dst0's backend should never be a source backend.
 	for i := 0; i < 100; i++ {
-		dst1.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{dst0}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
+		dst1.DrawTriangles([graphics.ShaderSrcImageCount]*atlas.Image{dst0}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
 		atlas.PutImagesOnSourceBackendForTesting(ui.Get().GraphicsDriverForTesting())
 		if dst0.IsOnSourceBackendForTesting() {
 			t.Errorf("dst0 cannot be on a source backend: %d", i)
@@ -834,7 +834,7 @@ func TestIteratingImagesToPutOnSourceBackend(t *testing.T) {
 	is := graphics.QuadIndices()
 	dr := image.Rect(0, 0, w, h)
 	for _, img := range srcs {
-		img.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{src}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
+		img.DrawTriangles([graphics.ShaderSrcImageCount]*atlas.Image{src}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
 	}
 	atlas.PutImagesOnSourceBackendForTesting(ui.Get().GraphicsDriverForTesting())
 
@@ -842,7 +842,7 @@ func TestIteratingImagesToPutOnSourceBackend(t *testing.T) {
 	// Check iterating the registered image works correctly.
 	for i := 0; i < 100; i++ {
 		for _, src := range srcs {
-			dst.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{src}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
+			dst.DrawTriangles([graphics.ShaderSrcImageCount]*atlas.Image{src}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
 		}
 		atlas.PutImagesOnSourceBackendForTesting(ui.Get().GraphicsDriverForTesting())
 	}

internal/atlas/shader_test.go

@@ -37,12 +37,12 @@ func TestShaderFillTwice(t *testing.T) {
 	dr := image.Rect(0, 0, w, h)
 	g := ui.Get().GraphicsDriverForTesting()
 	s0 := atlas.NewShader(etesting.ShaderProgramFill(0xff, 0xff, 0xff, 0xff))
-	dst.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, s0, nil, graphicsdriver.FillAll)
+	dst.DrawTriangles([graphics.ShaderSrcImageCount]*atlas.Image{}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, s0, nil, graphicsdriver.FillAll)
 
 	// Vertices must be recreated (#1755)
 	vs = quadVertices(w, h, 0, 0, 1)
 	s1 := atlas.NewShader(etesting.ShaderProgramFill(0x80, 0x80, 0x80, 0xff))
-	dst.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, s1, nil, graphicsdriver.FillAll)
+	dst.DrawTriangles([graphics.ShaderSrcImageCount]*atlas.Image{}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, s1, nil, graphicsdriver.FillAll)
 
 	pix := make([]byte, 4*w*h)
 	ok, err := dst.ReadPixels(g, pix, image.Rect(0, 0, w, h))
@@ -69,11 +69,11 @@ func TestImageDrawTwice(t *testing.T) {
 	vs := quadVertices(w, h, 0, 0, 1)
 	is := graphics.QuadIndices()
 	dr := image.Rect(0, 0, w, h)
-	dst.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{src0}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
+	dst.DrawTriangles([graphics.ShaderSrcImageCount]*atlas.Image{src0}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
 
 	// Vertices must be recreated (#1755)
 	vs = quadVertices(w, h, 0, 0, 1)
-	dst.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{src1}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
+	dst.DrawTriangles([graphics.ShaderSrcImageCount]*atlas.Image{src1}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
 
 	pix := make([]byte, 4*w*h)
 	ok, err := dst.ReadPixels(ui.Get().GraphicsDriverForTesting(), pix, image.Rect(0, 0, w, h))
@@ -97,7 +97,7 @@ func TestGCShader(t *testing.T) {
 	vs := quadVertices(w, h, 0, 0, 1)
 	is := graphics.QuadIndices()
 	dr := image.Rect(0, 0, w, h)
-	dst.DrawTriangles([graphics.ShaderImageCount]*atlas.Image{}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderImageCount]image.Rectangle{}, s, nil, graphicsdriver.FillAll)
+	dst.DrawTriangles([graphics.ShaderSrcImageCount]*atlas.Image{}, vs, is, graphicsdriver.BlendCopy, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, s, nil, graphicsdriver.FillAll)
 
 	// Ensure other objects are GCed, as GC appends deferred functions for collected objects.
 	ensureGC()

internal/buffered/image.go

@@ -183,7 +183,7 @@ func (i *Image) WritePixels(pix []byte, region image.Rectangle) {
 // DrawTriangles draws the src image with the given vertices.
 //
 // Copying vertices and indices is the caller's responsibility.
-func (i *Image) DrawTriangles(srcs [graphics.ShaderImageCount]*Image, vertices []float32, indices []uint32, blend graphicsdriver.Blend, dstRegion image.Rectangle, srcRegions [graphics.ShaderImageCount]image.Rectangle, shader *atlas.Shader, uniforms []uint32, fillRule graphicsdriver.FillRule) {
+func (i *Image) DrawTriangles(srcs [graphics.ShaderSrcImageCount]*Image, vertices []float32, indices []uint32, blend graphicsdriver.Blend, dstRegion image.Rectangle, srcRegions [graphics.ShaderSrcImageCount]image.Rectangle, shader *atlas.Shader, uniforms []uint32, fillRule graphicsdriver.FillRule) {
 	for _, src := range srcs {
 		if i == src {
 			panic("buffered: Image.DrawTriangles: source images must be different from the receiver")
@@ -197,7 +197,7 @@ func (i *Image) DrawTriangles(srcs [graphics.ShaderImageCount]*Image, vertices [
 
 	i.syncPixelsIfNeeded()
 
-	var imgs [graphics.ShaderImageCount]*atlas.Image
+	var imgs [graphics.ShaderSrcImageCount]*atlas.Image
 	for i, img := range srcs {
 		if img == nil {
 			continue
@@ -211,6 +211,45 @@ func (i *Image) DrawTriangles(srcs [graphics.ShaderImageCount]*Image, vertices [
 	i.pixels = nil
 }
 
+func DrawTrianglesMRT(dsts [graphics.ShaderDstImageCount]*Image, srcs [graphics.ShaderSrcImageCount]*Image, vertices []float32, indices []uint32, blend graphicsdriver.Blend, dstRegion image.Rectangle, srcRegions [graphics.ShaderSrcImageCount]image.Rectangle, shader *atlas.Shader, uniforms []uint32, fillRule graphicsdriver.FillRule) {
+	for _, src := range srcs {
+		for _, dst := range dsts {
+			if dst == src {
+				panic("buffered: DrawTrianglesMRT: source images must be different from the destination")
+			}
+		}
+		if src != nil {
+			// src's pixels have to be synced between CPU and GPU,
+			// but doesn't have to be cleared since src is not modified in this function.
+			src.syncPixelsIfNeeded()
+		}
+	}
+
+	var dstImgs [graphics.ShaderDstImageCount]*atlas.Image
+	for i, dst := range dsts {
+		if dst == nil {
+			continue
+		}
+		dst.syncPixelsIfNeeded()
+		dstImgs[i] = dst.img
+	}
+
+	var srcImgs [graphics.ShaderSrcImageCount]*atlas.Image
+	for i, src := range srcs {
+		if src == nil {
+			continue
+		}
+		srcImgs[i] = src.img
+	}
+
+	atlas.DrawTrianglesMRT(dstImgs, srcImgs, vertices, indices, blend, dstRegion, srcRegions, shader, uniforms, fillRule)
+
+	// After rendering, the pixel cache is no longer valid.
+	for _, dst := range dsts {
+		dst.pixels = nil
+	}
+}
+
 // syncPixelsIfNeeded syncs the pixels between CPU and GPU.
 // After syncPixelsIfNeeded, dotsBuffer is cleared, but pixels might remain.
 func (i *Image) syncPixelsIfNeeded() {
@@ -289,10 +328,10 @@ func (i *Image) syncPixelsIfNeeded() {
 		idx++
 	}
 
-	srcs := [graphics.ShaderImageCount]*atlas.Image{whiteImage.img}
+	srcs := [graphics.ShaderSrcImageCount]*atlas.Image{whiteImage.img}
 	dr := image.Rect(0, 0, i.width, i.height)
 	blend := graphicsdriver.BlendCopy
-	i.img.DrawTriangles(srcs, vs, is, blend, dr, [graphics.ShaderImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
+	i.img.DrawTriangles(srcs, vs, is, blend, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
 
 	// TODO: Use clear if Go 1.21 is available.
 	for pos := range i.dotsBuffer {

internal/buffered/image_test.go

@@ -55,8 +55,8 @@ func TestUnsyncedPixels(t *testing.T) {
 	graphics.QuadVertices(vs, 0, 0, 16, 16, 1, 0, 0, 1, 0, 0, 1, 1, 1, 1)
 	is := graphics.QuadIndices()
 	dr := image.Rect(0, 0, 16, 16)
-	sr := [graphics.ShaderImageCount]image.Rectangle{image.Rect(0, 0, 16, 16)}
+	sr := [graphics.ShaderSrcImageCount]image.Rectangle{image.Rect(0, 0, 16, 16)}
-	dst.DrawTriangles([graphics.ShaderImageCount]*buffered.Image{src}, vs, is, graphicsdriver.BlendSourceOver, dr, sr, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
+	dst.DrawTriangles([graphics.ShaderSrcImageCount]*buffered.Image{src}, vs, is, graphicsdriver.BlendSourceOver, dr, sr, atlas.NearestFilterShader, nil, graphicsdriver.FillAll)
 
 	// Check the result is correct.
 	var got [4]byte

internal/graphics/shader.go

@@ -89,9 +89,9 @@ var __imageSrcRegionSizes [%[1]d]vec2
 func imageSrcRegionOnTexture() (vec2, vec2) {
 	return __imageSrcRegionOrigins[0], __imageSrcRegionSizes[0]
 }
-`, ShaderImageCount)
+`, ShaderSrcImageCount)
 
-	for i := 0; i < ShaderImageCount; i++ {
+	for i := 0; i < ShaderSrcImageCount; i++ {
 		shaderSuffix += fmt.Sprintf(`
 // imageSrc%[1]dOrigin returns the source image's region origin on its texture.
 // The unit is the source texture's pixel or texel.
@@ -179,7 +179,7 @@ func CompileShader(src []byte) (*shaderir.Program, error) {
 		vert = "__vertex"
 		frag = "Fragment"
 	)
-	ir, err := shader.Compile(buf.Bytes(), vert, frag, ShaderImageCount)
+	ir, err := shader.Compile(buf.Bytes(), vert, frag, ShaderSrcImageCount)
 	if err != nil {
 		return nil, err
 	}

internal/graphics/vertex.go

@@ -15,7 +15,8 @@
 package graphics
 
 const (
-	ShaderImageCount = 4
+	ShaderSrcImageCount = 4
+	ShaderDstImageCount = 4
 
 	// PreservedUniformVariablesCount represents the number of preserved uniform variables.
 	// Any shaders in Ebitengine must have these uniform variables.
@@ -30,11 +31,11 @@ const (
 	ProjectionMatrixUniformVariableIndex = 6
 
 	PreservedUniformUint32Count = 2 + // the destination texture size
-		2*ShaderImageCount + // the source texture sizes array
+		2*ShaderSrcImageCount + // the source texture sizes array
 		2 + // the destination image region origin
 		2 + // the destination image region size
-		2*ShaderImageCount + // the source image region origins array
+		2*ShaderSrcImageCount + // the source image region origins array
-		2*ShaderImageCount + // the source image region sizes array
+		2*ShaderSrcImageCount + // the source image region sizes array
 		16 // the projection matrix
 )
 

internal/graphicscommand/command.go

@@ -61,8 +61,8 @@ func (p *drawTrianglesCommandPool) put(v *drawTrianglesCommand) {
 
 // drawTrianglesCommand represents a drawing command to draw an image on another image.
 type drawTrianglesCommand struct {
-	dst        *Image
+	dsts       [graphics.ShaderDstImageCount]*Image
-	srcs       [graphics.ShaderImageCount]*Image
+	srcs       [graphics.ShaderSrcImageCount]*Image
 	vertices   []float32
 	blend      graphicsdriver.Blend
 	dstRegions []graphicsdriver.DstRegion
@@ -81,12 +81,19 @@ func (c *drawTrianglesCommand) String() string {
 		c.blend.BlendOperationRGB,
 		c.blend.BlendOperationAlpha)
 
-	dst := fmt.Sprintf("%d", c.dst.id)
+	var dststrs [graphics.ShaderDstImageCount]string
-	if c.dst.screen {
+	for i, dst := range c.dsts {
-		dst += " (screen)"
+		if dst == nil {
+			dststrs[i] = "(nil)"
+			continue
+		}
+		dststrs[i] = fmt.Sprintf("%d", dst.id)
+		if dst.screen {
+			dststrs[i] += " (screen)"
+		}
 	}
 
-	var srcstrs [graphics.ShaderImageCount]string
+	var srcstrs [graphics.ShaderSrcImageCount]string
 	for i, src := range c.srcs {
 		if src == nil {
 			srcstrs[i] = "(nil)"
@@ -98,7 +105,7 @@ func (c *drawTrianglesCommand) String() string {
 		}
 	}
 
-	return fmt.Sprintf("draw-triangles: dst: %s <- src: [%s], num of dst regions: %d, num of indices: %d, blend: %s, fill rule: %s, shader id: %d", dst, strings.Join(srcstrs[:], ", "), len(c.dstRegions), c.numIndices(), blend, c.fillRule, c.shader.id)
+	return fmt.Sprintf("draw-triangles: dst: [%s] <- src: [%s], num of dst regions: %d, num of indices: %d, blend: %s, fill rule: %s, shader id: %d", strings.Join(dststrs[:], ", "), strings.Join(srcstrs[:], ", "), len(c.dstRegions), c.numIndices(), blend, c.fillRule, c.shader.id)
 }
 
 // Exec executes the drawTrianglesCommand.
@@ -108,16 +115,25 @@ func (c *drawTrianglesCommand) Exec(commandQueue *commandQueue, graphicsDriver g
 		return nil
 	}
 
-	var imgs [graphics.ShaderImageCount]graphicsdriver.ImageID
+	var dsts [graphics.ShaderDstImageCount]graphicsdriver.ImageID
-	for i, src := range c.srcs {
+	for i, dst := range c.dsts {
-		if src == nil {
+		if dst == nil {
-			imgs[i] = graphicsdriver.InvalidImageID
+			dsts[i] = graphicsdriver.InvalidImageID
 			continue
 		}
-		imgs[i] = src.image.ID()
+		dsts[i] = dst.image.ID()
 	}
 
-	return graphicsDriver.DrawTriangles(c.dst.image.ID(), imgs, c.shader.shader.ID(), c.dstRegions, indexOffset, c.blend, c.uniforms, c.fillRule)
+	var srcs [graphics.ShaderSrcImageCount]graphicsdriver.ImageID
+	for i, src := range c.srcs {
+		if src == nil {
+			srcs[i] = graphicsdriver.InvalidImageID
+			continue
+		}
+		srcs[i] = src.image.ID()
+	}
+
+	return graphicsDriver.DrawTriangles(dsts, srcs, c.shader.shader.ID(), c.dstRegions, indexOffset, c.blend, c.uniforms, c.fillRule)
 }
 
 func (c *drawTrianglesCommand) NeedsSync() bool {
@@ -142,7 +158,7 @@ func (c *drawTrianglesCommand) setVertices(vertices []float32) {
 
 // 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.ShaderImageCount]*Image, vertices []float32, blend graphicsdriver.Blend, shader *Shader, uniforms []uint32, fillRule graphicsdriver.FillRule) bool {
+func (c *drawTrianglesCommand) CanMergeWithDrawTrianglesCommand(dsts [graphics.ShaderDstImageCount]*Image, srcs [graphics.ShaderSrcImageCount]*Image, vertices []float32, blend graphicsdriver.Blend, shader *Shader, uniforms []uint32, fillRule graphicsdriver.FillRule) bool {
 	if c.shader != shader {
 		return false
 	}
@@ -154,7 +170,7 @@ func (c *drawTrianglesCommand) CanMergeWithDrawTrianglesCommand(dst *Image, srcs
 			return false
 		}
 	}
-	if c.dst != dst {
+	if c.dsts != dsts {
 		return false
 	}
 	if c.srcs != srcs {

internal/graphicscommand/commandqueue.go

@@ -105,7 +105,7 @@ func mustUseDifferentVertexBuffer(nextNumVertexFloats int) bool {
 }
 
 // EnqueueDrawTrianglesCommand enqueues a drawing-image command.
-func (q *commandQueue) EnqueueDrawTrianglesCommand(dst *Image, srcs [graphics.ShaderImageCount]*Image, vertices []float32, indices []uint32, blend graphicsdriver.Blend, dstRegion image.Rectangle, srcRegions [graphics.ShaderImageCount]image.Rectangle, shader *Shader, uniforms []uint32, fillRule graphicsdriver.FillRule) {
+func (q *commandQueue) EnqueueDrawTrianglesCommand(dsts [graphics.ShaderDstImageCount]*Image, srcs [graphics.ShaderSrcImageCount]*Image, vertices []float32, indices []uint32, blend graphicsdriver.Blend, dstRegion image.Rectangle, srcRegions [graphics.ShaderSrcImageCount]image.Rectangle, shader *Shader, uniforms []uint32, fillRule graphicsdriver.FillRule) {
 	if len(vertices) > maxVertexFloatCount {
 		panic(fmt.Sprintf("graphicscommand: len(vertices) must equal to or less than %d but was %d", maxVertexFloatCount, len(vertices)))
 	}
@@ -125,7 +125,7 @@ func (q *commandQueue) EnqueueDrawTrianglesCommand(dst *Image, srcs [graphics.Sh
 	// prependPreservedUniforms not only prepends values to the given slice but also creates a new slice.
 	// Allocating a new slice is necessary to make EnqueueDrawTrianglesCommand safe so far.
 	// TODO: This might cause a performance issue (#2601).
-	uniforms = q.prependPreservedUniforms(uniforms, shader, dst, srcs, dstRegion, srcRegions)
+	uniforms = q.prependPreservedUniforms(uniforms, shader, dsts, srcs, dstRegion, srcRegions)
 
 	// Remove unused uniform variables so that more commands can be merged.
 	shader.ir.FilterUniformVariables(uniforms)
@@ -133,7 +133,7 @@ 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) {
 		if last, ok := q.commands[len(q.commands)-1].(*drawTrianglesCommand); ok {
-			if last.CanMergeWithDrawTrianglesCommand(dst, srcs, vertices, blend, shader, uniforms, fillRule) {
+			if last.CanMergeWithDrawTrianglesCommand(dsts, srcs, vertices, blend, shader, uniforms, fillRule) {
 				last.setVertices(q.lastVertices(len(vertices) + last.numVertices()))
 				if last.dstRegions[len(last.dstRegions)-1].Region == dstRegion {
 					last.dstRegions[len(last.dstRegions)-1].IndexCount += len(indices)
@@ -149,7 +149,7 @@ func (q *commandQueue) EnqueueDrawTrianglesCommand(dst *Image, srcs [graphics.Sh
 	}
 
 	c := q.drawTrianglesCommandPool.get()
-	c.dst = dst
+	c.dsts = dsts
 	c.srcs = srcs
 	c.vertices = q.lastVertices(len(vertices))
 	c.blend = blend
@@ -324,18 +324,18 @@ func imageRectangleToRectangleF32(r image.Rectangle) rectangleF32 {
 	}
 }
 
-func (q *commandQueue) prependPreservedUniforms(uniforms []uint32, shader *Shader, dst *Image, srcs [graphics.ShaderImageCount]*Image, dstRegion image.Rectangle, srcRegions [graphics.ShaderImageCount]image.Rectangle) []uint32 {
+func (q *commandQueue) prependPreservedUniforms(uniforms []uint32, shader *Shader, dsts [graphics.ShaderDstImageCount]*Image, srcs [graphics.ShaderSrcImageCount]*Image, dstRegion image.Rectangle, srcRegions [graphics.ShaderSrcImageCount]image.Rectangle) []uint32 {
 	origUniforms := uniforms
 	uniforms = q.uint32sBuffer.alloc(len(origUniforms) + graphics.PreservedUniformUint32Count)
 	copy(uniforms[graphics.PreservedUniformUint32Count:], origUniforms)
 
 	// Set the destination texture size.
-	dw, dh := dst.InternalSize()
+	dw, dh := dsts[0].InternalSize()
 	uniforms[0] = math.Float32bits(float32(dw))
 	uniforms[1] = math.Float32bits(float32(dh))
 	uniformIndex := 2
 
-	for i := 0; i < graphics.ShaderImageCount; i++ {
+	for i := 0; i < graphics.ShaderSrcImageCount; i++ {
 		var floatW, floatH uint32
 		if srcs[i] != nil {
 			w, h := srcs[i].InternalSize()
@@ -346,7 +346,7 @@ func (q *commandQueue) prependPreservedUniforms(uniforms []uint32, shader *Shade
 		uniforms[uniformIndex+i*2] = floatW
 		uniforms[uniformIndex+1+i*2] = floatH
 	}
-	uniformIndex += graphics.ShaderImageCount * 2
+	uniformIndex += graphics.ShaderSrcImageCount * 2
 
 	dr := imageRectangleToRectangleF32(dstRegion)
 	if shader.unit() == shaderir.Texels {
@@ -366,7 +366,7 @@ func (q *commandQueue) prependPreservedUniforms(uniforms []uint32, shader *Shade
 	uniforms[uniformIndex+1] = math.Float32bits(dr.height)
 	uniformIndex += 2
 
-	var srs [graphics.ShaderImageCount]rectangleF32
+	var srs [graphics.ShaderSrcImageCount]rectangleF32
 	for i, r := range srcRegions {
 		srs[i] = imageRectangleToRectangleF32(r)
 	}
@@ -384,18 +384,18 @@ func (q *commandQueue) prependPreservedUniforms(uniforms []uint32, shader *Shade
 	}
 
 	// Set the source region origins.
-	for i := 0; i < graphics.ShaderImageCount; i++ {
+	for i := 0; i < graphics.ShaderSrcImageCount; i++ {
 		uniforms[uniformIndex+i*2] = math.Float32bits(srs[i].x)
 		uniforms[uniformIndex+1+i*2] = math.Float32bits(srs[i].y)
 	}
-	uniformIndex += graphics.ShaderImageCount * 2
+	uniformIndex += graphics.ShaderSrcImageCount * 2
 
 	// Set the source region sizes.
-	for i := 0; i < graphics.ShaderImageCount; i++ {
+	for i := 0; i < graphics.ShaderSrcImageCount; i++ {
 		uniforms[uniformIndex+i*2] = math.Float32bits(srs[i].width)
 		uniforms[uniformIndex+1+i*2] = math.Float32bits(srs[i].height)
 	}
-	uniformIndex += graphics.ShaderImageCount * 2
+	uniformIndex += graphics.ShaderSrcImageCount * 2
 
 	// Set the projection matrix.
 	uniforms[uniformIndex] = math.Float32bits(2 / float32(dw))
@@ -469,11 +469,11 @@ func (c *commandQueueManager) putCommandQueue(commandQueue *commandQueue) {
 	c.pool.put(commandQueue)
 }
 
-func (c *commandQueueManager) enqueueDrawTrianglesCommand(dst *Image, srcs [graphics.ShaderImageCount]*Image, vertices []float32, indices []uint32, blend graphicsdriver.Blend, dstRegion image.Rectangle, srcRegions [graphics.ShaderImageCount]image.Rectangle, shader *Shader, uniforms []uint32, fillRule graphicsdriver.FillRule) {
+func (c *commandQueueManager) enqueueDrawTrianglesCommand(dsts [graphics.ShaderDstImageCount]*Image, srcs [graphics.ShaderSrcImageCount]*Image, vertices []float32, indices []uint32, blend graphicsdriver.Blend, dstRegion image.Rectangle, srcRegions [graphics.ShaderSrcImageCount]image.Rectangle, shader *Shader, uniforms []uint32, fillRule graphicsdriver.FillRule) {
 	if c.current == nil {
 		c.current, _ = c.pool.get()
 	}
-	c.current.EnqueueDrawTrianglesCommand(dst, srcs, vertices, indices, blend, dstRegion, srcRegions, shader, uniforms, fillRule)
+	c.current.EnqueueDrawTrianglesCommand(dsts, srcs, vertices, indices, blend, dstRegion, srcRegions, shader, uniforms, fillRule)
 }
 
 func (c *commandQueueManager) flush(graphicsDriver graphicsdriver.Graphics, endFrame bool) error {

internal/graphicscommand/image.go

@@ -130,7 +130,7 @@ 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.ShaderImageCount]*Image, vertices []float32, indices []uint32, blend graphicsdriver.Blend, dstRegion image.Rectangle, srcRegions [graphics.ShaderImageCount]image.Rectangle, shader *Shader, uniforms []uint32, fillRule graphicsdriver.FillRule) {
+func (i *Image) DrawTriangles(srcs [graphics.ShaderSrcImageCount]*Image, vertices []float32, indices []uint32, blend graphicsdriver.Blend, dstRegion image.Rectangle, srcRegions [graphics.ShaderSrcImageCount]image.Rectangle, shader *Shader, uniforms []uint32, fillRule graphicsdriver.FillRule) {
 	for _, src := range srcs {
 		if src == nil {
 			continue
@@ -142,7 +142,45 @@ func (i *Image) DrawTriangles(srcs [graphics.ShaderImageCount]*Image, vertices [
 	}
 	i.flushBufferedWritePixels()
 
-	theCommandQueueManager.enqueueDrawTrianglesCommand(i, srcs, vertices, indices, blend, dstRegion, srcRegions, shader, uniforms, fillRule)
+	theCommandQueueManager.enqueueDrawTrianglesCommand([graphics.ShaderDstImageCount]*Image{i}, srcs, vertices, indices, blend, dstRegion, srcRegions, shader, uniforms, fillRule)
+}
+
+// DrawTriangles draws triangles with the given image.
+//
+// The vertex floats are:
+//
+//	0: Destination X in pixels
+//	1: Destination Y in pixels
+//	2: Source X in texels
+//	3: Source Y in texels
+//	4: Color R [0.0-1.0]
+//	5: Color G
+//	6: Color B
+//	7: Color Y
+//
+// src and shader are exclusive and only either is non-nil.
+//
+// The elements that index is in between 2 and 7 are used for the source images.
+// The source image is 1) src argument if non-nil, or 2) an image value in the uniform variables if it exists.
+// If there are multiple images in the uniform variables, the smallest ID's value is adopted.
+//
+// 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 DrawTrianglesMRT(dsts [graphics.ShaderDstImageCount]*Image, srcs [graphics.ShaderSrcImageCount]*Image, vertices []float32, indices []uint32, blend graphicsdriver.Blend, dstRegion image.Rectangle, srcRegions [graphics.ShaderSrcImageCount]image.Rectangle, shader *Shader, uniforms []uint32, fillRule graphicsdriver.FillRule) {
+	for _, src := range srcs {
+		if src == nil {
+			continue
+		}
+		if src.screen {
+			panic("graphicscommand: the screen image cannot be the rendering des")
+		}
+		src.flushBufferedWritePixels()
+	}
+	for _, dst := range dsts {
+		dst.flushBufferedWritePixels()
+	}
+
+	theCommandQueueManager.enqueueDrawTrianglesCommand(dsts, srcs, vertices, indices, blend, dstRegion, srcRegions, shader, uniforms, fillRule)
 }
 
 // ReadPixels reads the image's pixels.

internal/graphicscommand/image_test.go

@@ -59,7 +59,7 @@ func TestClear(t *testing.T) {
 	vs := quadVertices(w/2, h/2)
 	is := graphics.QuadIndices()
 	dr := image.Rect(0, 0, w, h)
-	dst.DrawTriangles([graphics.ShaderImageCount]*graphicscommand.Image{src}, vs, is, graphicsdriver.BlendClear, dr, [graphics.ShaderImageCount]image.Rectangle{}, nearestFilterShader, nil, graphicsdriver.FillAll)
+	dst.DrawTriangles([graphics.ShaderSrcImageCount]*graphicscommand.Image{src}, vs, is, graphicsdriver.BlendClear, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, nearestFilterShader, nil, graphicsdriver.FillAll)
 
 	pix := make([]byte, 4*w*h)
 	if err := dst.ReadPixels(ui.Get().GraphicsDriverForTesting(), []graphicsdriver.PixelsArgs{
@@ -90,8 +90,8 @@ func TestWritePixelsPartAfterDrawTriangles(t *testing.T) {
 	vs := quadVertices(w/2, h/2)
 	is := graphics.QuadIndices()
 	dr := image.Rect(0, 0, w, h)
-	dst.DrawTriangles([graphics.ShaderImageCount]*graphicscommand.Image{clr}, vs, is, graphicsdriver.BlendClear, dr, [graphics.ShaderImageCount]image.Rectangle{}, nearestFilterShader, nil, graphicsdriver.FillAll)
+	dst.DrawTriangles([graphics.ShaderSrcImageCount]*graphicscommand.Image{clr}, vs, is, graphicsdriver.BlendClear, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, nearestFilterShader, nil, graphicsdriver.FillAll)
-	dst.DrawTriangles([graphics.ShaderImageCount]*graphicscommand.Image{src}, vs, is, graphicsdriver.BlendSourceOver, dr, [graphics.ShaderImageCount]image.Rectangle{}, nearestFilterShader, nil, graphicsdriver.FillAll)
+	dst.DrawTriangles([graphics.ShaderSrcImageCount]*graphicscommand.Image{src}, vs, is, graphicsdriver.BlendSourceOver, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, nearestFilterShader, nil, graphicsdriver.FillAll)
 	bs := graphics.NewManagedBytes(4, func(bs []byte) {
 		for i := range bs {
 			bs[i] = 0
@@ -109,11 +109,11 @@ func TestShader(t *testing.T) {
 	vs := quadVertices(w, h)
 	is := graphics.QuadIndices()
 	dr := image.Rect(0, 0, w, h)
-	dst.DrawTriangles([graphics.ShaderImageCount]*graphicscommand.Image{clr}, vs, is, graphicsdriver.BlendClear, dr, [graphics.ShaderImageCount]image.Rectangle{}, nearestFilterShader, nil, graphicsdriver.FillAll)
+	dst.DrawTriangles([graphics.ShaderSrcImageCount]*graphicscommand.Image{clr}, vs, is, graphicsdriver.BlendClear, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, nearestFilterShader, nil, graphicsdriver.FillAll)
 
 	g := ui.Get().GraphicsDriverForTesting()
 	s := graphicscommand.NewShader(etesting.ShaderProgramFill(0xff, 0, 0, 0xff))
-	dst.DrawTriangles([graphics.ShaderImageCount]*graphicscommand.Image{}, vs, is, graphicsdriver.BlendSourceOver, dr, [graphics.ShaderImageCount]image.Rectangle{}, s, nil, graphicsdriver.FillAll)
+	dst.DrawTriangles([graphics.ShaderSrcImageCount]*graphicscommand.Image{}, vs, is, graphicsdriver.BlendSourceOver, dr, [graphics.ShaderSrcImageCount]image.Rectangle{}, s, nil, graphicsdriver.FillAll)
 
 	pix := make([]byte, 4*w*h)
 	if err := dst.ReadPixels(g, []graphicsdriver.PixelsArgs{

internal/graphicsdriver/directx/graphics11_windows.go

@@ -515,14 +515,14 @@ func (g *graphics11) removeShader(s *shader11) {
 	delete(g.shaders, s.id)
 }
 
-func (g *graphics11) DrawTriangles(dstID graphicsdriver.ImageID, srcIDs [graphics.ShaderImageCount]graphicsdriver.ImageID, shaderID graphicsdriver.ShaderID, dstRegions []graphicsdriver.DstRegion, indexOffset int, blend graphicsdriver.Blend, uniforms []uint32, fillRule graphicsdriver.FillRule) error {
+func (g *graphics11) DrawTriangles(dstIDs [graphics.ShaderDstImageCount]graphicsdriver.ImageID, srcIDs [graphics.ShaderSrcImageCount]graphicsdriver.ImageID, shaderID graphicsdriver.ShaderID, dstRegions []graphicsdriver.DstRegion, indexOffset int, blend graphicsdriver.Blend, uniforms []uint32, fillRule graphicsdriver.FillRule) error {
 	// Remove bound textures first. This is needed to avoid warnings on the debugger.
 	g.deviceContext.OMSetRenderTargets([]*_ID3D11RenderTargetView{nil}, nil)
-	srvs := [graphics.ShaderImageCount]*_ID3D11ShaderResourceView{}
+	srvs := [graphics.ShaderSrcImageCount]*_ID3D11ShaderResourceView{}
 	g.deviceContext.PSSetShaderResources(0, srvs[:])
 
-	dst := g.images[dstID]
+	dst := g.images[dstIDs[0]] // TODO: handle array
-	var srcs [graphics.ShaderImageCount]*image11
+	var srcs [graphics.ShaderSrcImageCount]*image11
 	for i, id := range srcIDs {
 		img := g.images[id]
 		if img == nil {

internal/graphicsdriver/directx/graphics12_windows.go

@@ -1082,7 +1082,7 @@ func (g *graphics12) NewShader(program *shaderir.Program) (graphicsdriver.Shader
 	return s, nil
 }
 
-func (g *graphics12) DrawTriangles(dstID graphicsdriver.ImageID, srcs [graphics.ShaderImageCount]graphicsdriver.ImageID, shaderID graphicsdriver.ShaderID, dstRegions []graphicsdriver.DstRegion, indexOffset int, blend graphicsdriver.Blend, uniforms []uint32, fillRule graphicsdriver.FillRule) error {
+func (g *graphics12) DrawTriangles(dstIDs [graphics.ShaderDstImageCount]graphicsdriver.ImageID, srcs [graphics.ShaderSrcImageCount]graphicsdriver.ImageID, shaderID graphicsdriver.ShaderID, dstRegions []graphicsdriver.DstRegion, indexOffset int, blend graphicsdriver.Blend, uniforms []uint32, fillRule graphicsdriver.FillRule) error {
 	if shaderID == graphicsdriver.InvalidShaderID {
 		return fmt.Errorf("directx: shader ID is invalid")
 	}
@@ -1103,13 +1103,13 @@ func (g *graphics12) DrawTriangles(dstID graphicsdriver.ImageID, srcs [graphics.
 		g.pipelineStates.releaseConstantBuffers(g.frameIndex)
 	}
 
-	dst := g.images[dstID]
+	dst := g.images[dstIDs[0]] // TODO: handle array
 	var resourceBarriers []_D3D12_RESOURCE_BARRIER_Transition
 	if rb, ok := dst.transiteState(_D3D12_RESOURCE_STATE_RENDER_TARGET); ok {
 		resourceBarriers = append(resourceBarriers, rb)
 	}
 
-	var srcImages [graphics.ShaderImageCount]*image12
+	var srcImages [graphics.ShaderSrcImageCount]*image12
 	for i, srcID := range srcs {
 		src := g.images[srcID]
 		if src == nil {

internal/graphicsdriver/directx/pipeline12_windows.go

@@ -128,7 +128,7 @@ type pipelineStates struct {
 	constantBufferMaps [frameCount][]uintptr
 }
 
-const numConstantBufferAndSourceTextures = 1 + graphics.ShaderImageCount
+const numConstantBufferAndSourceTextures = 1 + graphics.ShaderSrcImageCount
 
 func (p *pipelineStates) initialize(device *_ID3D12Device) (ferr error) {
 	// Create a CBV/SRV/UAV descriptor heap.
@@ -180,7 +180,7 @@ func (p *pipelineStates) initialize(device *_ID3D12Device) (ferr error) {
 	return nil
 }
 
-func (p *pipelineStates) drawTriangles(device *_ID3D12Device, commandList *_ID3D12GraphicsCommandList, frameIndex int, screen bool, srcs [graphics.ShaderImageCount]*image12, shader *shader12, dstRegions []graphicsdriver.DstRegion, uniforms []uint32, blend graphicsdriver.Blend, indexOffset int, fillRule graphicsdriver.FillRule) error {
+func (p *pipelineStates) drawTriangles(device *_ID3D12Device, commandList *_ID3D12GraphicsCommandList, frameIndex int, screen bool, srcs [graphics.ShaderSrcImageCount]*image12, shader *shader12, dstRegions []graphicsdriver.DstRegion, uniforms []uint32, blend graphicsdriver.Blend, indexOffset int, fillRule graphicsdriver.FillRule) error {
 	idx := len(p.constantBuffers[frameIndex])
 	if idx >= numDescriptorsPerFrame {
 		return fmt.Errorf("directx: too many constant buffers")
@@ -354,7 +354,7 @@ func (p *pipelineStates) ensureRootSignature(device *_ID3D12Device) (rootSignatu
 	}
 	srv := _D3D12_DESCRIPTOR_RANGE{
 		RangeType:                         _D3D12_DESCRIPTOR_RANGE_TYPE_SRV, // t0
-		NumDescriptors:                    graphics.ShaderImageCount,
+		NumDescriptors:                    graphics.ShaderSrcImageCount,
 		BaseShaderRegister:                0,
 		RegisterSpace:                     0,
 		OffsetInDescriptorsFromTableStart: 1,

internal/graphicsdriver/directx/shader11_windows.go

@@ -78,7 +78,7 @@ func (s *shader11) disposeImpl() {
 	}
 }
 
-func (s *shader11) use(uniforms []uint32, srcs [graphics.ShaderImageCount]*image11) error {
+func (s *shader11) use(uniforms []uint32, srcs [graphics.ShaderSrcImageCount]*image11) error {
 	vs, err := s.ensureVertexShader()
 	if err != nil {
 		return err
@@ -114,7 +114,7 @@ func (s *shader11) use(uniforms []uint32, srcs [graphics.ShaderImageCount]*image
 	s.graphics.deviceContext.Unmap(unsafe.Pointer(cb), 0)
 
 	// Set the render sources.
-	var srvs [graphics.ShaderImageCount]*_ID3D11ShaderResourceView
+	var srvs [graphics.ShaderSrcImageCount]*_ID3D11ShaderResourceView
 	for i, src := range srcs {
 		if src == nil {
 			continue

internal/graphicsdriver/graphics.go

@@ -68,7 +68,7 @@ type Graphics interface {
 	NewShader(program *shaderir.Program) (Shader, error)
 
 	// DrawTriangles draws an image onto another image with the given parameters.
-	DrawTriangles(dst ImageID, srcs [graphics.ShaderImageCount]ImageID, shader ShaderID, dstRegions []DstRegion, indexOffset int, blend Blend, uniforms []uint32, fillRule FillRule) error
+	DrawTriangles(dsts [graphics.ShaderDstImageCount]ImageID, srcs [graphics.ShaderSrcImageCount]ImageID, shader ShaderID, dstRegions []DstRegion, indexOffset int, blend Blend, uniforms []uint32, fillRule FillRule) error
 }
 
 type Resetter interface {

internal/graphicsdriver/opengl/gl/debug.go

@@ -293,6 +293,14 @@ func (d *DebugContext) DisableVertexAttribArray(arg0 uint32) {
 	}
 }
 
+func (d *DebugContext) DrawBuffers(arg0 []uint32) {
+	d.Context.DrawBuffers(arg0)
+	fmt.Fprintln(os.Stderr, "DrawBuffers")
+	if e := d.Context.GetError(); e != NO_ERROR {
+		panic(fmt.Sprintf("gl: GetError() returned %d at DrawBuffers", e))
+	}
+}
+
 func (d *DebugContext) DrawElements(arg0 uint32, arg1 int32, arg2 uint32, arg3 int) {
 	d.Context.DrawElements(arg0, arg1, arg2, arg3)
 	fmt.Fprintln(os.Stderr, "DrawElements")

internal/graphicsdriver/opengl/gl/default_purego.go

@@ -51,6 +51,7 @@ type defaultContext struct {
 	gpDeleteVertexArrays       uintptr
 	gpDisable                  uintptr
 	gpDisableVertexAttribArray uintptr
+	gpDrawBuffers              uintptr
 	gpDrawElements             uintptr
 	gpEnable                   uintptr
 	gpEnableVertexAttribArray  uintptr
@@ -269,6 +270,10 @@ func (c *defaultContext) DrawElements(mode uint32, count int32, xtype uint32, of
 	purego.SyscallN(c.gpDrawElements, uintptr(mode), uintptr(count), uintptr(xtype), uintptr(offset))
 }
 
+func (c *defaultContext) DrawBuffers(buffers []uint32) {
+	purego.SyscallN(c.gpDrawBuffers, uintptr(len(buffers)), uintptr(unsafe.Pointer(&buffers[0])))
+}
+
 func (c *defaultContext) Enable(cap uint32) {
 	purego.SyscallN(c.gpEnable, uintptr(cap))
 }
@@ -501,6 +506,7 @@ func (c *defaultContext) LoadFunctions() error {
 	c.gpDeleteVertexArrays = g.get("glDeleteVertexArrays")
 	c.gpDisable = g.get("glDisable")
 	c.gpDisableVertexAttribArray = g.get("glDisableVertexAttribArray")
+	c.gpDrawBuffers = g.get("glDrawBuffers")
 	c.gpDrawElements = g.get("glDrawElements")
 	c.gpEnable = g.get("glEnable")
 	c.gpEnableVertexAttribArray = g.get("glEnableVertexAttribArray")

internal/graphicsdriver/opengl/gl/interface.go

@@ -60,6 +60,7 @@ type Context interface {
 	Disable(cap uint32)
 	DisableVertexAttribArray(index uint32)
 	DrawElements(mode uint32, count int32, xtype uint32, offset int)
+	DrawBuffers(buffers []uint32)
 	Enable(cap uint32)
 	EnableVertexAttribArray(index uint32)
 	Flush()

internal/graphicsdriver/opengl/graphics.go

@@ -45,8 +45,9 @@ type Graphics struct {
 	// drawCalled is true just after Draw is called. This holds true until WritePixels is called.
 	drawCalled bool
 
-	uniformVariableNameCache map[int]string
+	uniformVariableNameCache     map[int]string
-	textureVariableNameCache map[int]string
+	textureVariableNameCache     map[int]string
+	colorBufferVariableNameCache map[int]string
 
 	uniformVars []uniformVariable
 
@@ -198,18 +199,47 @@ func (g *Graphics) uniformVariableName(idx int) string {
 	return name
 }
 
-func (g *Graphics) DrawTriangles(dstID graphicsdriver.ImageID, srcIDs [graphics.ShaderImageCount]graphicsdriver.ImageID, shaderID graphicsdriver.ShaderID, dstRegions []graphicsdriver.DstRegion, indexOffset int, blend graphicsdriver.Blend, uniforms []uint32, fillRule graphicsdriver.FillRule) error {
+func (g *Graphics) DrawTriangles(dstIDs [graphics.ShaderDstImageCount]graphicsdriver.ImageID, srcIDs [graphics.ShaderSrcImageCount]graphicsdriver.ImageID, shaderID graphicsdriver.ShaderID, dstRegions []graphicsdriver.DstRegion, indexOffset int, blend graphicsdriver.Blend, uniforms []uint32, fillRule graphicsdriver.FillRule) error {
 	if shaderID == graphicsdriver.InvalidShaderID {
 		return fmt.Errorf("opengl: shader ID is invalid")
 	}
 
-	destination := g.images[dstID]
-
 	g.drawCalled = true
 
-	if err := destination.setViewport(); err != nil {
+	dstCount := 0
-		return err
+	var destinations [graphics.ShaderDstImageCount]*Image
+	for i, dstID := range dstIDs {
+		if dstID == graphicsdriver.InvalidImageID {
+			continue
+		}
+		dst := g.images[dstIDs[i]]
+		if dst == nil {
+			continue
+		}
+		if err := dst.setViewport(); err != nil {
+			return err
+		}
+		destinations[i] = dst
+		dstCount++
 	}
+	if dstCount == 0 {
+		return nil
+	}
+
+	// Color attachments
+	var attached []uint32
+	for i, dst := range destinations {
+		if dst == nil {
+			continue
+		}
+		if dstCount > 1 {
+			//fmt.Println("id:", dst.texture, "ok:", dst.id, "regions:", len(dstRegions))
+		}
+		attached = append(attached, uint32(gl.COLOR_ATTACHMENT0+i))
+		g.context.ctx.FramebufferTexture2D(gl.FRAMEBUFFER, uint32(gl.COLOR_ATTACHMENT0+i), gl.TEXTURE_2D, uint32(dst.texture), 0)
+	}
+	g.context.ctx.DrawBuffers(attached)
+
 	g.context.blend(blend)
 
 	shader := g.shaders[shaderID]
@@ -232,7 +262,7 @@ func (g *Graphics) DrawTriangles(dstID graphicsdriver.ImageID, srcIDs [graphics.
 	}
 
 	// In OpenGL, the NDC's Y direction is upward, so flip the Y direction for the final framebuffer.
-	if destination.screen {
+	if dstCount == 1 && destinations[0] != nil && destinations[0].screen {
 		const idx = graphics.ProjectionMatrixUniformVariableIndex
 		// Invert the sign bits as float32 values.
 		g.uniformVars[idx].value[1] ^= 1 << 31
@@ -241,7 +271,7 @@ func (g *Graphics) DrawTriangles(dstID graphicsdriver.ImageID, srcIDs [graphics.
 		g.uniformVars[idx].value[13] ^= 1 << 31
 	}
 
-	var imgs [graphics.ShaderImageCount]textureVariable
+	var imgs [graphics.ShaderSrcImageCount]textureVariable
 	for i, srcID := range srcIDs {
 		if srcID == graphicsdriver.InvalidImageID {
 			continue
@@ -260,8 +290,13 @@ func (g *Graphics) DrawTriangles(dstID graphicsdriver.ImageID, srcIDs [graphics.
 	g.uniformVars = g.uniformVars[:0]
 
 	if fillRule != graphicsdriver.FillAll {
-		if err := destination.ensureStencilBuffer(); err != nil {
+		for _, dst := range destinations {
-			return err
+			if dst == nil {
+				continue
+			}
+			if err := dst.ensureStencilBuffer(); err != nil {
+				return err
+			}
 		}
 		g.context.ctx.Enable(gl.STENCIL_TEST)
 	}
@@ -273,6 +308,7 @@ func (g *Graphics) DrawTriangles(dstID graphicsdriver.ImageID, srcIDs [graphics.
 			int32(dstRegion.Region.Dx()),
 			int32(dstRegion.Region.Dy()),
 		)
+
 		switch fillRule {
 		case graphicsdriver.NonZero:
 			g.context.ctx.Clear(gl.STENCIL_BUFFER_BIT)
@@ -280,6 +316,7 @@ func (g *Graphics) DrawTriangles(dstID graphicsdriver.ImageID, srcIDs [graphics.
 			g.context.ctx.StencilOpSeparate(gl.FRONT, gl.KEEP, gl.KEEP, gl.INCR_WRAP)
 			g.context.ctx.StencilOpSeparate(gl.BACK, gl.KEEP, gl.KEEP, gl.DECR_WRAP)
 			g.context.ctx.ColorMask(false, false, false, false)
+
 			g.context.ctx.DrawElements(gl.TRIANGLES, int32(dstRegion.IndexCount), gl.UNSIGNED_INT, indexOffset*int(unsafe.Sizeof(uint32(0))))
 		case graphicsdriver.EvenOdd:
 			g.context.ctx.Clear(gl.STENCIL_BUFFER_BIT)

internal/graphicsdriver/opengl/program.go

@@ -258,8 +258,20 @@ func (g *Graphics) textureVariableName(idx int) string {
 	return name
 }
 
+func (g *Graphics) colorBufferVariableName(idx int) string {
+	if v, ok := g.colorBufferVariableNameCache[idx]; ok {
+		return v
+	}
+	if g.colorBufferVariableNameCache == nil {
+		g.colorBufferVariableNameCache = map[int]string{}
+	}
+	name := fmt.Sprintf("gl_FragData[%d]", idx)
+	g.colorBufferVariableNameCache[idx] = name
+	return name
+}
+
 // useProgram uses the program (programTexture).
-func (g *Graphics) useProgram(program program, uniforms []uniformVariable, textures [graphics.ShaderImageCount]textureVariable) error {
+func (g *Graphics) useProgram(program program, uniforms []uniformVariable, textures [graphics.ShaderSrcImageCount]textureVariable) error {
 	if g.state.lastProgram != program {
 		g.context.ctx.UseProgram(uint32(program))
 

internal/mipmap/mipmap.go

@@ -65,7 +65,7 @@ func (m *Mipmap) ReadPixels(graphicsDriver graphicsdriver.Graphics, pixels []byt
 	return m.orig.ReadPixels(graphicsDriver, pixels, region)
 }
 
-func (m *Mipmap) DrawTriangles(srcs [graphics.ShaderImageCount]*Mipmap, vertices []float32, indices []uint32, blend graphicsdriver.Blend, dstRegion image.Rectangle, srcRegions [graphics.ShaderImageCount]image.Rectangle, shader *atlas.Shader, uniforms []uint32, fillRule graphicsdriver.FillRule, canSkipMipmap bool) {
+func (m *Mipmap) DrawTriangles(srcs [graphics.ShaderSrcImageCount]*Mipmap, vertices []float32, indices []uint32, blend graphicsdriver.Blend, dstRegion image.Rectangle, srcRegions [graphics.ShaderSrcImageCount]image.Rectangle, shader *atlas.Shader, uniforms []uint32, fillRule graphicsdriver.FillRule, canSkipMipmap bool) {
 	if len(indices) == 0 {
 		return
 	}
@@ -103,7 +103,7 @@ func (m *Mipmap) DrawTriangles(srcs [graphics.ShaderImageCount]*Mipmap, vertices
 		}
 	}
 
-	var imgs [graphics.ShaderImageCount]*buffered.Image
+	var imgs [graphics.ShaderSrcImageCount]*buffered.Image
 	for i, src := range srcs {
 		if src == nil {
 			continue
@@ -127,6 +127,78 @@ func (m *Mipmap) DrawTriangles(srcs [graphics.ShaderImageCount]*Mipmap, vertices
 	m.deallocateMipmaps()
 }
 
+func DrawTrianglesMRT(dsts [graphics.ShaderDstImageCount]*Mipmap, srcs [graphics.ShaderSrcImageCount]*Mipmap, vertices []float32, indices []uint32, blend graphicsdriver.Blend, dstRegion image.Rectangle, srcRegions [graphics.ShaderSrcImageCount]image.Rectangle, shader *atlas.Shader, uniforms []uint32, fillRule graphicsdriver.FillRule, canSkipMipmap bool) {
+	if len(indices) == 0 {
+		return
+	}
+
+	level := 0
+	// TODO: Do we need to check all the sources' states of being volatile?
+	if !canSkipMipmap && srcs[0] != nil && canUseMipmap(srcs[0].imageType) {
+		level = math.MaxInt32
+		for i := 0; i < len(indices)/3; i++ {
+			const n = graphics.VertexFloatCount
+			dx0 := vertices[n*indices[3*i]+0]
+			dy0 := vertices[n*indices[3*i]+1]
+			sx0 := vertices[n*indices[3*i]+2]
+			sy0 := vertices[n*indices[3*i]+3]
+			dx1 := vertices[n*indices[3*i+1]+0]
+			dy1 := vertices[n*indices[3*i+1]+1]
+			sx1 := vertices[n*indices[3*i+1]+2]
+			sy1 := vertices[n*indices[3*i+1]+3]
+			dx2 := vertices[n*indices[3*i+2]+0]
+			dy2 := vertices[n*indices[3*i+2]+1]
+			sx2 := vertices[n*indices[3*i+2]+2]
+			sy2 := vertices[n*indices[3*i+2]+3]
+			if l := mipmapLevelFromDistance(dx0, dy0, dx1, dy1, sx0, sy0, sx1, sy1); level > l {
+				level = l
+			}
+			if l := mipmapLevelFromDistance(dx1, dy1, dx2, dy2, sx1, sy1, sx2, sy2); level > l {
+				level = l
+			}
+			if l := mipmapLevelFromDistance(dx2, dy2, dx0, dy0, sx2, sy2, sx0, sy0); level > l {
+				level = l
+			}
+		}
+		if level == math.MaxInt32 {
+			panic("mipmap: level must be calculated at least once but not")
+		}
+	}
+
+	var dstImgs [graphics.ShaderDstImageCount]*buffered.Image
+	for i, dst := range dsts {
+		if dst == nil {
+			continue
+		}
+		dstImgs[i] = dst.orig
+	}
+
+	var srcImgs [graphics.ShaderSrcImageCount]*buffered.Image
+	for i, src := range srcs {
+		if src == nil {
+			continue
+		}
+		if level != 0 {
+			if img := src.level(level); img != nil {
+				const n = graphics.VertexFloatCount
+				s := float32(pow2(level))
+				for i := 0; i < len(vertices)/n; i++ {
+					vertices[i*n+2] /= s
+					vertices[i*n+3] /= s
+				}
+				srcImgs[i] = img
+				continue
+			}
+		}
+		srcImgs[i] = src.orig
+	}
+
+	buffered.DrawTrianglesMRT(dstImgs, srcImgs, vertices, indices, blend, dstRegion, srcRegions, shader, uniforms, fillRule)
+	for _, dst := range dsts {
+		dst.deallocateMipmaps()
+	}
+}
+
 func (m *Mipmap) setImg(level int, img *buffered.Image) {
 	if m.imgs == nil {
 		m.imgs = map[int]*buffered.Image{}
@@ -187,7 +259,7 @@ func (m *Mipmap) level(level int) *buffered.Image {
 	s := buffered.NewImage(w2, h2, m.imageType)
 
 	dstRegion := image.Rect(0, 0, w2, h2)
-	s.DrawTriangles([graphics.ShaderImageCount]*buffered.Image{src}, vs, is, graphicsdriver.BlendCopy, dstRegion, [graphics.ShaderImageCount]image.Rectangle{}, shader, nil, graphicsdriver.FillAll)
+	s.DrawTriangles([graphics.ShaderSrcImageCount]*buffered.Image{src}, vs, is, graphicsdriver.BlendCopy, dstRegion, [graphics.ShaderSrcImageCount]image.Rectangle{}, shader, nil, graphicsdriver.FillAll)
 	m.setImg(level, s)
 
 	return m.imgs[level]

internal/shader/shader.go

@@ -215,6 +215,7 @@ func Compile(src []byte, vertexEntry, fragmentEntry string, textureCount int) (*
 	// TODO: Make a call graph and reorder the elements.
 
 	s.ir.TextureCount = textureCount
+
 	return &s.ir, nil
 }
 
@@ -741,8 +742,9 @@ func (cs *compileState) parseFuncParams(block *block, fname string, d *ast.FuncD
 	}
 
 	// If there is only one returning value, it is treated as a returning value.
+	// Only if not the fragment entrypoint.
 	// An array cannot be a returning value, especially for HLSL (#2923).
-	if len(out) == 1 && out[0].name == "" && out[0].typ.Main != shaderir.Array {
+	if fname != cs.fragmentEntry && len(out) == 1 && out[0].name == "" && out[0].typ.Main != shaderir.Array {
 		ret = out[0].typ
 		out = nil
 	}
@@ -820,10 +822,13 @@ func (cs *compileState) parseFunc(block *block, d *ast.FuncDecl) (function, bool
 				return function{}, false
 			}
 
-			if len(outParams) != 0 || returnType.Main != shaderir.Vec4 {
+			// The first out-param is treated as gl_FragColor in GLSL.
-				cs.addError(d.Pos(), "fragment entry point must have one returning vec4 value for a color")
+			if outParams[0].typ.Main != shaderir.Vec4 {
+				cs.addError(d.Pos(), "fragment entry point must have at least one returning vec4 value for a color")
 				return function{}, false
 			}
+			// Adjust the number of textures to write to
+			cs.ir.ColorsOutCount = len(outParams)
 
 			if cs.varyingParsed {
 				checkVaryings(inParams[1:])

internal/shaderir/glsl/glsl.go

@@ -87,8 +87,7 @@ precision highp int;
 #define mediump
 #define highp
 #endif
-
+`
-out vec4 fragColor;`
 	if version == GLSLVersionDefault {
 		prelude += "\n\n" + utilFunctions
 	}
@@ -420,7 +419,7 @@ func (c *compileContext) localVariableName(p *shaderir.Program, topBlock *shader
 		case idx < nv+1:
 			return fmt.Sprintf("V%d", idx-1)
 		default:
-			return fmt.Sprintf("l%d", idx-(nv+1))
+			return fmt.Sprintf("gl_FragData[%d]", idx-(nv+1))
 		}
 	default:
 		return fmt.Sprintf("l%d", idx)
@@ -595,7 +594,7 @@ func (c *compileContext) block(p *shaderir.Program, topBlock, block *shaderir.Bl
 		case shaderir.Return:
 			switch {
 			case topBlock == p.FragmentFunc.Block:
-				lines = append(lines, fmt.Sprintf("%sfragColor = %s;", idt, expr(&s.Exprs[0])))
+				lines = append(lines, fmt.Sprintf("%s%s;", idt, expr(&s.Exprs[0])))
 				// The 'return' statement is not required so far, as the fragment entrypoint has only one sentence so far. See adjustProgram implementation.
 			case len(s.Exprs) == 0:
 				lines = append(lines, idt+"return;")
@@ -645,15 +644,20 @@ func adjustProgram(p *shaderir.Program) *shaderir.Program {
 		Main: shaderir.Vec4, // gl_FragCoord
 	}
 	copy(inParams[1:], newP.Varyings)
+	// Out parameters of a fragment func are colors
+	outParams := make([]shaderir.Type, p.ColorsOutCount)
+	for i := range outParams {
+		outParams[i] = shaderir.Type{
+			Main: shaderir.Vec4,
+		}
+	}
+	newP.FragmentFunc.Block.LocalVarIndexOffset += (p.ColorsOutCount-1)
 
 	newP.Funcs = append(newP.Funcs, shaderir.Func{
 		Index:     funcIdx,
 		InParams:  inParams,
-		OutParams: nil,
+		OutParams: outParams,
-		Return: shaderir.Type{
+		Block:     newP.FragmentFunc.Block,
-			Main: shaderir.Vec4,
-		},
-		Block: newP.FragmentFunc.Block,
 	})
 
 	// Create an AST to call the new function.
@@ -663,7 +667,7 @@ func adjustProgram(p *shaderir.Program) *shaderir.Program {
 			Index: funcIdx,
 		},
 	}
-	for i := 0; i < 1+len(newP.Varyings); i++ {
+	for i := 0; i < 1+len(newP.Varyings)+p.ColorsOutCount; i++ {
 		call = append(call, shaderir.Expr{
 			Type:  shaderir.LocalVariable,
 			Index: i,

internal/shaderir/program.go

@@ -30,15 +30,16 @@ const (
 )
 
 type Program struct {
-	UniformNames []string
+	UniformNames   []string
-	Uniforms     []Type
+	Uniforms       []Type
-	TextureCount int
+	TextureCount   int
-	Attributes   []Type
+	ColorsOutCount int
-	Varyings     []Type
+	Attributes     []Type
-	Funcs        []Func
+	Varyings       []Type
-	VertexFunc   VertexFunc
+	Funcs          []Func
-	FragmentFunc FragmentFunc
+	VertexFunc     VertexFunc
-	Unit         Unit
+	FragmentFunc   FragmentFunc
+	Unit           Unit
 
 	uniformFactors []uint32
 }

internal/ui/image.go

@@ -77,7 +77,7 @@ func (i *Image) Deallocate() {
 	i.mipmap.Deallocate()
 }
 
-func (i *Image) DrawTriangles(srcs [graphics.ShaderImageCount]*Image, vertices []float32, indices []uint32, blend graphicsdriver.Blend, dstRegion image.Rectangle, srcRegions [graphics.ShaderImageCount]image.Rectangle, shader *Shader, uniforms []uint32, fillRule graphicsdriver.FillRule, canSkipMipmap bool, antialias bool) {
+func (i *Image) DrawTriangles(srcs [graphics.ShaderSrcImageCount]*Image, vertices []float32, indices []uint32, blend graphicsdriver.Blend, dstRegion image.Rectangle, srcRegions [graphics.ShaderSrcImageCount]image.Rectangle, shader *Shader, uniforms []uint32, fillRule graphicsdriver.FillRule, canSkipMipmap bool, antialias bool) {
 	if i.modifyCallback != nil {
 		i.modifyCallback()
 	}
@@ -104,7 +104,7 @@ func (i *Image) DrawTriangles(srcs [graphics.ShaderImageCount]*Image, vertices [
 
 	i.flushBufferIfNeeded()
 
-	var srcMipmaps [graphics.ShaderImageCount]*mipmap.Mipmap
+	var srcMipmaps [graphics.ShaderSrcImageCount]*mipmap.Mipmap
 	for i, src := range srcs {
 		if src == nil {
 			continue
@@ -116,6 +116,30 @@ func (i *Image) DrawTriangles(srcs [graphics.ShaderImageCount]*Image, vertices [
 	i.mipmap.DrawTriangles(srcMipmaps, vertices, indices, blend, dstRegion, srcRegions, shader.shader, uniforms, fillRule, canSkipMipmap)
 }
 
+func DrawTrianglesMRT(dsts [graphics.ShaderDstImageCount]*Image, srcs [graphics.ShaderSrcImageCount]*Image, vertices []float32, indices []uint32, blend graphicsdriver.Blend, dstRegion image.Rectangle, srcRegions [graphics.ShaderSrcImageCount]image.Rectangle, shader *Shader, uniforms []uint32, fillRule graphicsdriver.FillRule, canSkipMipmap bool, antialias bool) {
+	var dstMipmaps [graphics.ShaderDstImageCount]*mipmap.Mipmap
+	for i, dst := range dsts {
+		if dst.modifyCallback != nil {
+			dst.modifyCallback()
+		}
+
+		dst.lastBlend = blend
+		dst.flushBufferIfNeeded()
+		dstMipmaps[i] = dst.mipmap
+	}
+
+	var srcMipmaps [graphics.ShaderSrcImageCount]*mipmap.Mipmap
+	for i, src := range srcs {
+		if src == nil {
+			continue
+		}
+		src.flushBufferIfNeeded()
+		srcMipmaps[i] = src.mipmap
+	}
+
+	mipmap.DrawTrianglesMRT(dstMipmaps, srcMipmaps, vertices, indices, blend, dstRegion, srcRegions, shader.shader, uniforms, fillRule, canSkipMipmap)
+}
+
 func (i *Image) WritePixels(pix []byte, region image.Rectangle) {
 	if i.modifyCallback != nil {
 		i.modifyCallback()
@@ -175,7 +199,7 @@ func (i *Image) Fill(r, g, b, a float32, region image.Rectangle) {
 		r, g, b, a)
 	is := graphics.QuadIndices()
 
-	srcs := [graphics.ShaderImageCount]*Image{i.ui.whiteImage}
+	srcs := [graphics.ShaderSrcImageCount]*Image{i.ui.whiteImage}
 
 	blend := graphicsdriver.BlendCopy
 	// If possible, use BlendSourceOver to encourage batching (#2817).
@@ -183,7 +207,7 @@ func (i *Image) Fill(r, g, b, a float32, region image.Rectangle) {
 		blend = graphicsdriver.BlendSourceOver
 	}
 	// i.lastBlend is updated in DrawTriangles.
-	i.DrawTriangles(srcs, i.tmpVerticesForFill, is, blend, region, [graphics.ShaderImageCount]image.Rectangle{}, NearestFilterShader, nil, graphicsdriver.FillAll, true, false)
+	i.DrawTriangles(srcs, i.tmpVerticesForFill, is, blend, region, [graphics.ShaderSrcImageCount]image.Rectangle{}, NearestFilterShader, nil, graphicsdriver.FillAll, true, false)
 }
 
 type bigOffscreenImage struct {
@@ -217,7 +241,7 @@ func (i *bigOffscreenImage) deallocate() {
 	i.dirty = false
 }
 
-func (i *bigOffscreenImage) drawTriangles(srcs [graphics.ShaderImageCount]*Image, vertices []float32, indices []uint32, blend graphicsdriver.Blend, dstRegion image.Rectangle, srcRegions [graphics.ShaderImageCount]image.Rectangle, shader *Shader, uniforms []uint32, fillRule graphicsdriver.FillRule, canSkipMipmap bool, antialias bool) {
+func (i *bigOffscreenImage) drawTriangles(srcs [graphics.ShaderSrcImageCount]*Image, vertices []float32, indices []uint32, blend graphicsdriver.Blend, dstRegion image.Rectangle, srcRegions [graphics.ShaderSrcImageCount]image.Rectangle, shader *Shader, uniforms []uint32, fillRule graphicsdriver.FillRule, canSkipMipmap bool, antialias bool) {
 	if i.blend != blend {
 		i.flush()
 	}
@@ -240,7 +264,7 @@ func (i *bigOffscreenImage) drawTriangles(srcs [graphics.ShaderImageCount]*Image
 
 	// Copy the current rendering result to get the correct blending result.
 	if blend != graphicsdriver.BlendSourceOver && !i.dirty {
-		srcs := [graphics.ShaderImageCount]*Image{i.orig}
+		srcs := [graphics.ShaderSrcImageCount]*Image{i.orig}
 		if len(i.tmpVerticesForCopying) < 4*graphics.VertexFloatCount {
 			i.tmpVerticesForCopying = make([]float32, 4*graphics.VertexFloatCount)
 		}
@@ -252,7 +276,7 @@ func (i *bigOffscreenImage) drawTriangles(srcs [graphics.ShaderImageCount]*Image
 			1, 1, 1, 1)
 		is := graphics.QuadIndices()
 		dstRegion := image.Rect(0, 0, i.region.Dx()*bigOffscreenScale, i.region.Dy()*bigOffscreenScale)
-		i.image.DrawTriangles(srcs, i.tmpVerticesForCopying, is, graphicsdriver.BlendCopy, dstRegion, [graphics.ShaderImageCount]image.Rectangle{}, NearestFilterShader, nil, graphicsdriver.FillAll, true, false)
+		i.image.DrawTriangles(srcs, i.tmpVerticesForCopying, is, graphicsdriver.BlendCopy, dstRegion, [graphics.ShaderSrcImageCount]image.Rectangle{}, NearestFilterShader, nil, graphicsdriver.FillAll, true, false)
 	}
 
 	for idx := 0; idx < len(vertices); idx += graphics.VertexFloatCount {
@@ -284,7 +308,7 @@ func (i *bigOffscreenImage) flush() {
 	// Mark the offscreen clean earlier to avoid recursive calls.
 	i.dirty = false
 
-	srcs := [graphics.ShaderImageCount]*Image{i.image}
+	srcs := [graphics.ShaderSrcImageCount]*Image{i.image}
 	if len(i.tmpVerticesForFlushing) < 4*graphics.VertexFloatCount {
 		i.tmpVerticesForFlushing = make([]float32, 4*graphics.VertexFloatCount)
 	}
@@ -300,7 +324,7 @@ func (i *bigOffscreenImage) flush() {
 	if i.blend != graphicsdriver.BlendSourceOver {
 		blend = graphicsdriver.BlendCopy
 	}
-	i.orig.DrawTriangles(srcs, i.tmpVerticesForFlushing, is, blend, dstRegion, [graphics.ShaderImageCount]image.Rectangle{}, LinearFilterShader, nil, graphicsdriver.FillAll, true, false)
+	i.orig.DrawTriangles(srcs, i.tmpVerticesForFlushing, is, blend, dstRegion, [graphics.ShaderSrcImageCount]image.Rectangle{}, LinearFilterShader, nil, graphicsdriver.FillAll, true, false)
 
 	i.image.clear()
 	i.dirty = false