mipmap: Stop using negative mipmaps

Negative mipmaps tend to allocate extremely big images.

Instead, encourage to use images with explicit padding when enlarging
the image.

Fixes #1400

ebitenutil/shapes.go

@@ -15,6 +15,7 @@
 package ebitenutil
 
 import (
+	"image"
 	"image/color"
 	"math"
 
@@ -23,7 +24,7 @@ import (
 )
 
 var (
-	emptyImage = ebiten.NewImage(1, 1)
+	emptyImage = ebiten.NewImage(3, 3)
 )
 
 func init() {
@@ -36,17 +37,16 @@ func init() {
 //
 // DrawLine is not concurrent-safe.
 func DrawLine(dst *ebiten.Image, x1, y1, x2, y2 float64, clr color.Color) {
-	ew, eh := emptyImage.Size()
 	length := math.Hypot(x2-x1, y2-y1)
 
 	op := &ebiten.DrawImageOptions{}
-	op.GeoM.Scale(length/float64(ew), 1/float64(eh))
+	op.GeoM.Scale(length, 1)
 	op.GeoM.Rotate(math.Atan2(y2-y1, x2-x1))
 	op.GeoM.Translate(x1, y1)
 	op.ColorM = colormcache.ColorToColorM(clr)
 	// Filter must be 'nearest' filter (default).
 	// Linear filtering would make edges blurred.
-	dst.DrawImage(emptyImage, op)
+	dst.DrawImage(emptyImage.SubImage(image.Rect(1, 1, 2, 2)).(*ebiten.Image), op)
 }
 
 // DrawRect draws a rectangle on the given destination dst.
@@ -55,13 +55,11 @@ func DrawLine(dst *ebiten.Image, x1, y1, x2, y2 float64, clr color.Color) {
 //
 // DrawRect is not concurrent-safe.
 func DrawRect(dst *ebiten.Image, x, y, width, height float64, clr color.Color) {
-	ew, eh := emptyImage.Size()
-
 	op := &ebiten.DrawImageOptions{}
-	op.GeoM.Scale(width/float64(ew), height/float64(eh))
+	op.GeoM.Scale(width, height)
 	op.GeoM.Translate(x, y)
 	op.ColorM = colormcache.ColorToColorM(clr)
 	// Filter must be 'nearest' filter (default).
 	// Linear filtering would make edges blurred.
-	dst.DrawImage(emptyImage, op)
+	dst.DrawImage(emptyImage.SubImage(image.Rect(1, 1, 2, 2)).(*ebiten.Image), op)
 }

examples/polygons/main.go

@@ -18,6 +18,7 @@ package main
 
 import (
 	"fmt"
+	"image"
 	"image/color"
 	"log"
 	"math"
@@ -33,7 +34,7 @@ const (
 )
 
 var (
-	emptyImage = ebiten.NewImage(16, 16)
+	emptyImage = ebiten.NewImage(3, 3)
 )
 
 func init() {
@@ -126,7 +127,7 @@ func (g *Game) Draw(screen *ebiten.Image) {
 	for i := 0; i < g.ngon; i++ {
 		indices = append(indices, uint16(i), uint16(i+1)%uint16(g.ngon), uint16(g.ngon))
 	}
-	screen.DrawTriangles(g.vertices, indices, emptyImage, op)
+	screen.DrawTriangles(g.vertices, indices, emptyImage.SubImage(image.Rect(1, 1, 2, 2)).(*ebiten.Image), op)
 
 	msg := fmt.Sprintf("TPS: %0.2f\n%d-gon\nPress <- or -> to change the number of the vertices", ebiten.CurrentTPS(), g.ngon)
 	ebitenutil.DebugPrint(screen, msg)

examples/shapes/main.go

@@ -18,6 +18,7 @@ package main
 
 import (
 	"fmt"
+	"image"
 	"image/color"
 	"log"
 	"math"
@@ -32,7 +33,7 @@ const (
 )
 
 var (
-	emptyImage = ebiten.NewImage(16, 16)
+	emptyImage = ebiten.NewImage(3, 3)
 )
 
 func init() {
@@ -161,18 +162,20 @@ func (g *Game) Update() error {
 }
 
 func (g *Game) Draw(screen *ebiten.Image) {
+	src := emptyImage.SubImage(image.Rect(1, 1, 2, 2)).(*ebiten.Image)
+
 	cf := float64(g.count)
 	v, i := line(100, 100, 300, 100, color.RGBA{0xff, 0xff, 0xff, 0xff})
-	screen.DrawTriangles(v, i, emptyImage, nil)
+	screen.DrawTriangles(v, i, src, nil)
 	v, i = line(50, 150, 50, 350, color.RGBA{0xff, 0xff, 0x00, 0xff})
-	screen.DrawTriangles(v, i, emptyImage, nil)
+	screen.DrawTriangles(v, i, src, nil)
 	v, i = line(50, 100+float32(cf), 200+float32(cf), 250, color.RGBA{0x00, 0xff, 0xff, 0xff})
-	screen.DrawTriangles(v, i, emptyImage, nil)
+	screen.DrawTriangles(v, i, src, nil)
 
 	v, i = rect(50+float32(cf), 50+float32(cf), 100+float32(cf), 100+float32(cf), color.RGBA{0x80, 0x80, 0x80, 0x80})
-	screen.DrawTriangles(v, i, emptyImage, nil)
+	screen.DrawTriangles(v, i, src, nil)
 	v, i = rect(300-float32(cf), 50, 120, 120, color.RGBA{0x00, 0x80, 0x00, 0x80})
-	screen.DrawTriangles(v, i, emptyImage, nil)
+	screen.DrawTriangles(v, i, src, nil)
 
 	ebitenutil.DebugPrint(screen, fmt.Sprintf("TPS: %0.2f", ebiten.CurrentTPS()))
 }

image_test.go

@@ -798,10 +798,10 @@ func TestImageStretch(t *testing.T) {
 	dst := NewImage(w, 4096)
 loop:
 	for h := 1; h <= 32; h++ {
-		src := NewImage(w, h)
+		src := NewImage(w+2, h+2)
 
-		pix := make([]byte, 4*w*h)
+		pix := make([]byte, 4*(w+2)*(h+2))
-		for i := 0; i < w*h; i++ {
+		for i := 0; i < (w+2)*(h+2); i++ {
 			pix[4*i] = 0xff
 			pix[4*i+3] = 0xff
 		}
@@ -812,7 +812,7 @@ loop:
 			dst.Clear()
 			op := &DrawImageOptions{}
 			op.GeoM.Scale(1, float64(i)/float64(h))
-			dst.DrawImage(src, op)
+			dst.DrawImage(src.SubImage(image.Rect(1, 1, w+1, h+1)).(*Image), op)
 			for j := -1; j <= 1; j++ {
 				if i+j < 0 {
 					continue

internal/mipmap/mipmap.go

@@ -205,20 +205,6 @@ func (m *Mipmap) level(level int) *buffered.Image {
 		h := sizeForLevel(m.height, level-1)
 		vs = graphics.QuadVertices(0, 0, float32(w), float32(h), 0.5, 0, 0, 0.5, 0, 0, 1, 1, 1, 1, false)
 		filter = driver.FilterLinear
-	case level == -1:
-		src = m.orig
-		vs = graphics.QuadVertices(0, 0, float32(m.width), float32(m.height), 2, 0, 0, 2, 0, 0, 1, 1, 1, 1, false)
-		filter = driver.FilterNearest
-	case level < -1:
-		src = m.level(level + 1)
-		if src == nil {
-			m.imgs[level] = nil
-			return nil
-		}
-		w := sizeForLevel(m.width, level-1)
-		h := sizeForLevel(m.height, level-1)
-		vs = graphics.QuadVertices(0, 0, float32(w), float32(h), 2, 0, 0, 2, 0, 0, 1, 1, 1, 1, false)
-		filter = driver.FilterNearest
 	default:
 		panic(fmt.Sprintf("ebiten: invalid level: %d", level))
 	}
@@ -246,16 +232,10 @@ func (m *Mipmap) level(level int) *buffered.Image {
 }
 
 func sizeForLevel(x int, level int) int {
-	if level > 0 {
+	for i := 0; i < level; i++ {
-		for i := 0; i < level; i++ {
+		x /= 2
-			x /= 2
+		if x == 0 {
-			if x == 0 {
+			return 0
-				return 0
-			}
-		}
-	} else {
-		for i := 0; i < -level; i++ {
-			x *= 2
 		}
 	}
 	return x
@@ -295,9 +275,6 @@ func mipmapLevelFromDistance(dx0, dy0, dx1, dy1, sx0, sy0, sx1, sy1 float32, fil
 
 	// Scale can be infinite when the specified scale is extremely big (#1398).
 	if math.IsInf(float64(scale), 0) {
-		if filter == driver.FilterNearest {
-			return -maxLevel
-		}
 		return 0
 	}
 
@@ -306,42 +283,6 @@ func mipmapLevelFromDistance(dx0, dy0, dx1, dy1, sx0, sy0, sx1, sy1 float32, fil
 		return 0
 	}
 
-	// Use 'negative' mipmap to render edges correctly (#611, #907).
-	// It looks like 128 is the enlargement factor that causes edge missings to pass the test TestImageStretch,
-	// but we use 32 here for environments where the float precision is low (#1044, #1270).
-	var tooBigScale float32 = 32
-
-	if scale >= tooBigScale*tooBigScale {
-		// If the filter is not nearest, the target needs to be rendered with graduation. Don't use mipmaps.
-		if filter != driver.FilterNearest {
-			return 0
-		}
-
-		const mipmapMaxSize = 1024
-		w, h := sx1-sx0, sy1-sy0
-		if w >= mipmapMaxSize || h >= mipmapMaxSize {
-			return 0
-		}
-
-		level := 0
-		for scale >= tooBigScale*tooBigScale {
-			level--
-			scale /= 4
-			w *= 2
-			h *= 2
-			if w >= mipmapMaxSize || h >= mipmapMaxSize {
-				break
-			}
-		}
-
-		// If tooBigScale is 32, level -6 means that the maximum scale is 32 * 2^6 = 2048. This should be
-		// enough.
-		if level < -maxLevel {
-			level = -maxLevel
-		}
-		return level
-	}
-
 	if filter != driver.FilterLinear {
 		return 0
 	}
@@ -378,16 +319,8 @@ func mipmapLevelFromDistance(dx0, dy0, dx1, dy1, sx0, sy0, sx1, sy1 float32, fil
 }
 
 func pow2(power int) float32 {
-	if power >= 0 {
+	x := 1
-		x := 1
+	return float32(x << uint(power))
-		return float32(x << uint(power))
-	}
-
-	x := float32(1)
-	for i := 0; i < -power; i++ {
-		x /= 2
-	}
-	return x
 }
 
 type Shader struct {

internal/restorable/image.go

@@ -113,6 +113,7 @@ var emptyImage *Image
 func init() {
 	// Use a big-enough image as an rendering source. By enlarging with x128, this can reach to 16384.
 	// See #907 for details.
+	// TODO: This doesn't have to be 128 due to the 1px padding. 3x3 should be enough.
 	const w, h = 128, 128
 	emptyImage = &Image{
 		image:    graphicscommand.NewImage(w, h),

vector/path.go

@@ -18,6 +18,7 @@
 package vector
 
 import (
+	"image"
 	"image/color"
 	"math"
 
@@ -25,7 +26,7 @@ import (
 	"github.com/hajimehoshi/ebiten/v2/vector/internal/triangulate"
 )
 
-var emptyImage = ebiten.NewImage(1, 1)
+var emptyImage = ebiten.NewImage(3, 3)
 
 func init() {
 	emptyImage.Fill(color.White)
@@ -138,5 +139,5 @@ func (p *Path) Fill(dst *ebiten.Image, op *FillOptions) {
 		}
 		base += uint16(len(seg))
 	}
-	dst.DrawTriangles(vertices, indices, emptyImage, nil)
+	dst.DrawTriangles(vertices, indices, emptyImage.SubImage(image.Rect(1, 1, 2, 2)).(*ebiten.Image), nil)
 }