graphicscommand: Span to 1/3 pixels

The center of pixels is problematic as the behavior depends on GPU.
In order to avoid this, align the vertices with about 1/3 pixels.

Updates #929
Fixes #1171

image_test.go

@@ -16,6 +16,7 @@ package ebiten_test
 
 import (
 	"bytes"
+	"fmt"
 	"image"
 	"image/color"
 	"image/draw"
@@ -2067,10 +2068,37 @@ func BenchmarkImageDrawOver(b *testing.B) {
 }
 
 // Issue #1171
-func Disabled_TestImageFloatTranslate(t *testing.T) {
+func TestImageFloatTranslate(t *testing.T) {
-	const w, h = 16, 16
+	const w, h = 32, 32
 
-	dst, _ := NewImage(320, 240, FilterDefault)
+	for s := 2; s <= 8; s++ {
+		s := s
+		t.Run(fmt.Sprintf("scale%d", s), func(t *testing.T) {
+			check := func(src *Image) {
+				dst, _ := NewImage(w*(s+1), h*(s+1), FilterDefault)
+				dst.Fill(color.RGBA{0xff, 0, 0, 0xff})
+
+				op := &DrawImageOptions{}
+				op.GeoM.Scale(float64(s), float64(s))
+				op.GeoM.Translate(0, 0.501)
+				dst.DrawImage(src, op)
+
+				for j := 0; j < h*s+1; j++ {
+					for i := 0; i < w*s; i++ {
+						got := dst.At(i, j)
+						x := byte(0xff)
+						if j > 0 {
+							x = (byte(j) - 1) / byte(s)
+						}
+						want := color.RGBA{x, 0, 0, 0xff}
+						if got != want {
+							t.Errorf("At(%d, %d): got: %v, want: %v", i, j, got, want)
+						}
+					}
+				}
+			}
+
+			t.Run("image", func(t *testing.T) {
 				src, _ := NewImage(w, h, FilterDefault)
 				pix := make([]byte, 4*w*h)
 				for j := 0; j < h; j++ {
@@ -2080,50 +2108,21 @@ func Disabled_TestImageFloatTranslate(t *testing.T) {
 					}
 				}
 				src.ReplacePixels(pix)
+				check(src)
+			})
 
-	op := &DrawImageOptions{}
+			t.Run("subimage", func(t *testing.T) {
-	op.GeoM.Scale(2, 2)
+				src, _ := NewImage(w*s, h*s, FilterDefault)
-	op.GeoM.Translate(0, 0.501)
+				pix := make([]byte, 4*(w*s)*(h*s))
-	dst.DrawImage(src, op)
+				for j := 0; j < h*s; j++ {
-
+					for i := 0; i < w*s; i++ {
-	for j := 1; j < h*2+1; j++ {
+						pix[4*(j*(w*s)+i)] = byte(j)
-		for i := 0; i < w*2; i++ {
+						pix[4*(j*(w*s)+i)+3] = 0xff
-			got := dst.At(i, j)
-			want := color.RGBA{(byte(j) - 1) / 2, 0, 0, 0xff}
-			if got != want {
-				t.Errorf("At(%d, %d): got: %v, want: %v", i, j, got, want)
-			}
-		}
-	}
-}
-
-// Issue #1171
-func Disabled_TestImageSubImageFloatTranslate(t *testing.T) {
-	const w, h = 16, 16
-
-	dst, _ := NewImage(320, 240, FilterDefault)
-	src, _ := NewImage(w*2, h*2, FilterDefault)
-	pix := make([]byte, 4*(w*2)*(h*2))
-	for j := 0; j < h*2; j++ {
-		for i := 0; i < w*2; i++ {
-			pix[4*(j*(w*2)+i)] = byte(j)
-			pix[4*(j*(w*2)+i)+3] = 0xff
 					}
 				}
 				src.ReplacePixels(pix)
-
+				check(src.SubImage(image.Rect(0, 0, w, h)).(*Image))
-	op := &DrawImageOptions{}
+			})
-	op.GeoM.Scale(2, 2)
+		})
-	op.GeoM.Translate(0, 0.501)
-	dst.DrawImage(src.SubImage(image.Rect(0, 0, w, h)).(*Image), op)
-
-	for j := 1; j < h*2+1; j++ {
-		for i := 0; i < w*2; i++ {
-			got := dst.At(i, j)
-			want := color.RGBA{(byte(j) - 1) / 2, 0, 0, 0xff}
-			if got != want {
-				t.Errorf("At(%d, %d): got: %v, want: %v", i, j, got, want)
-			}
-		}
 	}
 }

internal/graphicscommand/command.go

@@ -203,14 +203,6 @@ func (q *commandQueue) Enqueue(command command) {
 	q.commands = append(q.commands, command)
 }
 
-func fract(x float32) float32 {
-	return x - float32(math.Floor(float64(x)))
-}
-
-const (
-	dstAdjustmentFactor = 1.0 / 256.0
-)
-
 // Flush flushes the command queue.
 func (q *commandQueue) Flush() error {
 	if len(q.commands) == 0 {
@@ -236,22 +228,22 @@ func (q *commandQueue) Flush() error {
 			vs[i*graphics.VertexFloatNum+6] /= s.width
 			vs[i*graphics.VertexFloatNum+7] /= s.height
 
-			// Adjust the destination position to avoid jaggy (#929).
+			// Avoid the center of the pixel, which is problematic (#929, #1171).
-			// This is not a perfect solution since texels on a texture can take a position on borders
+			// Instead, align the vertices with about 1/3 pixels.
-			// which can cause jaggy. But adjusting only edges should work in most cases.
+			for idx := 0; idx < 2; idx++ {
-			// The ideal solution is to fix shaders, but this makes the applications slow by adding 'if'
+				x := vs[i*graphics.VertexFloatNum+idx]
-			// branches.
+				int := float32(math.Floor(float64(x)))
-			switch f := fract(vs[i*graphics.VertexFloatNum+0]); {
+				frac := x - int
-			case 0.5-dstAdjustmentFactor <= f && f < 0.5:
+				switch {
-				vs[i*graphics.VertexFloatNum+0] -= f - (0.5 - dstAdjustmentFactor)
+				case frac < 3.0/16.0:
-			case 0.5 <= f && f < 0.5+dstAdjustmentFactor:
+					vs[i*graphics.VertexFloatNum+idx] = int
-				vs[i*graphics.VertexFloatNum+0] += (0.5 + dstAdjustmentFactor) - f
+				case frac < 8.0/16.0:
+					vs[i*graphics.VertexFloatNum+idx] = int + 5.0/16.0
+				case frac < 13.0/16.0:
+					vs[i*graphics.VertexFloatNum+idx] = int + 11.0/16.0
+				default:
+					vs[i*graphics.VertexFloatNum+idx] = int + 16.0/16.0
 				}
-			switch f := fract(vs[i*graphics.VertexFloatNum+1]); {
-			case 0.5-dstAdjustmentFactor <= f && f < 0.5:
-				vs[i*graphics.VertexFloatNum+1] -= f - (0.5 - dstAdjustmentFactor)
-			case 0.5 <= f && f < 0.5+dstAdjustmentFactor:
-				vs[i*graphics.VertexFloatNum+1] += (0.5 + dstAdjustmentFactor) - f
 			}
 		}
 	} else {