vector: bug fix: a callback for an image and its sub-image should be treated correctly

Closes #3355

Author: hajimehoshi

image.go

@@ -1605,6 +1605,14 @@ func (*Image) private() {
 
 var currentCallbackToken atomic.Int64
 
+//go:linkname originalImage
+func originalImage(img *Image) *Image {
+	if img.isSubImage() {
+		return img.original
+	}
+	return img
+}
+
 //go:linkname addUsageCallback
 func addUsageCallback(img *Image, callback func(image *Image)) int64 {
 	return img.addUsageCallback(img, callback)

vector/fill.go

@@ -16,6 +16,7 @@ package vector
 
 import (
 	"fmt"
+	"image"
 	"slices"
 
 	"github.com/hajimehoshi/ebiten/v2"
@@ -129,6 +130,7 @@ var theAtlas atlas
 type fillPathsState struct {
 	paths  []*Path
 	colors []ebiten.ColorScale
+	bounds []image.Rectangle
 
 	vertices []ebiten.Vertex
 	indices  []uint32
@@ -143,10 +145,11 @@ func (f *fillPathsState) reset() {
 		p.Reset()
 	}
 	f.paths = f.paths[:0]
+	f.bounds = f.bounds[:0]
 	f.colors = slices.Delete(f.colors, 0, len(f.colors))
 }
 
-func (f *fillPathsState) addPath(path *Path, clr ebiten.ColorScale) {
+func (f *fillPathsState) addPath(path *Path, bounds image.Rectangle, clr ebiten.ColorScale) {
 	if path == nil {
 		return
 	}
@@ -163,6 +166,7 @@ func (f *fillPathsState) addPath(path *Path, clr ebiten.ColorScale) {
 		dst.subPaths[i].ops = slices.Grow(dst.subPaths[i].ops, len(subPath.ops))[:len(subPath.ops)]
 		copy(dst.subPaths[i].ops, subPath.ops)
 	}
+	f.bounds = append(f.bounds, bounds)
 	f.colors = append(f.colors, clr)
 }
 
@@ -481,6 +485,10 @@ func (f *fillPathsState) fillPaths(dst *ebiten.Image) {
 				panic(fmt.Sprintf("vector: failed to create stencil buffer even-odd shader: %v", err))
 			}
 		}
-		dst.DrawTrianglesShader32(vs, is, shader, op)
+		dst2 := dst
+		if dst.Bounds() != f.bounds[i] {
+			dst2 = dst.SubImage(f.bounds[i]).(*ebiten.Image)
+		}
+		dst2.DrawTrianglesShader32(vs, is, shader, op)
 	}
 }

vector/util.go

@@ -353,6 +353,9 @@ func FillPath(dst *ebiten.Image, path *Path, fillOptions *FillOptions, drawPathO
 	defer theFillPathM.Unlock()
 
 	// Remove the previous registered callbacks.
+	bounds := dst.Bounds()
+	// Get the original image if dst is a sub-image to integrate the callbacks.
+	dst = originalImage(dst)
 	if token, ok := theCallbackTokens[dst]; ok {
 		removeUsageCallback(dst, token)
 	}
@@ -369,13 +372,17 @@ func FillPath(dst *ebiten.Image, path *Path, fillOptions *FillOptions, drawPathO
 	s.antialias = drawPathOptions.AntiAlias
 	s.blend = drawPathOptions.Blend
 	s.fillRule = fillOptions.FillRule
-	s.addPath(path, drawPathOptions.ColorScale)
+	s.addPath(path, bounds, drawPathOptions.ColorScale)
 
 	// Use an independent callback function to avoid unexpected captures.
 	theCallbackTokens[dst] = addUsageCallback(dst, fillPathCallback)
 }
 
 func fillPathCallback(dst *ebiten.Image) {
+	if originalImage(dst) != dst {
+		panic("vector: dst must be the original image")
+	}
+
 	theFillPathM.Lock()
 	defer theFillPathM.Unlock()
 
@@ -404,6 +411,9 @@ func StrokePath(dst *ebiten.Image, path *Path, strokeOptions *StrokeOptions, dra
 	FillPath(dst, &stroke, nil, drawPathOptions)
 }
 
+//go:linkname originalImage github.com/hajimehoshi/ebiten/v2.originalImage
+func originalImage(img *ebiten.Image) *ebiten.Image
+
 //go:linkname addUsageCallback github.com/hajimehoshi/ebiten/v2.addUsageCallback
 func addUsageCallback(img *ebiten.Image, fn func(img *ebiten.Image)) int64
 

vector/util_test.go

@@ -170,3 +170,29 @@ func TestRaceConditionWithSubImage(t *testing.T) {
 	}
 	wg.Wait()
 }
+
+// Issue #3355
+func TestFillPathSubImageAndImage(t *testing.T) {
+	dst := ebiten.NewImage(200, 200)
+	defer dst.Deallocate()
+	for i := range 100 {
+		var path vector.Path
+		path.LineTo(0, 0)
+		path.LineTo(0, 100)
+		path.LineTo(100, 100)
+		path.LineTo(100, 0)
+		path.LineTo(0, 0)
+		path.Close()
+		drawOp := &vector.DrawPathOptions{}
+		drawOp.ColorScale.ScaleWithColor(color.RGBA{255, 0, 0, 255})
+		subDst := dst.SubImage(image.Rect(0, 0, 100, 100)).(*ebiten.Image)
+		vector.FillPath(subDst, &path, nil, drawOp)
+		drawOp.ColorScale.Reset()
+		drawOp.ColorScale.ScaleWithColor(color.RGBA{0, 255, 0, 255})
+		vector.FillPath(dst, &path, nil, drawOp)
+
+		if got, want := dst.At(50, 50), (color.RGBA{0, 255, 0, 255}); got != want {
+			t.Errorf("%d: got: %v, want: %v", i, got, want)
+		}
+	}
+}