internal/atlas: bug fix: there should be multiple temporaryBytes objects for pipelining

Closes #2716

internal/atlas/image.go

@@ -39,7 +39,19 @@ type temporaryBytes struct {
 	notFullyUsedTime int
 }
 
-var theTemporaryBytes temporaryBytes
+var (
+	theTemporaryBytesSet [2]temporaryBytes
+	temporaryBytesIndex  int
+)
+
+func currentTemporaryBytes() *temporaryBytes {
+	return &theTemporaryBytesSet[temporaryBytesIndex]
+}
+
+func switchTemporaryBytes() {
+	temporaryBytesIndex++
+	temporaryBytesIndex %= len(theTemporaryBytesSet)
+}
 
 func temporaryBytesSize(size int) int {
 	l := 16
@@ -551,13 +563,13 @@ func (i *Image) writePixels(pix []byte, region image.Rectangle) {
 		}
 
 		// Copy pixels in the case when pix is modified before the graphics command is executed.
-		pix2 := theTemporaryBytes.alloc(len(pix))
+		pix2 := currentTemporaryBytes().alloc(len(pix))
 		copy(pix2, pix)
 		i.backend.restorable.WritePixels(pix2, region)
 		return
 	}
 
-	pixb := theTemporaryBytes.alloc(4 * r.Dx() * r.Dy())
+	pixb := currentTemporaryBytes().alloc(4 * r.Dx() * r.Dy())
 
 	// Clear the edges. pixb might not be zero-cleared.
 	// TODO: These loops assume that paddingSize is 1.
@@ -795,7 +807,8 @@ func EndFrame(graphicsDriver graphicsdriver.Graphics, swapBuffersForGL func()) e
 		return err
 	}
 
-	theTemporaryBytes.resetAtFrameEnd()
+	currentTemporaryBytes().resetAtFrameEnd()
+	switchTemporaryBytes()
 
 	for b := range theSourceBackendsForOneFrame {
 		delete(theSourceBackendsForOneFrame, b)

internal/processtest/testdata/issue2716.go

@@ -0,0 +1,79 @@
+// Copyright 2023 The Ebitengine 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.
+
+//go:build ignore
+
+package main
+
+import (
+	"fmt"
+	"image/color"
+
+	"github.com/hajimehoshi/ebiten/v2"
+)
+
+type Game struct {
+	count int
+
+	imgs []*ebiten.Image
+}
+
+func (g *Game) Update() error {
+	const (
+		w = 16
+		h = 16
+	)
+
+	g.count++
+	if g.count >= 16 {
+		for c, img := range g.imgs {
+			for j := 0; j < h; j++ {
+				for i := 0; i < h; i++ {
+					got := img.At(i, j).(color.RGBA)
+					want := color.RGBA{byte(c), byte(c), byte(c), byte(c)}
+					if got != want {
+						return fmt.Errorf("index: %d, got: %v, want: %v", c, got, want)
+					}
+				}
+			}
+		}
+		return ebiten.Termination
+	}
+
+	pix := make([]byte, 4*w*h)
+	c := byte(len(g.imgs))
+	for i := range pix {
+		pix[i] = c
+	}
+
+	img := ebiten.NewImage(w, h)
+	img.WritePixels(pix)
+
+	g.imgs = append(g.imgs, img)
+
+	return nil
+}
+
+func (g *Game) Draw(screen *ebiten.Image) {
+}
+
+func (g *Game) Layout(width, height int) (int, int) {
+	return width, height
+}
+
+func main() {
+	if err := ebiten.RunGame(&Game{}); err != nil {
+		panic(err)
+	}
+}