shareable: Bug fix: wrong size calculation

The size calculation must consider the paddings.

Fixes #1217

internal/shareable/export_test.go

@@ -18,6 +18,29 @@ func MakeImagesSharedForTesting() error {
 	return makeImagesShared()
 }
 
+var (
+	oldMinSize int
+	oldMaxSize int
+)
+
+func SetImageSizeForTesting(min, max int) {
+	oldMinSize = min
+	oldMaxSize = max
+	minSize = min
+	maxSize = max
+}
+
+func ResetImageSizeForTesting() {
+	minSize = oldMinSize
+	maxSize = oldMaxSize
+}
+
+func ResetBackendsForTesting() {
+	backendsM.Lock()
+	defer backendsM.Unlock()
+	theBackends = nil
+}
+
 func (i *Image) IsSharedForTesting() bool {
 	backendsM.Lock()
 	defer backendsM.Unlock()

internal/shareable/image.go

@@ -573,7 +573,7 @@ func (i *Image) shareable() bool {
 	if i.screen {
 		return false
 	}
-	return i.width <= maxSize && i.height <= maxSize
+	return i.width+2*paddingSize <= maxSize && i.height+2*paddingSize <= maxSize
 }
 
 func (i *Image) allocate(shareable bool) {
@@ -606,7 +606,7 @@ func (i *Image) allocate(shareable bool) {
 		}
 	}
 	size := minSize
-	for i.width > size || i.height > size {
+	for i.width+2*paddingSize > size || i.height+2*paddingSize > size {
 		if size == maxSize {
 			panic(fmt.Sprintf("shareable: the image being shared is too big: width: %d, height: %d", i.width, i.height))
 		}

internal/shareable/image_test.go

@@ -25,7 +25,14 @@ import (
 	t "github.com/hajimehoshi/ebiten/internal/testing"
 )
 
+const (
+	minImageSizeForTesting = 1024
+	maxImageSizeForTesting = 4096
+)
+
 func TestMain(m *testing.M) {
+	SetImageSizeForTesting(minImageSizeForTesting, maxImageSizeForTesting)
+	defer ResetImageSizeForTesting()
 	t.MainWithRunLoop(m)
 }
 
@@ -451,4 +458,25 @@ func TestExtendWithBigImage(t *testing.T) {
 	img1.ReplacePixels(make([]byte, 4*1025*1025))
 }
 
+// Issue #1217
+func TestMaxImageSize(t *testing.T) {
+	// This tests that a too-big image is allocated correctly.
+	s := maxImageSizeForTesting
+	img := NewImage(s, s, false)
+	defer img.MarkDisposed()
+	img.ReplacePixels(make([]byte, 4*s*s))
+}
+
+// Issue #1217
+func TestMinImageSize(t *testing.T) {
+	ResetBackendsForTesting()
+
+	// This tests that extending a backend works correctly.
+	// Though the image size is minimum size of the backend, extending the backend happens due to the paddings.
+	s := minImageSizeForTesting
+	img := NewImage(s, s, false)
+	defer img.MarkDisposed()
+	img.ReplacePixels(make([]byte, 4*s*s))
+}
+
 // TODO: Add tests to extend shareable image out of the main loop