internal/atlas: bug fix: respect injected maxSize for testings

internal/atlas/image.go

@@ -745,6 +745,10 @@ func (i *Image) allocate(putOnAtlas bool) {
 	}
 
 	if !putOnAtlas || !i.canBePutOnAtlas() {
+		if i.width+2*i.paddingSize() > maxSize || i.height+2*i.paddingSize() > maxSize {
+			panic(fmt.Sprintf("atlas: the image being put on an atlas is too big: width: %d, height: %d", i.width, i.height))
+		}
+
 		typ := restorable.ImageTypeRegular
 		if i.imageType == ImageTypeVolatile {
 			typ = restorable.ImageTypeVolatile
@@ -815,8 +819,14 @@ func BeginFrame(graphicsDriver graphicsdriver.Graphics) error {
 		if len(theBackends) != 0 {
 			panic("atlas: all the images must be not on an atlas before the game starts")
 		}
-		minSize = 1024
-		maxSize = restorable.MaxImageSize(graphicsDriver)
+
+		// minSize and maxSize can already be set for testings.
+		if minSize == 0 {
+			minSize = 1024
+		}
+		if maxSize == 0 {
+			maxSize = restorable.MaxImageSize(graphicsDriver)
+		}
 	})
 	if err != nil {
 		return err

internal/atlas/image_test.go

@@ -561,6 +561,21 @@ func Disable_TestMinImageSize(t *testing.T) {
 	img.ReplacePixels(make([]byte, 4*s*s), nil)
 }
 
+func TestMaxImageSizeExceeded(t *testing.T) {
+	// This tests that a too-big image is allocated correctly.
+	s := maxImageSizeForTesting
+	img := atlas.NewImage(s+1, s, atlas.ImageTypeRegular)
+	defer img.MarkDisposed()
+
+	defer func() {
+		if err := recover(); err == nil {
+			t.Errorf("ReplacePixels must panic but not")
+		}
+	}()
+
+	img.ReplacePixels(make([]byte, 4*(s+1)*s), nil)
+}
+
 // Issue #1421
 func TestDisposedAndReputOnAtlas(t *testing.T) {
 	const size = 16