restorable: Fix clearing logic

Fixes #740

image_test.go

@@ -524,6 +524,36 @@ func TestImageFill(t *testing.T) {
 	}
 }
 
+// Issue #740
+func TestImageClear(t *testing.T) {
+	const w, h = 128, 256
+	img, err := NewImage(w, h, FilterNearest)
+	if err != nil {
+		t.Fatal(err)
+		return
+	}
+	img.Fill(color.White)
+	for j := 0; j < h; j++ {
+		for i := 0; i < w; i++ {
+			got := img.At(i, j)
+			want := color.RGBA{0xff, 0xff, 0xff, 0xff}
+			if got != want {
+				t.Errorf("img At(%d, %d): got %#v; want %#v", i, j, got, want)
+			}
+		}
+	}
+	img.Clear()
+	for j := 0; j < h; j++ {
+		for i := 0; i < w; i++ {
+			got := img.At(i, j)
+			want := color.RGBA{}
+			if got != want {
+				t.Errorf("img At(%d, %d): got %#v; want %#v", i, j, got, want)
+			}
+		}
+	}
+}
+
 // Issue #317, #558, #724
 func TestImageEdge(t *testing.T) {
 	const (

internal/restorable/image.go

@@ -157,9 +157,11 @@ func (i *Image) ReplacePixels(pixels []byte, x, y, width, height int) {
 		// This means dummyImage might not be restored yet when this image is restored.
 		// However, that's ok since this image will be stale or have updated pixel data
 		// and this image can be restored without dummyImage.
-		w, h := dummyImage.Size()
-		vs := graphics.QuadVertices(w, h, 0, 0, w, h,
-			float32(width)/float32(w), 0, 0, float32(height)/float32(h),
+		dw, dh := dummyImage.Size()
+		w2 := graphics.NextPowerOf2Int(w)
+		h2 := graphics.NextPowerOf2Int(h)
+		vs := graphics.QuadVertices(w2, h2, 0, 0, dw, dh,
+			float32(width)/float32(dw), 0, 0, float32(height)/float32(dh),
 			float32(x), float32(y),
 			0, 0, 0, 0)
 		is := graphics.QuadIndices()