op/paint: skip zero images

Updates gio#235

Signed-off-by: Elias Naur <mail@eliasnaur.com>

gpu/internal/rendertest/render_test.go

@@ -340,6 +340,16 @@ func TestLinearGradientAngled(t *testing.T) {
 	}, func(r result) {})
 }
 
+func TestZeroImage(t *testing.T) {
+	ops := new(op.Ops)
+	w := newWindow(t, 10, 10)
+	paint.ImageOp{}.Add(ops)
+	paint.PaintOp{}.Add(ops)
+	if err := w.Frame(ops); err != nil {
+		t.Error(err)
+	}
+}
+
 // lerp calculates linear interpolation with color b and p.
 func lerp(a, b f32color.RGBA, p float32) f32color.RGBA {
 	return f32color.RGBA{

gpu/internal/rendertest/util_test.go

@@ -70,7 +70,7 @@ func drawImage(t *testing.T, size int, ops *op.Ops, draw func(o *op.Ops)) (im *i
 }
 
 func run(t *testing.T, f func(o *op.Ops), c func(r result)) {
-	// draw a few times and check that it is correct each time, to
+	// Draw a few times and check that it is correct each time, to
 	// ensure any caching effects still generate the correct images.
 	var img *image.RGBA
 	var err error
@@ -82,7 +82,7 @@ func run(t *testing.T, f func(o *op.Ops), c func(r result)) {
 			t.Error("error rendering:", err)
 			return
 		}
-		// check for a reference image and make sure we are identical.
+		// Check for a reference image and make sure it is identical.
 		if !verifyRef(t, img, 0) {
 			name := fmt.Sprintf("%s-%d-bad.png", t.Name(), i)
 			if err := saveImage(name, img); err != nil {