gpu: don't store transformed rectangle paths under the same cache key

Fixes incorrect rendering of multiple transformed instances of a
rectangle.

Fixes: https://todo.sr.ht/~eliasnaur/gio/635
Signed-off-by: Elias Naur <mail@eliasnaur.com>

gpu/gpu.go

@@ -1055,6 +1055,7 @@ loop:
 			} else {
 				quads.aux, bounds, _ = d.boundsForTransformedRect(bounds, trans)
 				quads.key = opKey{Key: encOp.Key}
+				quads.key = quads.key.SetTransform(trans)
 			}
 			d.addClipPath(&state, quads.aux, quads.key, bounds, off)
 			quads = quadsOp{}
@@ -1100,7 +1101,7 @@ loop:
 				// The paint operation is sheared or rotated, add a clip path representing
 				// this transformed rectangle.
 				k := opKey{Key: encOp.Key}
-				k.SetTransform(t) // TODO: This call has no effect.
+				k = k.SetTransform(t)
 				d.addClipPath(&state, clipData, k, bnd, off)
 			}
 

gpu/internal/rendertest/clip_test.go

@@ -293,3 +293,20 @@ func TestStrokedRect(t *testing.T) {
 	}, func(r result) {
 	})
 }
+
+func TestInstancedRects(t *testing.T) {
+	run(t, func(o *op.Ops) {
+		macro := op.Record(o)
+		clip := clip.Rect{Max: image.Pt(20, 20)}.Push(o)
+		paint.ColorOp{Color: color.NRGBA{R: 0x80, A: 0xFF}}.Add(o)
+		paint.PaintOp{}.Add(o)
+		clip.Pop()
+		c := macro.Stop()
+
+		for i := 0; i < 2; i++ {
+			op.Affine(f32.Affine2D{}.Rotate(f32.Pt(0, 0), .2)).Add(o)
+			c.Add(o)
+			op.Offset(image.Pt(20, 20)).Add(o)
+		}
+	}, nil)
+}