op/clip: split Rect into pixel-aligned Rect and rounded RRect

The pixel-aligned Rect is more efficient and easier to use in the common case
of layout clipping.

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

widget/material/switch.go

@@ -56,7 +56,7 @@ func (s SwitchStyle) Layout(gtx layout.Context) layout.Dimensions {
 	}
 	trackColor := mulAlpha(col, 150)
 	op.Offset(f32.Point{Y: trackOff}).Add(gtx.Ops)
-	clip.Rect{
+	clip.RRect{
 		Rect: trackRect,
 		NE:   trackCorner, NW: trackCorner, SE: trackCorner, SW: trackCorner,
 	}.Add(gtx.Ops)
@@ -74,7 +74,7 @@ func (s SwitchStyle) Layout(gtx layout.Context) layout.Dimensions {
 	}
 	op.Offset(inkOff).Add(gtx.Ops)
 	gtx.Constraints.Min = image.Pt(inkSize, inkSize)
-	clip.Rect{
+	clip.RRect{
 		Rect: f32.Rectangle{
 			Max: layout.FPt(gtx.Constraints.Min),
 		},
@@ -127,7 +127,7 @@ func drawDisc(ops *op.Ops, sz float32, col color.RGBA) {
 	defer op.Push(ops).Pop()
 	rr := sz / 2
 	r := f32.Rectangle{Max: f32.Point{X: sz, Y: sz}}
-	clip.Rect{
+	clip.RRect{
 		Rect: r,
 		NE:   rr, NW: rr, SE: rr, SW: rr,
 	}.Add(ops)