op/clip: replace Rect and RoundRect with Rect type

Remembering the order of the corners in the RoundRect is difficult,
which suggest that RoundRect should be a struct with named fields.

Do that, and make Rect the special case where corner radii are all
zero.

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

layout/list.go

@@ -249,7 +249,7 @@ func (l *List) layout() Dimensions {
 		}
 		var stack op.StackOp
 		stack.Push(ops)
-		clip.Rect(ops, toRectF(r)).Add(ops)
+		clip.Rect{Rect: toRectF(r)}.Op(ops).Add(ops)
 		op.TransformOp{}.Offset(toPointF(axisPoint(l.Axis, pos, cross))).Add(ops)
 		child.macro.Add(ops)
 		stack.Pop()

op/clip/clip.go

@@ -284,25 +284,38 @@ func (p *Path) End() Op {
 	}
 }
 
-// Rect returns the clip area of a rectangle.
-func Rect(ops *op.Ops, r f32.Rectangle) Op {
-	ri := image.Rectangle{
-		Min: image.Point{X: int(r.Min.X), Y: int(r.Min.Y)},
-		Max: image.Point{X: int(r.Max.X), Y: int(r.Max.Y)},
-	}
-	// Optimize pixel-aligned rectangles to just its bounds.
-	if r == toRectF(ri) {
-		return Op{bounds: r}
-	}
-	return RoundRect(ops, r, 0, 0, 0, 0)
-}
-
-// RoundRect returns the clip area of a rectangle with rounded
-// corners defined by their radii. The origin is in the upper left
+// Rect represents the clip area of a rectangle with rounded
+// corners.The origin is in the upper left
 // corner.
 // Specify a square with corner radii equal to half the square size to
 // construct a circular clip area.
-func RoundRect(ops *op.Ops, r f32.Rectangle, se, sw, nw, ne float32) Op {
+type Rect struct {
+	Rect f32.Rectangle
+	// The corner radii.
+	SE, SW, NW, NE float32
+}
+
+// Op returns the Op for the rectangle.
+func (rr Rect) Op(ops *op.Ops) Op {
+	r := rr.Rect
+	// Optimize for the common pixel aligned rectangle with no
+	// corner rounding.
+	if rr.SE == 0 && rr.SW == 0 && rr.NW == 0 && rr.NE == 0 {
+		ri := image.Rectangle{
+			Min: image.Point{X: int(r.Min.X), Y: int(r.Min.Y)},
+			Max: image.Point{X: int(r.Max.X), Y: int(r.Max.Y)},
+		}
+		// Optimize pixel-aligned rectangles to just its bounds.
+		if r == toRectF(ri) {
+			return Op{bounds: r}
+		}
+	}
+	return roundRect(ops, r, rr.SE, rr.SW, rr.NW, rr.NE)
+}
+
+// roundRect returns the clip area of a rectangle with rounded
+// corners defined by their radii.
+func roundRect(ops *op.Ops, r f32.Rectangle, se, sw, nw, ne float32) Op {
 	size := r.Size()
 	// https://pomax.github.io/bezierinfo/#circles_cubic.
 	w, h := float32(size.X), float32(size.Y)

widget/material/button.go

@@ -77,13 +77,13 @@ func (b Button) Layout(gtx *layout.Context, button *widget.Button) {
 	})
 	bg := st.Expand(gtx, func() {
 		rr := float32(gtx.Px(unit.Dp(4)))
-		clip.RoundRect(gtx.Ops,
-			f32.Rectangle{Max: f32.Point{
+		clip.Rect{
+			Rect: f32.Rectangle{Max: f32.Point{
 				X: float32(gtx.Constraints.Width.Min),
 				Y: float32(gtx.Constraints.Height.Min),
 			}},
-			rr, rr, rr, rr,
-		).Add(gtx.Ops)
+			NE: rr, NW: rr, SE: rr, SW: rr,
+		}.Op(gtx.Ops).Add(gtx.Ops)
 		fill(gtx, bgcol)
 		for _, c := range button.History() {
 			drawInk(gtx, c)
@@ -112,10 +112,10 @@ func (b IconButton) Layout(gtx *layout.Context, button *widget.Button) {
 	bg := st.Expand(gtx, func() {
 		size := float32(gtx.Constraints.Width.Min)
 		rr := float32(size) * .5
-		clip.RoundRect(gtx.Ops,
-			f32.Rectangle{Max: f32.Point{X: size, Y: size}},
-			rr, rr, rr, rr,
-		).Add(gtx.Ops)
+		clip.Rect{
+			Rect: f32.Rectangle{Max: f32.Point{X: size, Y: size}},
+			NE:   rr, NW: rr, SE: rr, SW: rr,
+		}.Op(gtx.Ops).Add(gtx.Ops)
 		fill(gtx, bgcol)
 		for _, c := range button.History() {
 			drawInk(gtx, c)
@@ -154,10 +154,13 @@ func drawInk(gtx *layout.Context, c widget.Click) {
 		X: -rr,
 		Y: -rr,
 	}).Add(gtx.Ops)
-	clip.RoundRect(gtx.Ops, f32.Rectangle{Max: f32.Point{
-		X: float32(size),
-		Y: float32(size),
-	}}, rr, rr, rr, rr).Add(gtx.Ops)
+	clip.Rect{
+		Rect: f32.Rectangle{Max: f32.Point{
+			X: float32(size),
+			Y: float32(size),
+		}},
+		NE: rr, NW: rr, SE: rr, SW: rr,
+	}.Op(gtx.Ops).Add(gtx.Ops)
 	paint.PaintOp{Rect: f32.Rectangle{Max: f32.Point{X: float32(size), Y: float32(size)}}}.Add(gtx.Ops)
 	stack.Pop()
 	op.InvalidateOp{}.Add(gtx.Ops)

widget/material/image.go

@@ -37,7 +37,7 @@ func (im Image) Layout(gtx *layout.Context) {
 	d := image.Point{X: cs.Width.Constrain(w), Y: cs.Height.Constrain(h)}
 	var s op.StackOp
 	s.Push(gtx.Ops)
-	clip.Rect(gtx.Ops, f32.Rectangle{Max: toPointF(d)}).Add(gtx.Ops)
+	clip.Rect{Rect: f32.Rectangle{Max: toPointF(d)}}.Op(gtx.Ops).Add(gtx.Ops)
 	im.Src.Add(gtx.Ops)
 	paint.PaintOp{Rect: f32.Rectangle{Max: f32.Point{X: float32(w), Y: float32(h)}}}.Add(gtx.Ops)
 	s.Pop()