op/clip,gpu: move approximation of complex strokes to op/clip.Op.Add

Before this change, the two renderers both had special case code for
approximating strokes they don't support natively. This change moves
that conversion to clip.Op.Add, for several reasons:

- The compute renderer no longer need fallback logic and caches for
  strokes it doesn't support.
- The approximation logic is slow. Moving it to clip.Op.Add will not
  speed it up, but will make the cost easier to spot in profiles. Until all
  strokes are supported natively, users can use macros to cache
  expensive strokes.
- Reduced garbage: Op.Add takes an op.Ops anyway, and can use that for
  storing the approximated stroke outline.

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

gpu/compute.go

@@ -18,10 +18,8 @@ import (
 	"gioui.org/internal/f32color"
 	"gioui.org/internal/ops"
 	"gioui.org/internal/scene"
-	"gioui.org/internal/stroke"
 	"gioui.org/layout"
 	"gioui.org/op"
-	"gioui.org/op/clip"
 )
 
 type compute struct {
@@ -671,9 +669,9 @@ func (g *compute) encodeClipStack(clip, bounds f32.Rectangle, p *pathOp, begin b
 		nclips += g.encodeClipStack(clip, bounds, p.parent, true)
 		nclips += 1
 	}
-	s := isStroke(p)
+	isStroke := p.stroke.Width > 0
 	if p != nil && p.path {
-		if s {
+		if isStroke {
 			g.enc.fillMode(scene.FillModeStroke)
 			g.enc.lineWidth(p.stroke.Width)
 		}
@@ -685,7 +683,7 @@ func (g *compute) encodeClipStack(clip, bounds f32.Rectangle, p *pathOp, begin b
 	}
 	if begin {
 		g.enc.beginClip(clip)
-		if s {
+		if isStroke {
 			g.enc.fillMode(scene.FillModeNonzero)
 		}
 		if p != nil && p.path {
@@ -695,31 +693,8 @@ func (g *compute) encodeClipStack(clip, bounds f32.Rectangle, p *pathOp, begin b
 	return nclips
 }
 
-func supportsStroke(p *pathOp) bool {
-	return stroke.IsSolidLine(p.dashes) && p.stroke.Miter == 0 && p.stroke.Join == clip.RoundJoin && p.stroke.Cap == clip.RoundCap
-}
-
-func isStroke(p *pathOp) bool {
-	return p.stroke.Width > 0 && supportsStroke(p)
-}
-
-func encodePath(p *pathOp) encoder {
+func encodePath(verts []byte) encoder {
 	var enc encoder
-	verts := p.pathVerts
-	if p.stroke.Width > 0 && !supportsStroke(p) {
-		ss := stroke.StrokeStyle{
-			Width: p.stroke.Width,
-			Miter: p.stroke.Miter,
-			Cap:   stroke.StrokeCap(p.stroke.Cap),
-			Join:  stroke.StrokeJoin(p.stroke.Join),
-		}
-		quads := stroke.StrokePathCommands(ss, p.dashes, verts)
-		for _, quad := range quads {
-			q := quad.Quad
-			enc.quad(q.From, q.Ctrl, q.To)
-		}
-		return enc
-	}
 	for len(verts) >= scene.CommandSize+4 {
 		cmd := ops.DecodeCommand(verts[4:])
 		enc.scene = append(enc.scene, cmd)