ui: build paths as ops

Instead of allocating and constructing a clip path, store path data
directly in op lists. Use separate op lists for cached text layout
paths.

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

ui/text/editor.go

@@ -10,7 +10,6 @@ import (
 
 	"gioui.org/ui"
 	"gioui.org/ui/draw"
-	"gioui.org/ui/f32"
 	"gioui.org/ui/gesture"
 	"gioui.org/ui/key"
 	"gioui.org/ui/layout"
@@ -49,11 +48,6 @@ type Editor struct {
 	clicker gesture.Click
 }
 
-type linePath struct {
-	path *draw.Path
-	off  f32.Point
-}
-
 const (
 	blinksPerSecond  = 1
 	maxBlinkDuration = 10 * time.Second
@@ -170,10 +164,9 @@ func (e *Editor) Layout(ops *ui.Ops, cs layout.Constraints) layout.Dimens {
 		if !ok {
 			break
 		}
-		path := e.Face.Path(str)
 		ui.OpPush{}.Add(ops)
 		ui.OpTransform{Transform: ui.Offset(lineOff)}.Add(ops)
-		draw.OpClip{Path: path}.Add(ops)
+		e.Face.Path(str).Add(ops)
 		draw.OpDraw{Rect: toRectF(clip).Sub(lineOff)}.Add(ops)
 		ui.OpPop{}.Add(ops)
 	}

ui/text/label.go

@@ -100,11 +100,10 @@ func (l Label) Layout(ops *ui.Ops, cs layout.Constraints) layout.Dimens {
 		if !ok {
 			break
 		}
-		path := l.Face.Path(str)
 		lclip := toRectF(clip).Sub(off)
 		ui.OpPush{}.Add(ops)
 		ui.OpTransform{Transform: ui.Offset(off)}.Add(ops)
-		draw.OpClip{Path: path}.Add(ops)
+		l.Face.Path(str).Add(ops)
 		draw.OpDraw{Rect: lclip}.Add(ops)
 		ui.OpPop{}.Add(ops)
 	}

ui/text/measure.go

@@ -6,7 +6,7 @@ import (
 	"fmt"
 	"image"
 
-	"gioui.org/ui/draw"
+	"gioui.org/ui"
 	"gioui.org/ui/layout"
 	"golang.org/x/image/math/fixed"
 )
@@ -35,7 +35,7 @@ type Layout struct {
 
 type Face interface {
 	Layout(str string, singleLine bool, maxWidth int) *Layout
-	Path(str String) *draw.Path
+	Path(str String) ui.OpBlock
 }
 
 type Alignment uint8