ui/text: use BlockOp as materials

Before this change, clients were expected to set up the current
material (color or image) before laying out Labels and Editors.
This was done to avoid garbage from a hypothetical material
interface covering both colors and images.

However, some widgets need more than one material: the Editor had
HintImage for the hint text material.

This change implements generalized materials through blocks:
anywhere a material is expected, a ui.BlockOp is is assumed to
contain the operation(s) needed for setting the desired material.

This way we avoid allocations (interfaces) and keep the
abstraction over material types.

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

ui/ops.go

@@ -213,6 +213,9 @@ func (b *BlockOp) decode(data []byte, refs []interface{}) {
 }
 
 func (b BlockOp) Add(o *Ops) {
+	if b.ops == nil {
+		return
+	}
 	data := make([]byte, ops.TypeBlockLen)
 	data[0] = byte(ops.TypeBlock)
 	bo := binary.LittleEndian

ui/text/editor.go

@@ -27,8 +27,9 @@ type Editor struct {
 	SingleLine bool
 	Submit     bool
 
-	Hint      string
-	HintImage image.Image
+	Material     ui.BlockOp
+	Hint         string
+	HintMaterial ui.BlockOp
 
 	oldCfg            ui.Config
 	blinkStart        time.Time
@@ -202,8 +203,10 @@ func (e *Editor) Layout(ops *ui.Ops, cs layout.Constraints) layout.Dimens {
 		Offset:    off,
 	}
 	ui.PushOp{}.Add(ops)
-	if e.HintImage != nil && e.rr.len() == 0 {
-		draw.ImageOp{Img: e.HintImage, Rect: e.HintImage.Bounds()}.Add(ops)
+	if e.rr.len() > 0 {
+		e.Material.Add(ops)
+	} else {
+		e.HintMaterial.Add(ops)
 	}
 	for {
 		str, lineOff, ok := e.it.Next()
@@ -216,7 +219,6 @@ func (e *Editor) Layout(ops *ui.Ops, cs layout.Constraints) layout.Dimens {
 		draw.DrawOp{Rect: toRectF(clip).Sub(lineOff)}.Add(ops)
 		ui.PopOp{}.Add(ops)
 	}
-	ui.PopOp{}.Add(ops)
 	if e.focused {
 		now := e.Config.Now
 		dt := now.Sub(e.blinkStart)
@@ -246,6 +248,7 @@ func (e *Editor) Layout(ops *ui.Ops, cs layout.Constraints) layout.Dimens {
 			redraw.Add(ops)
 		}
 	}
+	ui.PopOp{}.Add(ops)
 
 	baseline := e.padTop + e.dims.Baseline
 	pointer.AreaRect(e.viewSize).Add(ops)

ui/text/label.go

@@ -17,6 +17,7 @@ import (
 
 type Label struct {
 	Face      Face
+	Material  ui.BlockOp
 	Alignment Alignment
 	Text      string
 	MaxLines  int
@@ -108,6 +109,7 @@ func (l Label) Layout(ops *ui.Ops, cs layout.Constraints) layout.Dimens {
 		ui.PushOp{}.Add(ops)
 		ui.TransformOp{Transform: ui.Offset(off)}.Add(ops)
 		l.Face.Path(str).Add(ops)
+		l.Material.Add(ops)
 		draw.DrawOp{Rect: lclip}.Add(ops)
 		ui.PopOp{}.Add(ops)
 	}