widget,text: move Label and Editor from text to widget package

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

widget/label.go

@@ -0,0 +1,184 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package widget
+
+import (
+	"fmt"
+	"image"
+	"unicode/utf8"
+
+	"gioui.org/f32"
+	"gioui.org/layout"
+	"gioui.org/op"
+	"gioui.org/op/paint"
+	"gioui.org/text"
+
+	"golang.org/x/image/math/fixed"
+)
+
+// Label is a widget for laying out and drawing text.
+type Label struct {
+	// Alignment specify the text alignment.
+	Alignment text.Alignment
+	// MaxLines limits the number of lines. Zero means no limit.
+	MaxLines int
+}
+
+type lineIterator struct {
+	Lines     []text.Line
+	Clip      image.Rectangle
+	Alignment text.Alignment
+	Width     int
+	Offset    image.Point
+
+	y, prevDesc fixed.Int26_6
+}
+
+const inf = 1e6
+
+func (l *lineIterator) Next() (text.String, f32.Point, bool) {
+	for len(l.Lines) > 0 {
+		line := l.Lines[0]
+		l.Lines = l.Lines[1:]
+		x := align(l.Alignment, line.Width, l.Width) + fixed.I(l.Offset.X)
+		l.y += l.prevDesc + line.Ascent
+		l.prevDesc = line.Descent
+		// Align baseline and line start to the pixel grid.
+		off := fixed.Point26_6{X: fixed.I(x.Floor()), Y: fixed.I(l.y.Ceil())}
+		l.y = off.Y
+		off.Y += fixed.I(l.Offset.Y)
+		if (off.Y + line.Bounds.Min.Y).Floor() > l.Clip.Max.Y {
+			break
+		}
+		if (off.Y + line.Bounds.Max.Y).Ceil() < l.Clip.Min.Y {
+			continue
+		}
+		str := line.Text
+		for len(str.Advances) > 0 {
+			adv := str.Advances[0]
+			if (off.X + adv + line.Bounds.Max.X - line.Width).Ceil() >= l.Clip.Min.X {
+				break
+			}
+			off.X += adv
+			_, s := utf8.DecodeRuneInString(str.String)
+			str.String = str.String[s:]
+			str.Advances = str.Advances[1:]
+		}
+		n := 0
+		endx := off.X
+		for i, adv := range str.Advances {
+			if (endx + line.Bounds.Min.X).Floor() > l.Clip.Max.X {
+				str.String = str.String[:n]
+				str.Advances = str.Advances[:i]
+				break
+			}
+			_, s := utf8.DecodeRuneInString(str.String[n:])
+			n += s
+			endx += adv
+		}
+		offf := f32.Point{X: float32(off.X) / 64, Y: float32(off.Y) / 64}
+		return str, offf, true
+	}
+	return text.String{}, f32.Point{}, false
+}
+
+func (l Label) Layout(gtx *layout.Context, s *text.Shaper, font text.Font, txt string) {
+	cs := gtx.Constraints
+	textLayout := s.Layout(gtx, font, txt, text.LayoutOptions{MaxWidth: cs.Width.Max})
+	lines := textLayout.Lines
+	if max := l.MaxLines; max > 0 && len(lines) > max {
+		lines = lines[:max]
+	}
+	dims := linesDimens(lines)
+	dims.Size = cs.Constrain(dims.Size)
+	clip := textPadding(lines)
+	clip.Max = clip.Max.Add(dims.Size)
+	it := lineIterator{
+		Lines:     lines,
+		Clip:      clip,
+		Alignment: l.Alignment,
+		Width:     dims.Size.X,
+	}
+	for {
+		str, off, ok := it.Next()
+		if !ok {
+			break
+		}
+		lclip := toRectF(clip).Sub(off)
+		var stack op.StackOp
+		stack.Push(gtx.Ops)
+		op.TransformOp{}.Offset(off).Add(gtx.Ops)
+		s.Shape(gtx, font, str).Add(gtx.Ops)
+		paint.PaintOp{Rect: lclip}.Add(gtx.Ops)
+		stack.Pop()
+	}
+	gtx.Dimensions = dims
+}
+
+func toRectF(r image.Rectangle) f32.Rectangle {
+	return f32.Rectangle{
+		Min: f32.Point{X: float32(r.Min.X), Y: float32(r.Min.Y)},
+		Max: f32.Point{X: float32(r.Max.X), Y: float32(r.Max.Y)},
+	}
+}
+
+func textPadding(lines []text.Line) (padding image.Rectangle) {
+	if len(lines) == 0 {
+		return
+	}
+	first := lines[0]
+	if d := first.Ascent + first.Bounds.Min.Y; d < 0 {
+		padding.Min.Y = d.Ceil()
+	}
+	last := lines[len(lines)-1]
+	if d := last.Bounds.Max.Y - last.Descent; d > 0 {
+		padding.Max.Y = d.Ceil()
+	}
+	if d := first.Bounds.Min.X; d < 0 {
+		padding.Min.X = d.Ceil()
+	}
+	if d := first.Bounds.Max.X - first.Width; d > 0 {
+		padding.Max.X = d.Ceil()
+	}
+	return
+}
+
+func linesDimens(lines []text.Line) layout.Dimensions {
+	var width fixed.Int26_6
+	var h int
+	var baseline int
+	if len(lines) > 0 {
+		baseline = lines[0].Ascent.Ceil()
+		var prevDesc fixed.Int26_6
+		for _, l := range lines {
+			h += (prevDesc + l.Ascent).Ceil()
+			prevDesc = l.Descent
+			if l.Width > width {
+				width = l.Width
+			}
+		}
+		h += lines[len(lines)-1].Descent.Ceil()
+	}
+	w := width.Ceil()
+	return layout.Dimensions{
+		Size: image.Point{
+			X: w,
+			Y: h,
+		},
+		Baseline: baseline,
+	}
+}
+
+func align(align text.Alignment, width fixed.Int26_6, maxWidth int) fixed.Int26_6 {
+	mw := fixed.I(maxWidth)
+	switch align {
+	case text.Middle:
+		return fixed.I(((mw - width) / 2).Floor())
+	case text.End:
+		return fixed.I((mw - width).Floor())
+	case text.Start:
+		return 0
+	default:
+		panic(fmt.Errorf("unknown alignment %v", align))
+	}
+}