text: simplify text layout and shaping API

First, replace LayoutOptions with an explicit maximum width parameter.  The
single-field option struct doesn't carry its weight, and I don't think we'll
see more global layout options in the future. Rather, I expect options to cover
spans of text or be part of a Font.

Second, replace the unit.Converter with an scaled text size. It's simpler and
allow the Editor and similar widgets to easily detect whether their cached
layouts are stale. Package text no longer depends on package unit, which is
now dealt with at the widget-level only.

Finally, remove the Size field from Font. It was a design mistake: a Font is
assumed to cover all sizes, as evidenced by the FontRegistry disregarding
Size when looking up fonts.

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

font/opentype/opentype.go

@@ -85,12 +85,12 @@ func (c *Collection) Font(i int) (*Font, error) {
 	return &Font{font: fnt}, nil
 }
 
-func (f *Font) Layout(ppem fixed.Int26_6, txt io.Reader, opts text.LayoutOptions) ([]text.Line, error) {
+func (f *Font) Layout(ppem fixed.Int26_6, maxWidth int, txt io.Reader) ([]text.Line, error) {
 	glyphs, err := readGlyphs(txt)
 	if err != nil {
 		return nil, err
 	}
-	return layoutText(&f.buf, ppem, &opentype{Font: f.font, Hinting: font.HintingFull}, glyphs, opts)
+	return layoutText(&f.buf, ppem, maxWidth, &opentype{Font: f.font, Hinting: font.HintingFull}, glyphs)
 }
 
 func (f *Font) Shape(ppem fixed.Int26_6, str []text.Glyph) op.CallOp {
@@ -102,7 +102,7 @@ func (f *Font) Metrics(ppem fixed.Int26_6) font.Metrics {
 	return o.Metrics(&f.buf, ppem)
 }
 
-func layoutText(sbuf *sfnt.Buffer, ppem fixed.Int26_6, f *opentype, glyphs []text.Glyph, opts text.LayoutOptions) ([]text.Line, error) {
+func layoutText(sbuf *sfnt.Buffer, ppem fixed.Int26_6, maxWidth int, f *opentype, glyphs []text.Glyph) ([]text.Line, error) {
 	m := f.Metrics(sbuf, ppem)
 	lineTmpl := text.Line{
 		Ascent: m.Ascent,
@@ -112,7 +112,7 @@ func layoutText(sbuf *sfnt.Buffer, ppem fixed.Int26_6, f *opentype, glyphs []tex
 		Bounds:  f.Bounds(sbuf, ppem),
 	}
 	var lines []text.Line
-	maxDotX := fixed.I(opts.MaxWidth)
+	maxDotX := fixed.I(maxWidth)
 	type state struct {
 		r     rune
 		adv   fixed.Int26_6

text/lru.go

@@ -30,9 +30,9 @@ type path struct {
 }
 
 type layoutKey struct {
-	ppem fixed.Int26_6
-	str  string
-	opts LayoutOptions
+	ppem     fixed.Int26_6
+	maxWidth int
+	str      string
 }
 
 type pathKey struct {

text/shaper.go

@@ -9,24 +9,23 @@ import (
 	"golang.org/x/image/font"
 
 	"gioui.org/op"
-	"gioui.org/unit"
 	"golang.org/x/image/math/fixed"
 )
 
 // Shaper implements layout and shaping of text.
 type Shaper interface {
 	// Layout a text according to a set of options.
-	Layout(c unit.Converter, font Font, txt io.Reader, opts LayoutOptions) ([]Line, error)
+	Layout(font Font, size fixed.Int26_6, maxWidth int, txt io.Reader) ([]Line, error)
 	// Shape a line of text and return a clipping operation for its outline.
-	Shape(c unit.Converter, font Font, layout []Glyph) op.CallOp
+	Shape(font Font, size fixed.Int26_6, layout []Glyph) op.CallOp
 
 	// LayoutString is like Layout, but for strings..
-	LayoutString(c unit.Converter, font Font, str string, opts LayoutOptions) []Line
+	LayoutString(font Font, size fixed.Int26_6, maxWidth int, str string) []Line
 	// ShapeString is like Shape for lines previously laid out by LayoutString.
-	ShapeString(c unit.Converter, font Font, str string, layout []Glyph) op.CallOp
+	ShapeString(font Font, size fixed.Int26_6, str string, layout []Glyph) op.CallOp
 
 	// Metrics returns the font metrics for font.
-	Metrics(c unit.Converter, font Font) font.Metrics
+	Metrics(font Font, size fixed.Int26_6) font.Metrics
 }
 
 // FontRegistry implements layout and shaping of text from a set of
@@ -53,8 +52,6 @@ func (s *FontRegistry) Register(font Font, tf Face) {
 		s.def = font.Typeface
 		s.faces = make(map[Font]*face)
 	}
-	// Treat all font sizes equally.
-	font.Size = unit.Value{}
 	if font.Weight == 0 {
 		font.Weight = Normal
 	}
@@ -63,31 +60,29 @@ func (s *FontRegistry) Register(font Font, tf Face) {
 	}
 }
 
-func (s *FontRegistry) Layout(c unit.Converter, font Font, txt io.Reader, opts LayoutOptions) ([]Line, error) {
+func (s *FontRegistry) Layout(font Font, size fixed.Int26_6, maxWidth int, txt io.Reader) ([]Line, error) {
 	tf := s.faceForFont(font)
-	ppem := fixed.I(c.Px(font.Size))
-	return tf.face.Layout(ppem, txt, opts)
+	return tf.face.Layout(size, maxWidth, txt)
 }
 
-func (s *FontRegistry) Shape(c unit.Converter, font Font, layout []Glyph) op.CallOp {
+func (s *FontRegistry) Shape(font Font, size fixed.Int26_6, layout []Glyph) op.CallOp {
 	tf := s.faceForFont(font)
-	ppem := fixed.I(c.Px(font.Size))
-	return tf.face.Shape(ppem, layout)
+	return tf.face.Shape(size, layout)
 }
 
-func (s *FontRegistry) LayoutString(c unit.Converter, font Font, str string, opts LayoutOptions) []Line {
+func (s *FontRegistry) LayoutString(font Font, size fixed.Int26_6, maxWidth int, str string) []Line {
 	tf := s.faceForFont(font)
-	return tf.layout(fixed.I(c.Px(font.Size)), str, opts)
+	return tf.layout(size, maxWidth, str)
 }
 
-func (s *FontRegistry) ShapeString(c unit.Converter, font Font, str string, layout []Glyph) op.CallOp {
+func (s *FontRegistry) ShapeString(font Font, size fixed.Int26_6, str string, layout []Glyph) op.CallOp {
 	tf := s.faceForFont(font)
-	return tf.shape(fixed.I(c.Px(font.Size)), str, layout)
+	return tf.shape(size, str, layout)
 }
 
-func (s *FontRegistry) Metrics(c unit.Converter, font Font) font.Metrics {
+func (s *FontRegistry) Metrics(font Font, size fixed.Int26_6) font.Metrics {
 	tf := s.faceForFont(font)
-	return tf.metrics(fixed.I(c.Px(font.Size)))
+	return tf.metrics(size)
 }
 
 func (s *FontRegistry) faceForStyle(font Font) *face {
@@ -112,7 +107,6 @@ func (s *FontRegistry) faceForStyle(font Font) *face {
 }
 
 func (s *FontRegistry) faceForFont(font Font) *face {
-	font.Size = unit.Value{}
 	tf := s.faceForStyle(font)
 	if tf == nil {
 		font.Typeface = s.def
@@ -121,19 +115,19 @@ func (s *FontRegistry) faceForFont(font Font) *face {
 	return tf
 }
 
-func (t *face) layout(ppem fixed.Int26_6, str string, opts LayoutOptions) []Line {
+func (t *face) layout(ppem fixed.Int26_6, maxWidth int, str string) []Line {
 	if t == nil {
 		return nil
 	}
 	lk := layoutKey{
-		ppem: ppem,
-		str:  str,
-		opts: opts,
+		ppem:     ppem,
+		maxWidth: maxWidth,
+		str:      str,
 	}
 	if l, ok := t.layoutCache.Get(lk); ok {
 		return l
 	}
-	l, _ := t.face.Layout(ppem, strings.NewReader(str), opts)
+	l, _ := t.face.Layout(ppem, maxWidth, strings.NewReader(str))
 	t.layoutCache.Put(lk, l)
 	return l
 }

text/text.go

@@ -6,7 +6,6 @@ import (
 	"io"
 
 	"gioui.org/op"
-	"gioui.org/unit"
 	"golang.org/x/image/font"
 	"golang.org/x/image/math/fixed"
 )
@@ -32,23 +31,16 @@ type Glyph struct {
 	Advance fixed.Int26_6
 }
 
-// LayoutOptions specify the constraints of a text layout.
-type LayoutOptions struct {
-	// MaxWidth is the available width of the layout.
-	MaxWidth int
-}
-
 // Style is the font style.
 type Style int
 
 // Weight is a font weight, in CSS units.
 type Weight int
 
-// Font specify a particular typeface, style and size.
+// Font specify a particular typeface variant, style and weight.
 type Font struct {
 	Typeface Typeface
 	Variant  Variant
-	Size     unit.Value
 	Style    Style
 	// Weight is the text weight. If zero, Normal is used instead.
 	Weight Weight
@@ -56,7 +48,7 @@ type Font struct {
 
 // Face implements text layout and shaping for a particular font.
 type Face interface {
-	Layout(ppem fixed.Int26_6, txt io.Reader, opts LayoutOptions) ([]Line, error)
+	Layout(ppem fixed.Int26_6, maxWidth int, txt io.Reader) ([]Line, error)
 	Shape(ppem fixed.Int26_6, str []Glyph) op.CallOp
 	Metrics(ppem fixed.Int26_6) font.Metrics
 }

widget/editor.go

@@ -36,6 +36,7 @@ type Editor struct {
 	eventKey     int
 	scale        int
 	font         text.Font
+	textSize     fixed.Int26_6
 	blinkStart   time.Time
 	focused      bool
 	rr           editBuffer
@@ -213,14 +214,16 @@ func (e *Editor) Focus() {
 }
 
 // Layout lays out the editor.
-func (e *Editor) Layout(gtx *layout.Context, sh text.Shaper, font text.Font) {
+func (e *Editor) Layout(gtx *layout.Context, sh text.Shaper, font text.Font, size unit.Value) {
 	// Flush events from before the previous frame.
 	copy(e.events, e.events[e.prevEvents:])
 	e.events = e.events[:len(e.events)-e.prevEvents]
 	e.prevEvents = len(e.events)
-	if e.font != font {
+	textSize := fixed.I(gtx.Px(size))
+	if e.font != font || e.textSize != textSize {
 		e.invalidate()
 		e.font = font
+		e.textSize = textSize
 	}
 	e.processEvents(gtx)
 	e.layout(gtx, sh)
@@ -245,7 +248,7 @@ func (e *Editor) layout(gtx *layout.Context, sh text.Shaper) {
 	}
 
 	if !e.valid {
-		e.lines, e.dims = e.layoutText(gtx, sh, e.font)
+		e.lines, e.dims = e.layoutText(sh)
 		e.valid = true
 	}
 
@@ -277,7 +280,7 @@ func (e *Editor) layout(gtx *layout.Context, sh text.Shaper) {
 		if !ok {
 			break
 		}
-		path := sh.Shape(gtx, e.font, layout)
+		path := sh.Shape(e.font, e.textSize, layout)
 		e.shapes = append(e.shapes, line{off, path})
 	}
 
@@ -430,10 +433,9 @@ func (e *Editor) moveCoord(c unit.Converter, pos image.Point) {
 	e.moveToLine(x, carLine)
 }
 
-func (e *Editor) layoutText(c unit.Converter, s text.Shaper, font text.Font) ([]text.Line, layout.Dimensions) {
+func (e *Editor) layoutText(s text.Shaper) ([]text.Line, layout.Dimensions) {
 	e.rr.Reset()
-	opts := text.LayoutOptions{MaxWidth: e.maxWidth}
-	lines, _ := s.Layout(c, font, &e.rr, opts)
+	lines, _ := s.Layout(e.font, e.textSize, e.maxWidth, &e.rr)
 	dims := linesDimens(lines)
 	for i := 0; i < len(lines)-1; i++ {
 		// To avoid layout flickering while editing, assume a soft newline takes

widget/label.go

@@ -12,6 +12,7 @@ import (
 	"gioui.org/op"
 	"gioui.org/op/paint"
 	"gioui.org/text"
+	"gioui.org/unit"
 
 	"golang.org/x/image/math/fixed"
 )
@@ -83,9 +84,10 @@ func (l *lineIterator) Next() (int, int, []text.Glyph, f32.Point, bool) {
 	return 0, 0, nil, f32.Point{}, false
 }
 
-func (l Label) Layout(gtx *layout.Context, s text.Shaper, font text.Font, txt string) {
+func (l Label) Layout(gtx *layout.Context, s text.Shaper, font text.Font, size unit.Value, txt string) {
 	cs := gtx.Constraints
-	lines := s.LayoutString(gtx, font, txt, text.LayoutOptions{MaxWidth: cs.Width.Max})
+	textSize := fixed.I(gtx.Px(size))
+	lines := s.LayoutString(font, textSize, cs.Width.Max, txt)
 	if max := l.MaxLines; max > 0 && len(lines) > max {
 		lines = lines[:max]
 	}
@@ -109,7 +111,7 @@ func (l Label) Layout(gtx *layout.Context, s text.Shaper, font text.Font, txt st
 		stack.Push(gtx.Ops)
 		op.TransformOp{}.Offset(off).Add(gtx.Ops)
 		str := txt[start:end]
-		s.ShapeString(gtx, font, str, layout).Add(gtx.Ops)
+		s.ShapeString(font, textSize, str, layout).Add(gtx.Ops)
 		paint.PaintOp{Rect: lclip}.Add(gtx.Ops)
 		stack.Pop()
 	}

widget/material/button.go

@@ -22,6 +22,7 @@ type Button struct {
 	// Color is the text color.
 	Color        color.RGBA
 	Font         text.Font
+	TextSize     unit.Value
 	Background   color.RGBA
 	CornerRadius unit.Value
 	shaper       text.Shaper
@@ -40,10 +41,8 @@ func (t *Theme) Button(txt string) Button {
 		Text:       txt,
 		Color:      rgb(0xffffff),
 		Background: t.Color.Primary,
-		Font: text.Font{
-			Size: t.TextSize.Scale(14.0 / 16.0),
-		},
-		shaper: t.Shaper,
+		TextSize:   t.TextSize.Scale(14.0 / 16.0),
+		shaper:     t.Shaper,
 	}
 }
 
@@ -83,7 +82,7 @@ func (b Button) Layout(gtx *layout.Context, button *widget.Button) {
 			layout.Center.Layout(gtx, func() {
 				layout.Inset{Top: unit.Dp(10), Bottom: unit.Dp(10), Left: unit.Dp(12), Right: unit.Dp(12)}.Layout(gtx, func() {
 					paint.ColorOp{Color: col}.Add(gtx.Ops)
-					widget.Label{}.Layout(gtx, b.shaper, b.Font, b.Text)
+					widget.Label{}.Layout(gtx, b.shaper, b.Font, b.TextSize, b.Text)
 				})
 			})
 			pointer.Rect(image.Rectangle{Max: gtx.Dimensions.Size}).Add(gtx.Ops)

widget/material/checkable.go

@@ -18,6 +18,7 @@ type checkable struct {
 	Label              string
 	Color              color.RGBA
 	Font               text.Font
+	TextSize           unit.Value
 	IconColor          color.RGBA
 	Size               unit.Value
 	shaper             text.Shaper
@@ -56,7 +57,7 @@ func (c *checkable) layout(gtx *layout.Context, checked bool) {
 			layout.W.Layout(gtx, func() {
 				layout.UniformInset(unit.Dp(2)).Layout(gtx, func() {
 					paint.ColorOp{Color: c.Color}.Add(gtx.Ops)
-					widget.Label{}.Layout(gtx, c.shaper, c.Font, c.Label)
+					widget.Label{}.Layout(gtx, c.shaper, c.Font, c.TextSize, c.Label)
 				})
 			})
 		}),

widget/material/checkbox.go

@@ -4,7 +4,6 @@ package material
 
 import (
 	"gioui.org/layout"
-	"gioui.org/text"
 	"gioui.org/unit"
 	"gioui.org/widget"
 )
@@ -16,12 +15,10 @@ type CheckBox struct {
 func (t *Theme) CheckBox(label string) CheckBox {
 	return CheckBox{
 		checkable{
-			Label:     label,
-			Color:     t.Color.Text,
-			IconColor: t.Color.Primary,
-			Font: text.Font{
-				Size: t.TextSize.Scale(14.0 / 16.0),
-			},
+			Label:              label,
+			Color:              t.Color.Text,
+			IconColor:          t.Color.Primary,
+			TextSize:           t.TextSize.Scale(14.0 / 16.0),
 			Size:               unit.Dp(26),
 			shaper:             t.Shaper,
 			checkedStateIcon:   t.checkBoxCheckedIcon,

widget/material/editor.go

@@ -9,11 +9,13 @@ import (
 	"gioui.org/op"
 	"gioui.org/op/paint"
 	"gioui.org/text"
+	"gioui.org/unit"
 	"gioui.org/widget"
 )
 
 type Editor struct {
-	Font text.Font
+	Font     text.Font
+	TextSize unit.Value
 	// Color is the text color.
 	Color color.RGBA
 	// Hint contains the text displayed when the editor is empty.
@@ -26,9 +28,7 @@ type Editor struct {
 
 func (t *Theme) Editor(hint string) Editor {
 	return Editor{
-		Font: text.Font{
-			Size: t.TextSize,
-		},
+		TextSize:  t.TextSize,
 		Color:     t.Color.Text,
 		shaper:    t.Shaper,
 		Hint:      hint,
@@ -43,7 +43,7 @@ func (e Editor) Layout(gtx *layout.Context, editor *widget.Editor) {
 	macro.Record(gtx.Ops)
 	paint.ColorOp{Color: e.HintColor}.Add(gtx.Ops)
 	tl := widget.Label{Alignment: editor.Alignment}
-	tl.Layout(gtx, e.shaper, e.Font, e.Hint)
+	tl.Layout(gtx, e.shaper, e.Font, e.TextSize, e.Hint)
 	macro.Stop()
 	if w := gtx.Dimensions.Size.X; gtx.Constraints.Width.Min < w {
 		gtx.Constraints.Width.Min = w
@@ -51,7 +51,7 @@ func (e Editor) Layout(gtx *layout.Context, editor *widget.Editor) {
 	if h := gtx.Dimensions.Size.Y; gtx.Constraints.Height.Min < h {
 		gtx.Constraints.Height.Min = h
 	}
-	editor.Layout(gtx, e.shaper, e.Font)
+	editor.Layout(gtx, e.shaper, e.Font, e.TextSize)
 	if editor.Len() > 0 {
 		paint.ColorOp{Color: e.Color}.Add(gtx.Ops)
 		editor.PaintText(gtx)

widget/material/label.go

@@ -22,6 +22,7 @@ type Label struct {
 	// MaxLines limits the number of lines. Zero means no limit.
 	MaxLines int
 	Text     string
+	TextSize unit.Value
 
 	shaper text.Shaper
 }
@@ -64,17 +65,15 @@ func (t *Theme) Caption(txt string) Label {
 
 func (t *Theme) Label(size unit.Value, txt string) Label {
 	return Label{
-		Text:  txt,
-		Color: t.Color.Text,
-		Font: text.Font{
-			Size: size,
-		},
-		shaper: t.Shaper,
+		Text:     txt,
+		Color:    t.Color.Text,
+		TextSize: size,
+		shaper:   t.Shaper,
 	}
 }
 
 func (l Label) Layout(gtx *layout.Context) {
 	paint.ColorOp{Color: l.Color}.Add(gtx.Ops)
 	tl := widget.Label{Alignment: l.Alignment, MaxLines: l.MaxLines}
-	tl.Layout(gtx, l.shaper, l.Font, l.Text)
+	tl.Layout(gtx, l.shaper, l.Font, l.TextSize, l.Text)
 }

widget/material/radiobutton.go

@@ -4,7 +4,6 @@ package material
 
 import (
 	"gioui.org/layout"
-	"gioui.org/text"
 	"gioui.org/unit"
 	"gioui.org/widget"
 )
@@ -21,11 +20,9 @@ func (t *Theme) RadioButton(key, label string) RadioButton {
 		checkable: checkable{
 			Label: label,
 
-			Color:     t.Color.Text,
-			IconColor: t.Color.Primary,
-			Font: text.Font{
-				Size: t.TextSize.Scale(14.0 / 16.0),
-			},
+			Color:              t.Color.Text,
+			IconColor:          t.Color.Primary,
+			TextSize:           t.TextSize.Scale(14.0 / 16.0),
 			Size:               unit.Dp(26),
 			shaper:             t.Shaper,
 			checkedStateIcon:   t.radioCheckedIcon,