widget{,/material}: surface line height manipulation

This commit surfaces fields to manipulate the line height of all label and editor
types. It's unfortunate how this spreads through the API, but I don't see a good
way to eliminate that right now.

Signed-off-by: Chris Waldon <christopher.waldon.dev@gmail.com>

widget/editor.go

@@ -35,6 +35,12 @@ type Editor struct {
 	text textView
 	// Alignment controls the alignment of text within the editor.
 	Alignment text.Alignment
+	// LineHeight determines the gap between baselines of text. If zero, a sensible
+	// default will be used.
+	LineHeight unit.Sp
+	// LineHeightScale is multiplied by LineHeight to determine the final gap
+	// between baselines. If zero, a sensible default will be used.
+	LineHeightScale float32
 	// SingleLine force the text to stay on a single line.
 	// SingleLine also sets the scrolling direction to
 	// horizontal.
@@ -504,6 +510,8 @@ func (e *Editor) initBuffer() {
 		e.text.SetSource(e.buffer)
 	}
 	e.text.Alignment = e.Alignment
+	e.text.LineHeight = e.LineHeight
+	e.text.LineHeightScale = e.LineHeightScale
 	e.text.SingleLine = e.SingleLine
 	e.text.Mask = e.Mask
 	e.text.WrapPolicy = e.WrapPolicy

widget/label.go

@@ -30,6 +30,12 @@ type Label struct {
 	Truncator string
 	// WrapPolicy configures how displayed text will be broken into lines.
 	WrapPolicy text.WrapPolicy
+	// LineHeight controls the distance between the baselines of lines of text.
+	// If zero, a sensible default will be used.
+	LineHeight unit.Sp
+	// LineHeightScale applies a scaling factor to the LineHeight. If zero, a
+	// sensible default will be used.
+	LineHeightScale float32
 }
 
 // Layout the label with the given shaper, font, size, text, and material.
@@ -49,16 +55,19 @@ type TextInfo struct {
 func (l Label) LayoutDetailed(gtx layout.Context, lt *text.Shaper, font font.Font, size unit.Sp, txt string, textMaterial op.CallOp) (layout.Dimensions, TextInfo) {
 	cs := gtx.Constraints
 	textSize := fixed.I(gtx.Sp(size))
+	lineHeight := fixed.I(gtx.Sp(l.LineHeight))
 	lt.LayoutString(text.Parameters{
-		Font:       font,
+		Font:            font,
-		PxPerEm:    textSize,
+		PxPerEm:         textSize,
-		MaxLines:   l.MaxLines,
+		MaxLines:        l.MaxLines,
-		Truncator:  l.Truncator,
+		Truncator:       l.Truncator,
-		Alignment:  l.Alignment,
+		Alignment:       l.Alignment,
-		WrapPolicy: l.WrapPolicy,
+		WrapPolicy:      l.WrapPolicy,
-		MaxWidth:   cs.Max.X,
+		MaxWidth:        cs.Max.X,
-		MinWidth:   cs.Min.X,
+		MinWidth:        cs.Min.X,
-		Locale:     gtx.Locale,
+		Locale:          gtx.Locale,
+		LineHeight:      lineHeight,
+		LineHeightScale: l.LineHeightScale,
 	}, txt)
 	m := op.Record(gtx.Ops)
 	viewport := image.Rectangle{Max: cs.Max}

widget/material/editor.go

@@ -16,8 +16,14 @@ import (
 )
 
 type EditorStyle struct {
-	Font     font.Font
+	Font font.Font
-	TextSize unit.Sp
+	// LineHeight controls the distance between the baselines of lines of text.
+	// If zero, a sensible default will be used.
+	LineHeight unit.Sp
+	// LineHeightScale applies a scaling factor to the LineHeight. If zero, a
+	// sensible default will be used.
+	LineHeightScale float32
+	TextSize        unit.Sp
 	// Color is the text color.
 	Color color.NRGBA
 	// Hint contains the text displayed when the editor is empty.
@@ -64,7 +70,12 @@ func (e EditorStyle) Layout(gtx layout.Context) layout.Dimensions {
 	}
 
 	macro := op.Record(gtx.Ops)
-	tl := widget.Label{Alignment: e.Editor.Alignment, MaxLines: maxlines}
+	tl := widget.Label{
+		Alignment:       e.Editor.Alignment,
+		MaxLines:        maxlines,
+		LineHeight:      e.LineHeight,
+		LineHeightScale: e.LineHeightScale,
+	}
 	dims := tl.Layout(gtx, e.shaper, e.Font, e.TextSize, e.Hint, hintColor)
 	call := macro.Stop()
 
@@ -74,6 +85,8 @@ func (e EditorStyle) Layout(gtx layout.Context) layout.Dimensions {
 	if h := dims.Size.Y; gtx.Constraints.Min.Y < h {
 		gtx.Constraints.Min.Y = h
 	}
+	e.Editor.LineHeight = e.LineHeight
+	e.Editor.LineHeightScale = e.LineHeightScale
 	dims = e.Editor.Layout(gtx, e.shaper, e.Font, e.TextSize, textColor, selectionColor)
 	if e.Editor.Len() == 0 {
 		call.Add(gtx.Ops)

widget/material/label.go

@@ -38,6 +38,12 @@ type LabelStyle struct {
 	Text string
 	// TextSize determines the size of the text glyphs.
 	TextSize unit.Sp
+	// LineHeight controls the distance between the baselines of lines of text.
+	// If zero, a sensible default will be used.
+	LineHeight unit.Sp
+	// LineHeightScale applies a scaling factor to the LineHeight. If zero, a
+	// sensible default will be used.
+	LineHeightScale float32
 
 	// Shaper is the text shaper used to display this labe. This field is automatically
 	// set using by all constructor functions. If constructing a LabelStyle literal, you
@@ -132,13 +138,17 @@ func (l LabelStyle) Layout(gtx layout.Context) layout.Dimensions {
 		l.State.MaxLines = l.MaxLines
 		l.State.Truncator = l.Truncator
 		l.State.WrapPolicy = l.WrapPolicy
+		l.State.LineHeight = l.LineHeight
+		l.State.LineHeightScale = l.LineHeightScale
 		return l.State.Layout(gtx, l.Shaper, l.Font, l.TextSize, textColor, selectColor)
 	}
 	tl := widget.Label{
-		Alignment:  l.Alignment,
+		Alignment:       l.Alignment,
-		MaxLines:   l.MaxLines,
+		MaxLines:        l.MaxLines,
-		Truncator:  l.Truncator,
+		Truncator:       l.Truncator,
-		WrapPolicy: l.WrapPolicy,
+		WrapPolicy:      l.WrapPolicy,
+		LineHeight:      l.LineHeight,
+		LineHeightScale: l.LineHeightScale,
 	}
 	return tl.Layout(gtx, l.Shaper, l.Font, l.TextSize, l.Text, textColor)
 }

widget/selectable.go

@@ -59,9 +59,15 @@ type Selectable struct {
 	// if text was cut off. Defaults to "…" if left empty.
 	Truncator string
 	// WrapPolicy configures how displayed text will be broken into lines.
-	WrapPolicy  text.WrapPolicy
+	WrapPolicy text.WrapPolicy
-	initialized bool
+	// LineHeight controls the distance between the baselines of lines of text.
-	source      stringSource
+	// If zero, a sensible default will be used.
+	LineHeight unit.Sp
+	// LineHeightScale applies a scaling factor to the LineHeight. If zero, a
+	// sensible default will be used.
+	LineHeightScale float32
+	initialized     bool
+	source          stringSource
 	// scratch is a buffer reused to efficiently read text out of the
 	// textView.
 	scratch      []byte
@@ -181,6 +187,8 @@ func (l *Selectable) Truncated() bool {
 // paint material for the text and selection rectangles, respectively.
 func (l *Selectable) Layout(gtx layout.Context, lt *text.Shaper, font font.Font, size unit.Sp, textMaterial, selectionMaterial op.CallOp) layout.Dimensions {
 	l.initialize()
+	l.text.LineHeight = l.LineHeight
+	l.text.LineHeightScale = l.LineHeightScale
 	l.text.Alignment = l.Alignment
 	l.text.MaxLines = l.MaxLines
 	l.text.Truncator = l.Truncator

widget/text.go

@@ -44,6 +44,12 @@ type textSource interface {
 // be scrolled, and for configuring and drawing text selection boxes.
 type textView struct {
 	Alignment text.Alignment
+	// LineHeight controls the distance between the baselines of lines of text.
+	// If zero, a sensible default will be used.
+	LineHeight unit.Sp
+	// LineHeightScale applies a scaling factor to the LineHeight. If zero, a
+	// sensible default will be used.
+	LineHeightScale float32
 	// SingleLine forces the text to stay on a single line.
 	// SingleLine also sets the scrolling direction to
 	// horizontal.
@@ -273,6 +279,14 @@ func (e *textView) Update(gtx layout.Context, lt *text.Shaper, font font.Font, s
 		e.params.WrapPolicy = e.WrapPolicy
 		e.invalidate()
 	}
+	if lh := fixed.I(gtx.Sp(e.LineHeight)); lh != e.params.LineHeight {
+		e.params.LineHeight = lh
+		e.invalidate()
+	}
+	if e.LineHeightScale != e.params.LineHeightScale {
+		e.params.LineHeightScale = e.LineHeightScale
+		e.invalidate()
+	}
 
 	e.makeValid()
 	if eventHandling != nil {