go.*,text,widget{,/material}: enable configurable line wrapping within words

This commit enables consumers of the text shaper to select a policy for how
line breaking candidates will be chosen. The new default policy can break lines
within "words" (UAX#14 segments) when words do not fit by themselves on a line.
This ensures that text does not horizontally overflow its bounding box unless
the available width is insufficient to display a single UAX#29 grapheme cluster.

Fixes: https://todo.sr.ht/~eliasnaur/gio/467
Signed-off-by: Chris Waldon <christopher.waldon.dev@gmail.com>

go.mod

@@ -6,7 +6,7 @@ require (
 	eliasnaur.com/font v0.0.0-20230308162249-dd43949cb42d
 	gioui.org/cpu v0.0.0-20210817075930-8d6a761490d2
 	gioui.org/shader v1.0.6
-	github.com/go-text/typesetting v0.0.0-20230413204129-b4f0492bf7ae
+	github.com/go-text/typesetting v0.0.0-20230602202114-9797aefac433
 	golang.org/x/exp v0.0.0-20221012211006-4de253d81b95
 	golang.org/x/exp/shiny v0.0.0-20220827204233-334a2380cb91
 	golang.org/x/image v0.5.0

go.sum

@@ -5,8 +5,8 @@ gioui.org/cpu v0.0.0-20210817075930-8d6a761490d2 h1:AGDDxsJE1RpcXTAxPG2B4jrwVUJG
 gioui.org/cpu v0.0.0-20210817075930-8d6a761490d2/go.mod h1:A8M0Cn5o+vY5LTMlnRoK3O5kG+rH0kWfJjeKd9QpBmQ=
 gioui.org/shader v1.0.6 h1:cvZmU+eODFR2545X+/8XucgZdTtEjR3QWW6W65b0q5Y=
 gioui.org/shader v1.0.6/go.mod h1:mWdiME581d/kV7/iEhLmUgUK5iZ09XR5XpduXzbePVM=
-github.com/go-text/typesetting v0.0.0-20230413204129-b4f0492bf7ae h1:LCcaQgYrnS+sx9Tc3oGUvbRBRt+5oFnKWakaxeAvNVI=
-github.com/go-text/typesetting v0.0.0-20230413204129-b4f0492bf7ae/go.mod h1:KmrpWuSMFcO2yjmyhGpnBGQHSKAoEgMTSSzvLDzCuEA=
+github.com/go-text/typesetting v0.0.0-20230602202114-9797aefac433 h1:Pdyvqsfi1QYgFfZa4R8otBOtgO+CGyBDMEG8cM3jwvE=
+github.com/go-text/typesetting v0.0.0-20230602202114-9797aefac433/go.mod h1:KmrpWuSMFcO2yjmyhGpnBGQHSKAoEgMTSSzvLDzCuEA=
 github.com/go-text/typesetting-utils v0.0.0-20230412163830-89e4bcfa3ecc h1:9Kf84pnrmmjdRzZIkomfjowmGUhHs20jkrWYw/I6CYc=
 github.com/yuin/goldmark v1.4.13/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=

text/gotext.go

@@ -401,11 +401,23 @@ func (s *shaperImpl) shapeText(faces []font.Face, ppem fixed.Int26_6, lc system.
 	return s.outScratchBuf
 }
 
+func wrapPolicyToGoText(p WrapPolicy) shaping.LineBreakPolicy {
+	switch p {
+	case WrapGraphemes:
+		return shaping.Always
+	case WrapWords:
+		return shaping.Never
+	default:
+		return shaping.WhenNecessary
+	}
+}
+
 // shapeAndWrapText invokes the text shaper and returns wrapped lines in the shaper's native format.
 func (s *shaperImpl) shapeAndWrapText(faces []font.Face, params Parameters, txt []rune) (_ []shaping.Line, truncated int) {
 	wc := shaping.WrapConfig{
 		TruncateAfterLines: params.MaxLines,
 		TextContinues:      params.forceTruncate,
+		BreakPolicy:        wrapPolicyToGoText(params.WrapPolicy),
 	}
 	if wc.TruncateAfterLines > 0 {
 		if len(params.Truncator) == 0 {
@@ -416,7 +428,7 @@ func (s *shaperImpl) shapeAndWrapText(faces []font.Face, params Parameters, txt
 		wc.Truncator = s.shapeText(faces, params.PxPerEm, params.Locale, []rune(params.Truncator))[0]
 	}
 	// Wrap outputs into lines.
-	return s.wrapper.WrapParagraph(wc, params.MaxWidth, txt, s.shapeText(faces, params.PxPerEm, params.Locale, txt)...)
+	return s.wrapper.WrapParagraph(wc, params.MaxWidth, txt, shaping.NewSliceIterator(s.shapeText(faces, params.PxPerEm, params.Locale, txt)))
 }
 
 // replaceControlCharacters replaces problematic unicode

text/gotext_test.go

@@ -10,6 +10,7 @@ import (
 	nsareg "eliasnaur.com/font/noto/sans/arabic/regular"
 	"github.com/go-text/typesetting/font"
 	"github.com/go-text/typesetting/shaping"
+	"golang.org/x/exp/slices"
 	"golang.org/x/image/font/gofont/goregular"
 	"golang.org/x/image/math/fixed"
 
@@ -235,6 +236,21 @@ func complexGlyph(cluster, runes, glyphs int) shaping.Glyph {
 	}
 }
 
+// copyLines performs a deep copy of the provided lines. This is necessary if you
+// want to use the line wrapper again while also using the lines.
+func copyLines(lines []shaping.Line) []shaping.Line {
+	out := make([]shaping.Line, len(lines))
+	for lineIdx, line := range lines {
+		lineCopy := make([]shaping.Output, len(line))
+		for runIdx, run := range line {
+			lineCopy[runIdx] = run
+			lineCopy[runIdx].Glyphs = slices.Clone(run.Glyphs)
+		}
+		out[lineIdx] = lineCopy
+	}
+	return out
+}
+
 // makeTestText creates a simple and complex(bidi) sample of shaped text at the given
 // font size and wrapped to the given line width. The runeLimit, if nonzero,
 // truncates the sample text to ensure shorter output for expensive tests.
@@ -277,11 +293,13 @@ func makeTestText(shaper *shaperImpl, primaryDir system.TextDirection, fontSize,
 		MaxWidth: lineWidth,
 		Locale:   locale,
 	}, []rune(simpleSource))
+	simpleText = copyLines(simpleText)
 	complexText, _ := shaper.shapeAndWrapText(shaper.orderer.sortedFacesForStyle(giofont.Font{}), Parameters{
 		PxPerEm:  fixed.I(fontSize),
 		MaxWidth: lineWidth,
 		Locale:   locale,
 	}, []rune(complexSource))
+	complexText = copyLines(complexText)
 	testShaper(rtlFace, ltrFace)
 	return simpleText, complexText
 }

text/lru.go

@@ -159,6 +159,7 @@ type layoutKey struct {
 	locale             system.Locale
 	font               giofont.Font
 	forceTruncate      bool
+	wrapPolicy         WrapPolicy
 }
 
 type pathKey struct {

text/shaper.go

@@ -16,6 +16,27 @@ import (
 	"golang.org/x/image/math/fixed"
 )
 
+// WrapPolicy configures strategies for choosing where to break lines of text for line
+// wrapping.
+type WrapPolicy uint8
+
+const (
+	// WrapHeuristically tries to minimize breaking within words (UAX#14 text segments)
+	// while also ensuring that text fits within the given MaxWidth. It will only break
+	// a line within a word (on a UAX#29 grapheme cluster boundary) when that word cannot
+	// fit on a line by itself. Additionally, when the final word of a line is being
+	// truncated, this policy will preserve as many symbols of that word as
+	// possible before the truncator.
+	WrapHeuristically WrapPolicy = iota
+	// WrapWords does not permit words (UAX#14 text segments) to be broken across lines.
+	// This means that sometimes long words will exceed the MaxWidth they are wrapped with.
+	WrapWords
+	// WrapGraphemes will maximize the amount of text on each line at the expense of readability,
+	// breaking any word across lines on UAX#29 grapheme cluster boundaries to maximize the number of
+	// grapheme clusters on each line.
+	WrapGraphemes
+)
+
 // Parameters are static text shaping attributes applied to the entire shaped text.
 type Parameters struct {
 	// Font describes the preferred typeface.
@@ -32,6 +53,9 @@ type Parameters struct {
 	// truncated.
 	Truncator string
 
+	// WrapPolicy configures how line breaks will be chosen when wrapping text across lines.
+	WrapPolicy WrapPolicy
+
 	// MinWidth and MaxWidth provide the minimum and maximum horizontal space constraints
 	// for the shaped text.
 	MinWidth, MaxWidth int
@@ -318,6 +342,7 @@ func (l *Shaper) layoutParagraph(params Parameters, asStr string, asBytes []byte
 		locale:        params.Locale,
 		font:          params.Font,
 		forceTruncate: params.forceTruncate,
+		wrapPolicy:    params.WrapPolicy,
 		str:           asStr,
 	}
 	if l, ok := l.layoutCache.Get(lk); ok {

widget/editor.go

@@ -57,6 +57,8 @@ type Editor struct {
 	// Filter is the list of characters allowed in the Editor. If Filter is empty,
 	// all characters are allowed.
 	Filter string
+	// WrapPolicy configures how displayed text will be broken into lines.
+	WrapPolicy text.WrapPolicy
 
 	buffer *editBuffer
 	// scratch is a byte buffer that is reused to efficiently read portions of text
@@ -504,6 +506,7 @@ func (e *Editor) initBuffer() {
 	e.text.Alignment = e.Alignment
 	e.text.SingleLine = e.SingleLine
 	e.text.Mask = e.Mask
+	e.text.WrapPolicy = e.WrapPolicy
 }
 
 // Layout lays out the editor using the provided textMaterial as the paint material

widget/editor_test.go

@@ -409,6 +409,7 @@ func TestEditorRTL(t *testing.T) {
 
 func TestEditorLigature(t *testing.T) {
 	e := new(Editor)
+	e.WrapPolicy = text.WrapWords
 	gtx := layout.Context{
 		Ops:         new(op.Ops),
 		Constraints: layout.Exact(image.Pt(100, 100)),

widget/label.go

@@ -28,6 +28,8 @@ type Label struct {
 	// Truncator is the text that will be shown at the end of the final
 	// line if MaxLines is exceeded. Defaults to "…" if empty.
 	Truncator string
+	// WrapPolicy configures how displayed text will be broken into lines.
+	WrapPolicy text.WrapPolicy
 }
 
 // Layout the label with the given shaper, font, size, text, and material.
@@ -35,14 +37,15 @@ func (l Label) Layout(gtx layout.Context, lt *text.Shaper, font font.Font, size
 	cs := gtx.Constraints
 	textSize := fixed.I(gtx.Sp(size))
 	lt.LayoutString(text.Parameters{
-		Font:      font,
-		PxPerEm:   textSize,
-		MaxLines:  l.MaxLines,
-		Truncator: l.Truncator,
-		Alignment: l.Alignment,
-		MaxWidth:  cs.Max.X,
-		MinWidth:  cs.Min.X,
-		Locale:    gtx.Locale,
+		Font:       font,
+		PxPerEm:    textSize,
+		MaxLines:   l.MaxLines,
+		Truncator:  l.Truncator,
+		Alignment:  l.Alignment,
+		WrapPolicy: l.WrapPolicy,
+		MaxWidth:   cs.Max.X,
+		MinWidth:   cs.Min.X,
+		Locale:     gtx.Locale,
 	}, txt)
 	m := op.Record(gtx.Ops)
 	viewport := image.Rectangle{Max: cs.Max}

widget/material/label.go

@@ -29,6 +29,8 @@ type LabelStyle struct {
 	Alignment text.Alignment
 	// MaxLines limits the number of lines. Zero means no limit.
 	MaxLines int
+	// WrapPolicy configures how displayed text will be broken into lines.
+	WrapPolicy text.WrapPolicy
 	// Truncator is the text that will be shown at the end of the final
 	// line if MaxLines is exceeded. Defaults to "…" if empty.
 	Truncator string
@@ -127,12 +129,14 @@ func (l LabelStyle) Layout(gtx layout.Context) layout.Dimensions {
 		l.State.Alignment = l.Alignment
 		l.State.MaxLines = l.MaxLines
 		l.State.Truncator = l.Truncator
+		l.State.WrapPolicy = l.WrapPolicy
 		return l.State.Layout(gtx, l.Shaper, l.Font, l.TextSize, textColor, selectColor)
 	}
 	tl := widget.Label{
-		Alignment: l.Alignment,
-		MaxLines:  l.MaxLines,
-		Truncator: l.Truncator,
+		Alignment:  l.Alignment,
+		MaxLines:   l.MaxLines,
+		Truncator:  l.Truncator,
+		WrapPolicy: l.WrapPolicy,
 	}
 	return tl.Layout(gtx, l.Shaper, l.Font, l.TextSize, l.Text, textColor)
 }

widget/selectable.go

@@ -57,7 +57,9 @@ type Selectable struct {
 	MaxLines int
 	// Truncator is the symbol to use at the end of the final line of text
 	// if text was cut off. Defaults to "…" if left empty.
-	Truncator   string
+	Truncator string
+	// WrapPolicy configures how displayed text will be broken into lines.
+	WrapPolicy  text.WrapPolicy
 	initialized bool
 	source      stringSource
 	// scratch is a buffer reused to efficiently read text out of the
@@ -182,6 +184,7 @@ func (l *Selectable) Layout(gtx layout.Context, lt *text.Shaper, font font.Font,
 	l.text.Alignment = l.Alignment
 	l.text.MaxLines = l.MaxLines
 	l.text.Truncator = l.Truncator
+	l.text.WrapPolicy = l.WrapPolicy
 	l.text.Update(gtx, lt, font, size, l.handleEvents)
 	dims := l.text.Dimensions()
 	defer clip.Rect(image.Rectangle{Max: dims.Size}).Push(gtx.Ops).Pop()

widget/text.go

@@ -53,6 +53,8 @@ type textView struct {
 	// Truncator is the text that will be shown at the end of the final
 	// line if MaxLines is exceeded. Defaults to "…" if empty.
 	Truncator string
+	// WrapPolicy configures how displayed text will be broken into lines.
+	WrapPolicy text.WrapPolicy
 	// Mask replaces the visual display of each rune in the contents with the given rune.
 	// Newline characters are not masked. When non-zero, the unmasked contents
 	// are accessed by Len, Text, and SetText.
@@ -267,6 +269,10 @@ func (e *textView) Update(gtx layout.Context, lt *text.Shaper, font font.Font, s
 		e.params.MaxLines = e.MaxLines
 		e.invalidate()
 	}
+	if e.WrapPolicy != e.params.WrapPolicy {
+		e.params.WrapPolicy = e.WrapPolicy
+		e.invalidate()
+	}
 
 	e.makeValid()
 	if eventHandling != nil {