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>

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 {