basicwidget: add ranged font size scales

Consume the last ranged style property: a run's scale override
multiplies the base font size for the run's face, flowing through the
existing face-run pipeline so wrapping, caret geometry, and hit-testing
pick up the scaled advances. The line height stays uniform — scaled
runs render on the line's shared baseline, and glyphs scaled past the
line height may overlap adjacent lines, matching how browsers lay out
mixed font sizes under a fixed line-height. The scale counts as a
metric-affecting property, and the core and basicwidget.Text expose
SetScaleInRange and UnsetScaleInRange.

Styled drawing now aligns each segment's baseline with the base face's
by shifting by the ascent difference, since text.Draw positions text by
its top. Previously segments were top-aligned, which was invisible
while all mixed faces shared the same ascent but misaligns faces with
different metrics, such as scaled runs or family overrides.

The gallery's Rich Texts sample gains light and scaled ranges, with the
sample reworded so the standalone "light" precedes "highlighted", whose
inner "light" substring the first-match range helper would style
otherwise.

Updates #131

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: hajimehoshi

basicwidget/internal/textstyle/statekey.go

@@ -57,7 +57,7 @@ func (r *Runs) HasMetricProperties() bool {
 // HasMetricProperties reports whether the style overrides a metric-affecting
 // property, such as a variation setting or the font family.
 func (s Style) HasMetricProperties() bool {
-	return len(s.variations) > 0 || len(s.features) > 0 || s.italic.set || s.family.set || s.lang.set
+	return len(s.variations) > 0 || len(s.features) > 0 || s.italic.set || s.family.set || s.lang.set || s.scale.set
 }
 
 // writeStateKey writes the style's consumed properties into w.
@@ -95,6 +95,11 @@ func (s Style) writeMetricProperties(w Writer) {
 	italic, ok := s.Italic()
 	w.WriteBool(ok)
 	w.WriteBool(italic)
+	scale, ok := s.Scale()
+	w.WriteBool(ok)
+	if ok {
+		w.WriteFloat64(scale)
+	}
 	lang, ok := s.Lang()
 	w.WriteBool(ok)
 	if ok {

basicwidget/internal/textstyle/style_test.go

@@ -60,6 +60,11 @@ func TestStyleHasMetricProperties(t *testing.T) {
 			style: textstyle.Style{}.WithLang(language.Japanese),
 			want:  true,
 		},
+		{
+			name:  "scale",
+			style: textstyle.Style{}.WithScale(1.5),
+			want:  true,
+		},
 	}
 
 	for _, tt := range tests {

basicwidget/internal/textutil/draw.go

@@ -460,6 +460,7 @@ func faceRunsIntersect(faceRuns []FaceRun, start, end int) bool {
 func drawStyledVisualLine(dst *ebiten.Image, vlStr string, lineStart, contentEnd int, runs []StyleRun, options *DrawOptions, op *text.DrawOptions) {
 	origGeoM := op.GeoM
 	origColorScale := op.ColorScale
+	baseAscent := options.Face.TextFace().Metrics().HAscent
 	var x float64
 	var i int
 	for i < len(vlStr) {
@@ -482,12 +483,16 @@ func drawStyledVisualLine(dst *ebiten.Image, vlStr string, lineStart, contentEnd
 		}
 		seg := vlStr[i:segEnd]
 		face := segFace.TextFace()
+		// text.Draw positions text by its top, so a face whose ascent
+		// differs from the base face's shifts by the difference to keep the
+		// baselines aligned.
+		dy := baseAscent - face.Metrics().HAscent
 		var chunkStart int
 		for chunkStart < len(seg) {
 			clr, colorChange := styleRunColorAt(runs, options.TextColor, contentEnd, lineStart+i+chunkStart)
 			chunkEnd := min(colorChange-lineStart-i, len(seg))
 			geoM := op.GeoM
-			op.GeoM.Translate(x+text.AdvanceAt(seg, chunkStart, face), 0)
+			op.GeoM.Translate(x+text.AdvanceAt(seg, chunkStart, face), dy)
 			op.ColorScale.Reset()
 			op.ColorScale.ScaleWithColor(clr)
 			text.Draw(dst, seg[chunkStart:chunkEnd], face, op)

basicwidget/internal/textwidget/style.go

@@ -224,6 +224,20 @@ func (t *Text) UnsetFontFamilyInRange(startInBytes, endInBytes int) {
 	t.ensureStyleRuns().UnsetFamily(startInBytes, endInBytes)
 }
 
+// SetScaleInRange overrides the font size in [startInBytes, endInBytes) as a
+// multiplier applied to the base font size. The override lasts until the
+// value changes. The line height is unaffected; the range renders on the
+// line's baseline.
+func (t *Text) SetScaleInRange(startInBytes, endInBytes int, scale float64) {
+	t.ensureStyleRuns().SetScale(startInBytes, endInBytes, scale)
+}
+
+// UnsetScaleInRange removes the font size override in
+// [startInBytes, endInBytes).
+func (t *Text) UnsetScaleInRange(startInBytes, endInBytes int) {
+	t.ensureStyleRuns().UnsetScale(startInBytes, endInBytes)
+}
+
 // SetLangInRange overrides the language used to select the face and its
 // features when shaping [startInBytes, endInBytes). The override lasts until
 // the value changes.
@@ -340,6 +354,9 @@ func (t *Text) appendFaceRunsForStyle(runs []textutil.FaceRun, context *guigui.C
 		if italic, ok := run.Style.Italic(); ok {
 			attrs.Italic = italic
 		}
+		if scale, ok := run.Style.Scale(); ok {
+			attrs.Size *= scale
+		}
 		if lang, ok := run.Style.Lang(); ok {
 			attrs.Lang = lang
 		}

basicwidget/text.go

@@ -447,6 +447,21 @@ func (t *Text) UnsetItalicInRange(startInBytes, endInBytes int) {
 	t.core.UnsetItalicInRange(startInBytes, endInBytes)
 }
 
+// SetScaleInRange overrides the font size in [startInBytes, endInBytes) as a
+// multiplier applied to the base font size. The override lasts until the
+// value changes. The line height is unaffected; the range renders on the
+// line's baseline, and glyphs scaled past the line height may overlap
+// adjacent lines.
+func (t *Text) SetScaleInRange(startInBytes, endInBytes int, scale float64) {
+	t.core.SetScaleInRange(startInBytes, endInBytes, scale)
+}
+
+// UnsetScaleInRange removes the font size override in
+// [startInBytes, endInBytes).
+func (t *Text) UnsetScaleInRange(startInBytes, endInBytes int) {
+	t.core.UnsetScaleInRange(startInBytes, endInBytes)
+}
+
 // SetLangInRange overrides the language used to select the face and its
 // features when shaping [startInBytes, endInBytes). The override lasts until
 // the value changes.

example/gallery/richtexts.go

@@ -14,7 +14,7 @@ import (
 	"github.com/guigui-gui/guigui/basicwidget"
 )
 
-const richTextsSampleText = "Colored, highlighted, underlined, struck-through, and bold ranges.\n" +
+const richTextsSampleText = "Colored, light, highlighted, underlined, struck-through, bold, and scaled ranges.\n" +
 	"Combined styles apply to a single range.\n" +
 	"A sufficiently long styled range continues across the visual line boundary when the text wraps, keeping its background and underline on every visual line it covers.\n" +
 	"日本語のテキストにも下線と背景を適用できます。"
@@ -86,6 +86,12 @@ func (r *RichTexts) Build(context *guigui.Context, adder *guigui.ChildAdder) err
 	styleRichTextsSampleRange("bold", func(start, end int) {
 		t.SetWeightInRange(start, end, text.WeightBold)
 	})
+	styleRichTextsSampleRange("light", func(start, end int) {
+		t.SetWeightInRange(start, end, text.WeightLight)
+	})
+	styleRichTextsSampleRange("scaled", func(start, end int) {
+		t.SetScaleInRange(start, end, 1.5)
+	})
 	styleRichTextsSampleRange("Combined styles", func(start, end int) {
 		t.SetColorInRange(start, end, blue)
 		t.SetBackgroundColorInRange(start, end, green)