text/v2: bug fix: correct rendering vertical texts in Mongolian

Closes #2849
Updates go-text/typesetting#111

examples/texti18n/LICENSE.md

@@ -16,6 +16,12 @@ Open Font License 1.1
 
 https://fonts.google.com/noto/specimen/Noto+Sans+Myanmar/about
 
+# `NotoSansMongolian-Regular.ttf`
+
+Open Font License 1.1
+
+https://fonts.google.com/noto/specimen/Noto+Sans+Mongolian/about
+
 # `NotoSansThai-Regular.ttf`
 
 Open Font License 1.1

examples/texti18n/main.go

@@ -83,6 +83,19 @@ func init() {
 	myanmarFaceSource = s
 }
 
+//go:embed NotoSansMongolian-Regular.ttf
+var mongolianTTF []byte
+
+var mongolianFaceSource *text.GoTextFaceSource
+
+func init() {
+	s, err := text.NewGoTextFaceSource(bytes.NewReader(mongolianTTF))
+	if err != nil {
+		log.Fatal(err)
+	}
+	mongolianFaceSource = s
+}
+
 var japaneseFaceSource *text.GoTextFaceSource
 
 func init() {
@@ -167,7 +180,26 @@ func (g *Game) Draw(screen *ebiten.Image) {
 		text.Draw(screen, thaiText, f, op)
 	}
 	{
-		const japaneseText = "あのイーハトーヴォの\nすきとおった風、\n夏でも底に冷たさを\nもつ青いそら…"
+		const mongolianText = "ᠬᠦᠮᠦᠨ ᠪᠦᠷ ᠲᠥᠷᠥᠵᠦ ᠮᠡᠨᠳᠡᠯᠡᠬᠦ\nᠡᠷᠬᠡ ᠴᠢᠯᠥᠭᠡ ᠲᠡᠢ᠂ ᠠᠳᠠᠯᠢᠬᠠᠨ"
+		f := &text.GoTextFace{
+			Source:    mongolianFaceSource,
+			Direction: text.DirectionTopToBottomAndLeftToRight,
+			Size:      24,
+			Language:  language.Mongolian,
+			// language.Mongolian.Script() returns "Cyrl" (Cyrillic), but we want Mongolian script here.
+			Script: language.MustParseScript("Mong"),
+		}
+		const lineSpacing = 48
+		x, y := 20, 280
+		w, h := text.Measure(mongolianText, f, lineSpacing)
+		vector.DrawFilledRect(screen, float32(x), float32(y), float32(w), float32(h), gray, false)
+		op := &text.DrawOptions{}
+		op.GeoM.Translate(float64(x), float64(y))
+		op.LineSpacingInPixels = lineSpacing
+		text.Draw(screen, mongolianText, f, op)
+	}
+	{
+		const japaneseText = "あのイーハトーヴォの\nすきとおった風、\n夏でも底に冷たさを\nもつ青いそら…\nあHello World.あ"
 		f := &text.GoTextFace{
 			Source:    japaneseFaceSource,
 			Direction: text.DirectionTopToBottomAndRightToLeft,

go.mod

@@ -5,7 +5,7 @@ go 1.18
 require (
 	github.com/ebitengine/oto/v3 v3.2.0-alpha.2.0.20231021101548-b794c0292b2b
 	github.com/ebitengine/purego v0.6.0-alpha.2
-	github.com/go-text/typesetting v0.0.0-20231211160022-6295f3c76f4d
+	github.com/go-text/typesetting v0.0.0-20231221124458-48cc05a56658
 	github.com/hajimehoshi/bitmapfont/v3 v3.0.0
 	github.com/hajimehoshi/go-mp3 v0.3.4
 	github.com/jakecoffman/cp v1.2.1

go.sum

@@ -2,9 +2,9 @@ github.com/ebitengine/oto/v3 v3.2.0-alpha.2.0.20231021101548-b794c0292b2b h1:gi7
 github.com/ebitengine/oto/v3 v3.2.0-alpha.2.0.20231021101548-b794c0292b2b/go.mod h1:JtMbxJHZBDXfS8BmVYwzWk9Z6r7jsjwsHzOuZrEkfs4=
 github.com/ebitengine/purego v0.6.0-alpha.2 h1:lYSvMtNBEjNGAzqPC5WP7bHUOxkFU3L+JZMdxK7krkw=
 github.com/ebitengine/purego v0.6.0-alpha.2/go.mod h1:ah1In8AOtksoNK6yk5z1HTJeUkC1Ez4Wk2idgGslMwQ=
-github.com/go-text/typesetting v0.0.0-20231211160022-6295f3c76f4d h1:AFVBrIZZMhmnB8NbkKayNVz714G048XqZGmNhXjvSag=
+github.com/go-text/typesetting v0.0.0-20231221124458-48cc05a56658 h1:KeDKnC99J3l5qJK4zV13Au2UwPn4N20TnIlM0YvILj8=
-github.com/go-text/typesetting v0.0.0-20231211160022-6295f3c76f4d/go.mod h1:MrLApvxyzSW0MhQqLc484jkUWYX4wsEvEqDosB5Io80=
+github.com/go-text/typesetting v0.0.0-20231221124458-48cc05a56658/go.mod h1:d22AnmeKq/on0HNv73UFriMKc4Ez6EqZAofLhAzpSzI=
-github.com/go-text/typesetting-utils v0.0.0-20231204162240-fa4dc564ba79 h1:3yBOzx29wog0i7TnUBMcp90EwIb+A5kqmr5vny1UOm8=
+github.com/go-text/typesetting-utils v0.0.0-20231211103740-d9332ae51f04 h1:zBx+p/W2aQYtNuyZNcTfinWvXBQwYtDfme051PR/lAY=
 github.com/hajimehoshi/bitmapfont/v3 v3.0.0 h1:r2+6gYK38nfztS/et50gHAswb9hXgxXECYgE8Nczmi4=
 github.com/hajimehoshi/bitmapfont/v3 v3.0.0/go.mod h1:+CxxG+uMmgU4mI2poq944i3uZ6UYFfAkj9V6WqmuvZA=
 github.com/hajimehoshi/go-mp3 v0.3.4 h1:NUP7pBYH8OguP4diaTZ9wJbUbk3tC0KlfzsEpWmYj68=

text/v2/gotext.go

@@ -278,11 +278,17 @@ func (g *GoTextFace) gScript() glanguage.Script {
 
 // advance implements Face.
 func (g *GoTextFace) advance(text string) float64 {
-	output, _ := g.Source.shape(text, g)
+	outputs, _ := g.Source.shape(text, g)
-	if g.direction().isHorizontal() {
+
-		return fixed26_6ToFloat64(output.Advance)
+	var a fixed.Int26_6
+	for _, output := range outputs {
+		a += output.Advance
 	}
-	return -fixed26_6ToFloat64(output.Advance)
+
+	if g.direction().isHorizontal() {
+		return fixed26_6ToFloat64(a)
+	}
+	return -fixed26_6ToFloat64(a)
 }
 
 // hasGlyph implements Face.

text/v2/gotextfacesource.go

@@ -49,7 +49,7 @@ type glyph struct {
 }
 
 type goTextOutputCacheValue struct {
-	output shaping.Output
+	outputs []shaping.Output
 	glyphs  []glyph
 	atime   int64
 }
@@ -164,7 +164,7 @@ func (g *GoTextFaceSource) UnsafeInternal() font.Face {
 	return g.f
 }
 
-func (g *GoTextFaceSource) shape(text string, face *GoTextFace) (shaping.Output, []glyph) {
+func (g *GoTextFaceSource) shape(text string, face *GoTextFace) ([]shaping.Output, []glyph) {
 	g.copyCheck()
 
 	g.m.Lock()
@@ -173,7 +173,7 @@ func (g *GoTextFaceSource) shape(text string, face *GoTextFace) (shaping.Output,
 	key := face.outputCacheKey(text)
 	if out, ok := g.outputCache[key]; ok {
 		out.atime = now()
-		return out.output, out.glyphs
+		return out.outputs, out.glyphs
 	}
 
 	g.f.SetVariations(face.variations)
@@ -189,23 +189,45 @@ func (g *GoTextFaceSource) shape(text string, face *GoTextFace) (shaping.Output,
 		Script:       face.gScript(),
 		Language:     language.Language(face.Language.String()),
 	}
-	out := (&shaping.HarfbuzzShaper{}).Shape(input)
+
-	if g.outputCache == nil {
+	var inputs []shaping.Input
-		g.outputCache = map[goTextOutputCacheKey]*goTextOutputCacheValue{}
+	if face.Direction.isHorizontal() {
+		// shaping.Segmenter is not used for horizontal texts so far due to a bug (go-text/typesetting#127).
+		inputs = []shaping.Input{input}
+	} else {
+		var seg shaping.Segmenter
+		inputs = seg.Split(input, &singleFontmap{face: face.Source.f})
 	}
 
+	if face.Direction == DirectionRightToLeft {
+		// Reverse the input for RTL texts.
+		for i, j := 0, len(inputs)-1; i < j; i, j = i+1, j-1 {
+			inputs[i], inputs[j] = inputs[j], inputs[i]
+		}
+	}
+
+	outputs := make([]shaping.Output, len(inputs))
+	var gs []glyph
+	for i, input := range inputs {
+		out := (&shaping.HarfbuzzShaper{}).Shape(input)
+		outputs[i] = out
+
+		(shaping.Line{out}).AdjustBaselines()
+
 		var indices []int
 		for i := range text {
 			indices = append(indices, i)
 		}
 		indices = append(indices, len(text))
 
-	gs := make([]glyph, len(out.Glyphs))
+		for _, gl := range out.Glyphs {
-	for i, gl := range out.Glyphs {
 			gl := gl
 			var segs []api.Segment
 			switch data := g.f.GlyphData(gl.GlyphID).(type) {
 			case api.GlyphOutline:
+				if out.Direction.IsSideways() {
+					data.Sideways(fixed26_6ToFloat32(-gl.YOffset) / fixed26_6ToFloat32(out.Size) * float32(face.Source.f.Upem()))
+				}
 				segs = data.Segments
 			case api.GlyphSVG:
 				segs = data.Outline.Segments
@@ -225,16 +247,21 @@ func (g *GoTextFaceSource) shape(text string, face *GoTextFace) (shaping.Output,
 				}
 			}
 
-		gs[i] = glyph{
+			gs = append(gs, glyph{
 				shapingGlyph:   &gl,
 				startIndex:     indices[gl.ClusterIndex],
 				endIndex:       indices[gl.ClusterIndex+gl.RuneCount],
 				scaledSegments: scaledSegs,
 				bounds:         segmentsToBounds(scaledSegs),
+			})
 		}
 	}
+
+	if g.outputCache == nil {
+		g.outputCache = map[goTextOutputCacheKey]*goTextOutputCacheValue{}
+	}
 	g.outputCache[key] = &goTextOutputCacheValue{
-		output: out,
+		outputs: outputs,
 		glyphs:  gs,
 		atime:   now(),
 	}
@@ -250,7 +277,7 @@ func (g *GoTextFaceSource) shape(text string, face *GoTextFace) (shaping.Output,
 		}
 	}
 
-	return out, gs
+	return outputs, gs
 }
 
 func (g *GoTextFaceSource) scale(size float64) float64 {
@@ -266,3 +293,11 @@ func (g *GoTextFaceSource) getOrCreateGlyphImage(goTextFace *GoTextFace, key goT
 	}
 	return g.glyphImageCache[goTextFace.Size].getOrCreate(goTextFace, key, create)
 }
+
+type singleFontmap struct {
+	face font.Face
+}
+
+func (s *singleFontmap) ResolveFace(r rune) font.Face {
+	return s.face
+}

text/v2/layout.go

@@ -186,22 +186,18 @@ func forEachLine(text string, face Face, options *LayoutOptions, f func(text str
 		boundaryWidth = longestAdvance
 		boundaryHeight = float64(lineCount-1)*options.LineSpacingInPixels + m.HAscent + m.HDescent
 	} else {
+		// TODO: Perhaps HAscent and HDescent should be used for sideways glyphs.
 		boundaryWidth = float64(lineCount-1)*options.LineSpacingInPixels + m.VAscent + m.VDescent
 		boundaryHeight = longestAdvance
 	}
 
 	var offsetX, offsetY float64
 
-	// The Y position has an offset by an ascent for horizontal texts.
-	if d.isHorizontal() {
-		offsetY += m.HAscent
-	}
-	// TODO: Adjust offsets for vertical texts.
-
 	// Adjust the offset based on the secondary alignments.
 	h, v := calcAligns(d, options.PrimaryAlign, options.SecondaryAlign)
 	switch d {
 	case DirectionLeftToRight, DirectionRightToLeft:
+		offsetY += m.HAscent
 		switch v {
 		case verticalAlignTop:
 		case verticalAlignCenter:
@@ -210,7 +206,8 @@ func forEachLine(text string, face Face, options *LayoutOptions, f func(text str
 			offsetY -= boundaryHeight
 		}
 	case DirectionTopToBottomAndLeftToRight:
-		offsetX -= m.VAscent
+		// TODO: Perhaps HDescent should be used for sideways glyphs.
+		offsetX += m.VDescent
 		switch h {
 		case horizontalAlignLeft:
 		case horizontalAlignCenter:
@@ -219,6 +216,7 @@ func forEachLine(text string, face Face, options *LayoutOptions, f func(text str
 			offsetX -= boundaryWidth
 		}
 	case DirectionTopToBottomAndRightToLeft:
+		// TODO: Perhaps HAscent should be used for sideways glyphs.
 		offsetX -= m.VAscent
 		switch h {
 		case horizontalAlignLeft: