text: Add AppendGlyphs and Glyphs

Closes #1767
Closes #1871

examples/text/main.go

@@ -79,9 +79,14 @@ type Game struct {
 	counter        int
 	kanjiText      []rune
 	kanjiTextColor color.RGBA
+	glyphs         []text.Glyph
 }
 
 func (g *Game) Update() error {
+	// Initialize the glyphs for special (colorful) rendering.
+	if len(g.glyphs) == 0 {
+		g.glyphs = text.AppendGlyphs(g.glyphs, mplusNormalFont, sampleText)
+	}
 	return nil
 }
 
@@ -115,6 +120,33 @@ func (g *Game) Draw(screen *ebiten.Image) {
 		ebitenutil.DrawRect(screen, float64(b.Min.X+x), float64(b.Min.Y+y), float64(b.Dx()), float64(b.Dy()), gray)
 		text.Draw(screen, sampleText, text.FaceWithLineHeight(mplusBigFont, lineHeight), x, y, color.White)
 	}
+	{
+		const x, y = 240, 400
+		op := &ebiten.DrawImageOptions{}
+		// g.glyphs is initialized by text.AppendGlyphs.
+		// You can customize how to render each glyph.
+		// In this example, multiple colors are used to render glyphs.
+		for i, gl := range g.glyphs {
+			op.GeoM.Reset()
+			op.GeoM.Translate(x, y)
+			op.GeoM.Translate(gl.X, gl.Y)
+			op.ColorM.Reset()
+			r := 1.0
+			if i%3 == 0 {
+				r = 0.5
+			}
+			g := 1.0
+			if i%3 == 1 {
+				g = 0.5
+			}
+			b := 1.0
+			if i%3 == 2 {
+				b = 0.5
+			}
+			op.ColorM.Scale(r, g, b, 1)
+			screen.DrawImage(gl.Image, op)
+		}
+	}
 }
 
 func (g *Game) Layout(outsideWidth, outsideHeight int) (int, int) {

text/text.go

@@ -392,3 +392,62 @@ func (f faceWithLineHeight) Metrics() font.Metrics {
 	m.Height = f.lineHeight
 	return m
 }
+
+// Glyphs is infomation to render one glyph.
+type Glyph struct {
+	// Rune is a character for this glyph.
+	Rune rune
+
+	// Image is an image for this glyph.
+	// Image is a grayscale image i.e. RGBA values are the same.
+	Image *ebiten.Image
+
+	// X is the X position to render this glyph.
+	// The position is determined in a sequence of characters given at AppendGlyphs.
+	// The position's origin is the first character's dot ('.') position.
+	X float64
+
+	// Y is the Y position to render this glyph.
+	// The position is determined in a sequence of characters given at AppendGlyphs.
+	// The position's origin is the first character's dot ('.') position.
+	Y float64
+}
+
+// AppendGlyphs appends the glyph information to glyphs.
+// You can render each glyphs as you like. See examples/text for an example of AppendGlyphs.
+func AppendGlyphs(glyphs []Glyph, face font.Face, text string) []Glyph {
+	textM.Lock()
+	defer textM.Unlock()
+
+	var pos fixed.Point26_6
+	prevR := rune(-1)
+
+	faceHeight := face.Metrics().Height
+
+	for _, r := range text {
+		if prevR >= 0 {
+			pos.X += face.Kern(prevR, r)
+		}
+		if r == '\n' {
+			pos.X = 0
+			pos.Y += faceHeight
+			prevR = rune(-1)
+			continue
+		}
+
+		if img := getGlyphImage(face, r); img != nil {
+			b := getGlyphBounds(face, r)
+			glyphs = append(glyphs, Glyph{
+				Rune:  r,
+				Image: img,
+				X:     math.Floor(fixed26_6ToFloat64(pos.X + b.Min.X)),
+				Y:     math.Floor(fixed26_6ToFloat64(pos.Y + b.Min.Y)),
+			})
+		}
+		pos.X += glyphAdvance(face, r)
+
+		prevR = r
+	}
+
+	return glyphs
+}