text: Unify draw calls for multiple runes (#535)

text/text.go

@@ -57,7 +57,11 @@ var (
 	colorMCache = map[colorMCacheKey]*colorMCacheEntry{}
 )
 
-func drawGlyph(dst *ebiten.Image, face font.Face, r rune, x, y fixed.Int26_6, clr color.Color) {
+func drawGlyph(dst *ebiten.Image, face font.Face, r rune, img *glyphImage, x, y fixed.Int26_6, clr color.Color) {
+	if img == nil {
+		return
+	}
+
 	// RGBA() is in [0 - 0xffff]. Adjust them in [0 - 0xff].
 	cr, cg, cb, ca := clr.RGBA()
 	cr >>= 8
@@ -68,11 +72,6 @@ func drawGlyph(dst *ebiten.Image, face font.Face, r rune, x, y fixed.Int26_6, cl
 		return
 	}
 
-	img := getGlyphImage(face, r)
-	if img == nil {
-		return
-	}
-
 	b := getGlyphBounds(face, r)
 	op := &ebiten.DrawImageOptions{}
 	op.GeoM.Translate(fixed26_6ToFloat64(x+b.Min.X), fixed26_6ToFloat64(y+b.Min.Y))
@@ -107,8 +106,10 @@ func drawGlyph(dst *ebiten.Image, face font.Face, r rune, x, y fixed.Int26_6, cl
 		colorMCache[key] = e
 	}
 	op.ColorM = e.m
+	re := image.Rect(img.x, img.y, img.x+img.width, img.y+img.height)
+	op.SourceRect = &re
 
-	_ = dst.DrawImage(img, op)
+	_ = dst.DrawImage(img.image, op)
 }
 
 var (
@@ -128,8 +129,16 @@ func getGlyphBounds(face font.Face, r rune) *fixed.Rectangle26_6 {
 	return &b
 }
 
-type glyphImageCacheEntry struct {
+type glyphImage struct {
 	image  *ebiten.Image
+	x      int
+	y      int
+	width  int
+	height int
+}
+
+type glyphImageCacheEntry struct {
+	image *glyphImage
 	atime int64
 }
 
@@ -138,7 +147,7 @@ var (
 	emptyGlyphs     = map[font.Face]map[rune]struct{}{}
 )
 
-func getGlyphImage(face font.Face, r rune) *ebiten.Image {
+func getGlyphImages(face font.Face, runes []rune) []*glyphImage {
 	if _, ok := emptyGlyphs[face]; !ok {
 		emptyGlyphs[face] = map[rune]struct{}{}
 	}
@@ -146,21 +155,27 @@ func getGlyphImage(face font.Face, r rune) *ebiten.Image {
 		glyphImageCache[face] = map[rune]*glyphImageCacheEntry{}
 	}
 
+	imgs := make([]*glyphImage, len(runes))
+	neededGlyphs := map[int]*fixed.Rectangle26_6{}
+	for i, r := range runes {
 		if _, ok := emptyGlyphs[face][r]; ok {
-		return nil
+			continue
 		}
+
 		if e, ok := glyphImageCache[face][r]; ok {
 			e.atime = now()
-		return e.image
+			imgs[i] = e.image
+			continue
 		}
 
 		b := getGlyphBounds(face, r)
 		w, h := (b.Max.X - b.Min.X).Ceil(), (b.Max.Y - b.Min.Y).Ceil()
 		if w == 0 || h == 0 {
 			emptyGlyphs[face][r] = struct{}{}
-		return nil
+			continue
 		}
 
+		// TODO: What if len(runes) > cacheLimit?
 		if len(glyphImageCache[face]) > cacheLimit {
 			oldest := int64(math.MaxInt64)
 			oldestKey := rune(-1)
@@ -170,25 +185,53 @@ func getGlyphImage(face font.Face, r rune) *ebiten.Image {
 					oldest = e.atime
 				}
 			}
-		glyphImageCache[face][oldestKey].image.Dispose()
 			delete(glyphImageCache[face], oldestKey)
 		}
 
-	rgba := image.NewRGBA(image.Rect(0, 0, w, h))
+		neededGlyphs[i] = b
+	}
+
+	w2 := 0
+	h2 := 0
+	for _, b := range neededGlyphs {
+		w, h := (b.Max.X - b.Min.X).Ceil(), (b.Max.Y - b.Min.Y).Ceil()
+		w2 += w
+		if h2 < h {
+			h2 = h
+		}
+	}
+	rgba := image.NewRGBA(image.Rect(0, 0, w2, h2))
+
+	x := 0
+	for i, b := range neededGlyphs {
+		w, h := (b.Max.X - b.Min.X).Ceil(), (b.Max.Y - b.Min.Y).Ceil()
+
+		r := runes[i]
 		d := font.Drawer{
 			Dst:  rgba,
 			Src:  image.White,
 			Face: face,
 		}
-	d.Dot = fixed.Point26_6{-b.Min.X, -b.Min.Y}
+		d.Dot = fixed.Point26_6{fixed.I(x) - b.Min.X, -b.Min.Y}
 		d.DrawString(string(r))
 
 		img, _ := ebiten.NewImageFromImage(rgba, ebiten.FilterDefault)
-	glyphImageCache[face][r] = &glyphImageCacheEntry{
+		g := &glyphImage{
 			image:  img,
+			x:      x,
+			y:      0,
+			width:  w,
+			height: h,
+		}
+		glyphImageCache[face][r] = &glyphImageCacheEntry{
+			image: g,
 			atime: now(),
 		}
-	return img
+		imgs[i] = g
+
+		x += w
+	}
+	return imgs
 }
 
 var textM sync.Mutex
@@ -214,11 +257,12 @@ func Draw(dst *ebiten.Image, text string, face font.Face, x, y int, clr color.Co
 	prevR := rune(-1)
 
 	runes := []rune(text)
-	for _, r := range runes {
+	glyphImgs := getGlyphImages(face, runes)
+	for i, r := range runes {
 		if prevR >= 0 {
 			fx += face.Kern(prevR, r)
 		}
-		drawGlyph(dst, face, r, fx, fixed.I(y), clr)
+		drawGlyph(dst, face, r, glyphImgs[i], fx, fixed.I(y), clr)
 		fx += glyphAdvance(face, r)
 
 		prevR = r