moved a freetype source file into the project and optimized it for the given purpose, only upload rendered text rectangle to the texture

freetype.go

@@ -0,0 +1,335 @@
+// Copyright 2010 The Freetype-Go Authors. All rights reserved.
+// Use of this source code is governed by your choice of either the
+// FreeType License or the GNU General Public License version 2 (or
+// any later version), both of which can be found in the LICENSE file.
+
+// The freetype package provides a convenient API to draw text onto an image.
+// Use the freetype/raster and freetype/truetype packages for lower level
+// control over rasterization and TrueType parsing.
+package canvas
+
+import (
+	"errors"
+	"image"
+	"image/draw"
+
+	"github.com/golang/freetype/raster"
+	"github.com/golang/freetype/truetype"
+	"golang.org/x/image/font"
+	"golang.org/x/image/math/fixed"
+)
+
+// These constants determine the size of the glyph cache. The cache is keyed
+// primarily by the glyph index modulo nGlyphs, and secondarily by sub-pixel
+// position for the mask image. Sub-pixel positions are quantized to
+// nXFractions possible values in both the x and y directions.
+const (
+	nGlyphs     = 256
+	nXFractions = 4
+	nYFractions = 1
+)
+
+// An entry in the glyph cache is keyed explicitly by the glyph index and
+// implicitly by the quantized x and y fractional offset. It maps to a mask
+// image and an offset.
+type cacheEntry struct {
+	valid        bool
+	glyph        truetype.Index
+	advanceWidth fixed.Int26_6
+	mask         *image.Alpha
+	offset       image.Point
+}
+
+// A Context holds the state for drawing text in a given font and size.
+type frContext struct {
+	r        *raster.Rasterizer
+	f        *truetype.Font
+	glyphBuf truetype.GlyphBuf
+	// clip is the clip rectangle for drawing.
+	clip image.Rectangle
+	// dst and src are the destination and source images for drawing.
+	dst draw.Image
+	src image.Image
+	// fontSize and dpi are used to calculate scale. scale is the number of
+	// 26.6 fixed point units in 1 em. hinting is the hinting policy.
+	fontSize, dpi float64
+	scale         fixed.Int26_6
+	hinting       font.Hinting
+	// cache is the glyph cache.
+	cache [nGlyphs * nXFractions * nYFractions]cacheEntry
+}
+
+// drawContour draws the given closed contour with the given offset.
+func (c *frContext) drawContour(ps []truetype.Point, dx, dy fixed.Int26_6) {
+	if len(ps) == 0 {
+		return
+	}
+
+	// The low bit of each point's Flags value is whether the point is on the
+	// curve. Truetype fonts only have quadratic Bézier curves, not cubics.
+	// Thus, two consecutive off-curve points imply an on-curve point in the
+	// middle of those two.
+	//
+	// See http://chanae.walon.org/pub/ttf/ttf_glyphs.htm for more details.
+
+	// ps[0] is a truetype.Point measured in FUnits and positive Y going
+	// upwards. start is the same thing measured in fixed point units and
+	// positive Y going downwards, and offset by (dx, dy).
+	start := fixed.Point26_6{
+		X: dx + ps[0].X,
+		Y: dy - ps[0].Y,
+	}
+	others := []truetype.Point(nil)
+	if ps[0].Flags&0x01 != 0 {
+		others = ps[1:]
+	} else {
+		last := fixed.Point26_6{
+			X: dx + ps[len(ps)-1].X,
+			Y: dy - ps[len(ps)-1].Y,
+		}
+		if ps[len(ps)-1].Flags&0x01 != 0 {
+			start = last
+			others = ps[:len(ps)-1]
+		} else {
+			start = fixed.Point26_6{
+				X: (start.X + last.X) / 2,
+				Y: (start.Y + last.Y) / 2,
+			}
+			others = ps
+		}
+	}
+	c.r.Start(start)
+	q0, on0 := start, true
+	for _, p := range others {
+		q := fixed.Point26_6{
+			X: dx + p.X,
+			Y: dy - p.Y,
+		}
+		on := p.Flags&0x01 != 0
+		if on {
+			if on0 {
+				c.r.Add1(q)
+			} else {
+				c.r.Add2(q0, q)
+			}
+		} else {
+			if on0 {
+				// No-op.
+			} else {
+				mid := fixed.Point26_6{
+					X: (q0.X + q.X) / 2,
+					Y: (q0.Y + q.Y) / 2,
+				}
+				c.r.Add2(q0, mid)
+			}
+		}
+		q0, on0 = q, on
+	}
+	// Close the curve.
+	if on0 {
+		c.r.Add1(start)
+	} else {
+		c.r.Add2(q0, start)
+	}
+}
+
+// rasterize returns the advance width, glyph mask and integer-pixel offset
+// to render the given glyph at the given sub-pixel offsets.
+// The 26.6 fixed point arguments fx and fy must be in the range [0, 1).
+func (c *frContext) rasterize(glyph truetype.Index, fx, fy fixed.Int26_6) (
+	fixed.Int26_6, *image.Alpha, image.Point, error) {
+
+	if err := c.glyphBuf.Load(c.f, c.scale, glyph, c.hinting); err != nil {
+		return 0, nil, image.Point{}, err
+	}
+	// Calculate the integer-pixel bounds for the glyph.
+	xmin := int(fx+c.glyphBuf.Bounds.Min.X) >> 6
+	ymin := int(fy-c.glyphBuf.Bounds.Max.Y) >> 6
+	xmax := int(fx+c.glyphBuf.Bounds.Max.X+0x3f) >> 6
+	ymax := int(fy-c.glyphBuf.Bounds.Min.Y+0x3f) >> 6
+	if xmin > xmax || ymin > ymax {
+		return 0, nil, image.Point{}, errors.New("freetype: negative sized glyph")
+	}
+	// A TrueType's glyph's nodes can have negative co-ordinates, but the
+	// rasterizer clips anything left of x=0 or above y=0. xmin and ymin are
+	// the pixel offsets, based on the font's FUnit metrics, that let a
+	// negative co-ordinate in TrueType space be non-negative in rasterizer
+	// space. xmin and ymin are typically <= 0.
+	fx -= fixed.Int26_6(xmin << 6)
+	fy -= fixed.Int26_6(ymin << 6)
+	// Rasterize the glyph's vectors.
+	c.r.Clear()
+	e0 := 0
+	for _, e1 := range c.glyphBuf.Ends {
+		c.drawContour(c.glyphBuf.Points[e0:e1], fx, fy)
+		e0 = e1
+	}
+	a := image.NewAlpha(image.Rect(0, 0, xmax-xmin, ymax-ymin))
+	c.r.Rasterize(raster.NewAlphaSrcPainter(a))
+	return c.glyphBuf.AdvanceWidth, a, image.Point{xmin, ymin}, nil
+}
+
+// glyph returns the advance width, glyph mask and integer-pixel offset to
+// render the given glyph at the given sub-pixel point. It is a cache for the
+// rasterize method. Unlike rasterize, p's co-ordinates do not have to be in
+// the range [0, 1).
+func (c *frContext) glyph(glyph truetype.Index, p fixed.Point26_6) (
+	fixed.Int26_6, *image.Alpha, image.Point, error) {
+
+	// Split p.X and p.Y into their integer and fractional parts.
+	ix, fx := int(p.X>>6), p.X&0x3f
+	iy, fy := int(p.Y>>6), p.Y&0x3f
+	// Calculate the index t into the cache array.
+	tg := int(glyph) % nGlyphs
+	tx := int(fx) / (64 / nXFractions)
+	ty := int(fy) / (64 / nYFractions)
+	t := ((tg*nXFractions)+tx)*nYFractions + ty
+	// Check for a cache hit.
+	if e := c.cache[t]; e.valid && e.glyph == glyph {
+		return e.advanceWidth, e.mask, e.offset.Add(image.Point{ix, iy}), nil
+	}
+	// Rasterize the glyph and put the result into the cache.
+	advanceWidth, mask, offset, err := c.rasterize(glyph, fx, fy)
+	if err != nil {
+		return 0, nil, image.Point{}, err
+	}
+	c.cache[t] = cacheEntry{true, glyph, advanceWidth, mask, offset}
+	return advanceWidth, mask, offset.Add(image.Point{ix, iy}), nil
+}
+
+const maxInt = int(^uint(0) >> 1)
+
+// DrawString draws s at p and returns p advanced by the text extent. The text
+// is placed so that the left edge of the em square of the first character of s
+// and the baseline intersect at p. The majority of the affected pixels will be
+// above and to the right of the point, but some may be below or to the left.
+// For example, drawing a string that starts with a 'J' in an italic font may
+// affect pixels below and left of the point.
+//
+// p is a fixed.Point26_6 and can therefore represent sub-pixel positions.
+func (c *frContext) drawString(s string, p fixed.Point26_6) (fixed.Point26_6, image.Rectangle, error) {
+	if c.f == nil {
+		return fixed.Point26_6{}, image.Rectangle{}, errors.New("freetype: DrawText called with a nil font")
+	}
+	bounds := image.Rectangle{Min: image.Point{X: maxInt, Y: maxInt}}
+	prev, hasPrev := truetype.Index(0), false
+	for _, rune := range s {
+		index := c.f.Index(rune)
+		if hasPrev {
+			kern := c.f.Kern(c.scale, prev, index)
+			if c.hinting != font.HintingNone {
+				kern = (kern + 32) &^ 63
+			}
+			p.X += kern
+		}
+		advanceWidth, mask, offset, err := c.glyph(index, p)
+		if err != nil {
+			return fixed.Point26_6{}, image.Rectangle{}, err
+		}
+		p.X += advanceWidth
+		glyphRect := mask.Bounds().Add(offset)
+		if glyphRect.Min.X < bounds.Min.X {
+			bounds.Min.X = glyphRect.Min.X
+		}
+		if glyphRect.Min.Y < bounds.Min.Y {
+			bounds.Min.Y = glyphRect.Min.Y
+		}
+		if glyphRect.Max.X > bounds.Max.X {
+			bounds.Max.X = glyphRect.Max.X
+		}
+		if glyphRect.Max.Y > bounds.Max.Y {
+			bounds.Max.Y = glyphRect.Max.Y
+		}
+		dr := c.clip.Intersect(glyphRect)
+		if !dr.Empty() {
+			mp := image.Point{0, dr.Min.Y - glyphRect.Min.Y}
+			draw.DrawMask(c.dst, dr, c.src, image.ZP, mask, mp, draw.Src)
+		}
+		prev, hasPrev = index, true
+	}
+	bounds = c.clip.Intersect(bounds)
+	return p, bounds, nil
+}
+
+// recalc recalculates scale and bounds values from the font size, screen
+// resolution and font metrics, and invalidates the glyph cache.
+func (c *frContext) recalc() {
+	c.scale = fixed.Int26_6(c.fontSize * c.dpi * (64.0 / 72.0))
+	if c.f == nil {
+		c.r.SetBounds(0, 0)
+	} else {
+		// Set the rasterizer's bounds to be big enough to handle the largest glyph.
+		b := c.f.Bounds(c.scale)
+		xmin := +int(b.Min.X) >> 6
+		ymin := -int(b.Max.Y) >> 6
+		xmax := +int(b.Max.X+63) >> 6
+		ymax := -int(b.Min.Y-63) >> 6
+		c.r.SetBounds(xmax-xmin, ymax-ymin)
+	}
+	for i := range c.cache {
+		c.cache[i] = cacheEntry{}
+	}
+}
+
+// SetDPI sets the screen resolution in dots per inch.
+func (c *frContext) setDPI(dpi float64) {
+	if c.dpi == dpi {
+		return
+	}
+	c.dpi = dpi
+	c.recalc()
+}
+
+// SetFont sets the font used to draw text.
+func (c *frContext) setFont(f *truetype.Font) {
+	if c.f == f {
+		return
+	}
+	c.f = f
+	c.recalc()
+}
+
+// SetFontSize sets the font size in points (as in "a 12 point font").
+func (c *frContext) setFontSize(fontSize float64) {
+	if c.fontSize == fontSize {
+		return
+	}
+	c.fontSize = fontSize
+	c.recalc()
+}
+
+// SetHinting sets the hinting policy.
+func (c *frContext) setHinting(hinting font.Hinting) {
+	c.hinting = hinting
+	for i := range c.cache {
+		c.cache[i] = cacheEntry{}
+	}
+}
+
+// SetDst sets the destination image for draw operations.
+func (c *frContext) setDst(dst draw.Image) {
+	c.dst = dst
+}
+
+// SetSrc sets the source image for draw operations. This is typically an
+// image.Uniform.
+func (c *frContext) setSrc(src image.Image) {
+	c.src = src
+}
+
+// SetClip sets the clip rectangle for drawing.
+func (c *frContext) setClip(clip image.Rectangle) {
+	c.clip = clip
+}
+
+// TODO(nigeltao): implement Context.SetGamma.
+
+// NewContext creates a new Context.
+func newFRContext() *frContext {
+	return &frContext{
+		r:        raster.NewRasterizer(0, 0),
+		fontSize: 12,
+		dpi:      72,
+		scale:    12 << 6,
+	}
+}

text.go

@@ -11,7 +11,7 @@ import (
 	"golang.org/x/image/math/fixed"
 )
 
-var fontRenderingContext = freetype.NewContext()
+var fontRenderingContext = newFRContext()
 
 type Font struct {
 	font *truetype.Font
@@ -56,30 +56,42 @@ func (cv *Canvas) FillText(str string, x, y float32) {
 		gli.TexParameteri(gl_TEXTURE_2D, gl_TEXTURE_MAG_FILTER, gl_NEAREST)
 		gli.TexParameteri(gl_TEXTURE_2D, gl_TEXTURE_WRAP_S, gl_CLAMP_TO_EDGE)
 		gli.TexParameteri(gl_TEXTURE_2D, gl_TEXTURE_WRAP_T, gl_CLAMP_TO_EDGE)
+		gli.TexImage2D(gl_TEXTURE_2D, 0, gl_RGBA, int32(cv.w), int32(cv.h), 0, gl_RGBA, gl_UNSIGNED_BYTE, nil)
 	}
 
-	for i := range cv.text.target.Pix {
-		cv.text.target.Pix[i] = 0
-	}
-
-	fontRenderingContext.SetFont(cv.text.font.font)
-	fontRenderingContext.SetFontSize(float64(cv.text.size))
-	fontRenderingContext.SetSrc(image.NewUniform(colorGLToGo(cv.fill.r, cv.fill.g, cv.fill.b, cv.fill.a)))
-	fontRenderingContext.SetDst(cv.text.target)
-	fontRenderingContext.SetClip(cv.text.target.Bounds())
-	fontRenderingContext.DrawString(str, fixed.Point26_6{X: fixed.Int26_6(x*64 + 0.5), Y: fixed.Int26_6(y*64 + 0.5)})
+	fontRenderingContext.setFont(cv.text.font.font)
+	fontRenderingContext.setFontSize(float64(cv.text.size))
+	fontRenderingContext.setSrc(image.NewUniform(colorGLToGo(cv.fill.r, cv.fill.g, cv.fill.b, cv.fill.a)))
+	fontRenderingContext.setDst(cv.text.target)
+	fontRenderingContext.setClip(cv.text.target.Bounds())
+	_, bounds, _ := fontRenderingContext.drawString(str, fixed.Point26_6{X: fixed.Int26_6(x*64 + 0.5), Y: fixed.Int26_6(y*64 + 0.5)})
+	subImg := cv.text.target.SubImage(bounds).(*image.RGBA)
 
 	gli.BlendFunc(gl_ONE, gl_ONE_MINUS_SRC_ALPHA)
 
 	gli.ActiveTexture(gl_TEXTURE0)
 	gli.BindTexture(gl_TEXTURE_2D, cv.text.tex)
-	gli.TexImage2D(gl_TEXTURE_2D, 0, gl_RGBA, int32(cv.w), int32(cv.h), 0, gl_RGBA, gl_UNSIGNED_BYTE, gli.Ptr(&cv.text.target.Pix[0]))
+
+	for y, w, h := 0, bounds.Dx(), bounds.Dy(); y < h; y++ {
+		off := y * subImg.Stride
+		pix := subImg.Pix
+		gli.TexSubImage2D(gl_TEXTURE_2D, 0, 0, int32(cv.h-1-y), int32(w), 1, gl_RGBA, gl_UNSIGNED_BYTE, gli.Ptr(&pix[off]))
+		for b := w * 4; b > 0; b-- {
+			pix[off] = 0
+			off++
+		}
+	}
 
 	gli.UseProgram(tr.id)
 	gli.Uniform1i(tr.image, 0)
 
 	gli.BindBuffer(gl_ARRAY_BUFFER, buf)
-	data := [16]float32{-1, -1, -1, 1, 1, 1, 1, -1, 0, 1, 0, 0, 1, 0, 1, 1}
+	x0 := float32(bounds.Min.X) / cv.fw
+	y0 := float32(bounds.Min.Y) / cv.fh
+	x1 := float32(bounds.Max.X) / cv.fw
+	y1 := float32(bounds.Max.Y) / cv.fh
+	data := [16]float32{x0*2 - 1, -y0*2 + 1, x0*2 - 1, -y1*2 + 1, x1*2 - 1, -y1*2 + 1, x1*2 - 1, -y0*2 + 1,
+		0, 1, 0, 1 - (y1 - y0), x1 - x0, 1 - (y1 - y0), x1 - x0, 1}
 	gli.BufferData(gl_ARRAY_BUFFER, len(data)*4, unsafe.Pointer(&data[0]), gl_STREAM_DRAW)
 
 	gli.VertexAttribPointer(tr.vertex, 2, gl_FLOAT, false, 0, nil)