// rasterize returns the advance width, glyph mask and integer-pixel offset
// to render the given glyph at the given sub-pixel offsets.
// The 24.8 fixed point arguments fx and fy must be in the range [0, 1).
func (c *Context) rasterize(glyph truetype.Index, fx, fy raster.Fix32) (
raster.Fix32, *image.Alpha, image.Point, error) {
if err := c.glyphBuf.Load(c.font, c.scale, glyph, truetype.Hinting(c.hinting)); err != nil {
return 0, nil, image.Point{}, err
}
// Calculate the integer-pixel bounds for the glyph.
xmin := int(fx+raster.Fix32(c.glyphBuf.B.XMin<<2)) >> 8
ymin := int(fy-raster.Fix32(c.glyphBuf.B.YMax<<2)) >> 8
xmax := int(fx+raster.Fix32(c.glyphBuf.B.XMax<<2)+0xff) >> 8
ymax := int(fy-raster.Fix32(c.glyphBuf.B.YMin<<2)+0xff) >> 8
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 += raster.Fix32(-xmin << 8)
fy += raster.Fix32(-ymin << 8)
// Rasterize the glyph's vectors.
c.r.Clear()
e0 := 0
for _, e1 := range c.glyphBuf.End {
c.drawContour(c.glyphBuf.Point[e0:e1], fx, fy)
e0 = e1
}
a := image.NewAlpha(image.Rect(0, 0, xmax-xmin, ymax-ymin))
c.r.Rasterize(raster.NewAlphaSrcPainter(a))
return raster.Fix32(c.glyphBuf.AdvanceWidth << 2), a, image.Point{xmin, ymin}, nil
}
func (f *font) glyph(r rune) *glyph {
if g, found := f.glyphs[r]; found {
return g
}
idx := f.ttf.Index(r)
gb := truetype.NewGlyphBuf()
err := gb.Load(f.ttf, f.scale, idx, truetype.Hinting(truetype.FullHinting))
if err != nil {
panic(err)
}
g := glyph(*gb)
f.glyphs[r] = &g
return &g
}