// rasterize returns the 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) (*image.Alpha, image.Point, error) {
if err := c.glyphBuf.Load(c.font, glyph); err != nil {
return nil, image.ZP, err
}
// Calculate the integer-pixel bounds for the glyph.
xmin := int(fx+c.FUnitToFix32(+int(c.glyphBuf.B.XMin))) >> 8
ymin := int(fy+c.FUnitToFix32(-int(c.glyphBuf.B.YMax))) >> 8
xmax := int(fx+c.FUnitToFix32(+int(c.glyphBuf.B.XMax))+0xff) >> 8
ymax := int(fy+c.FUnitToFix32(-int(c.glyphBuf.B.YMin))+0xff) >> 8
if xmin > xmax || ymin > ymax {
return nil, image.ZP, 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 a, image.Point{xmin, ymin}, nil
}
func main() {
const (
n = 17
r = 256 * 80
)
s := raster.Fix32(r * math.Sqrt(2) / 2)
t := raster.Fix32(r * math.Tan(math.Pi/8))
m := image.NewRGBA(image.Rect(0, 0, 800, 600))
draw.Draw(m, m.Bounds(), &image.Uniform{color.RGBA{63, 63, 63, 255}}, image.ZP, draw.Src)
mp := raster.NewRGBAPainter(m)
mp.SetColor(image.Black)
z := raster.NewRasterizer(800, 600)
for i := 0; i < n; i++ {
cx := raster.Fix32(25600 + 51200*(i%4))
cy := raster.Fix32(2560 + 32000*(i/4))
c := raster.Point{cx, cy}
theta := math.Pi * (0.5 + 0.5*float64(i)/(n-1))
dx := raster.Fix32(r * math.Cos(theta))
dy := raster.Fix32(r * math.Sin(theta))
d := raster.Point{dx, dy}
// Draw a quarter-circle approximated by two quadratic segments,
// with each segment spanning 45 degrees.
z.Start(c)
z.Add1(c.Add(raster.Point{r, 0}))
z.Add2(c.Add(raster.Point{r, t}), c.Add(raster.Point{s, s}))
z.Add2(c.Add(raster.Point{t, r}), c.Add(raster.Point{0, r}))
// Add another quadratic segment whose angle ranges between 0 and 90 degrees.
// For an explanation of the magic constants 22, 150, 181 and 256, read the
// comments in the freetype/raster package.
dot := 256 * d.Dot(raster.Point{0, r}) / (r * r)
multiple := raster.Fix32(150 - 22*(dot-181)/(256-181))
z.Add2(c.Add(raster.Point{dx, r + dy}.Mul(multiple)), c.Add(d))
// Close the curve.
z.Add1(c)
}
z.Rasterize(mp)
for i := 0; i < n; i++ {
cx := raster.Fix32(25600 + 51200*(i%4))
cy := raster.Fix32(2560 + 32000*(i/4))
for j := 0; j < n; j++ {
theta := math.Pi * float64(j) / (n - 1)
dx := raster.Fix32(r * math.Cos(theta))
dy := raster.Fix32(r * math.Sin(theta))
m.Set(int((cx+dx)/256), int((cy+dy)/256), color.RGBA{255, 255, 0, 255})
}
}
// Save that RGBA image to disk.
f, err := os.Create("out.png")
if err != nil {
log.Println(err)
os.Exit(1)
}
defer f.Close()
b := bufio.NewWriter(f)
err = png.Encode(b, m)
if err != nil {
log.Println(err)
os.Exit(1)
}
err = b.Flush()
if err != nil {
log.Println(err)
os.Exit(1)
}
fmt.Println("Wrote out.png OK.")
}
func p(n node) raster.Point {
x, y := 20+n.x/4, 380-n.y/4
return raster.Point{raster.Fix32(x * 256), raster.Fix32(y * 256)}
}
// FUnitToFix32 converts the given number of FUnits into fixed point units,
// rounding to nearest.
func (c *Context) FUnitToFix32(x int) raster.Fix32 {
return raster.Fix32((x*c.scale + 128) >> 8)
}
// Pt converts from a co-ordinate pair measured in pixels to a raster.Point
// co-ordinate pair measured in raster.Fix32 units.
func Pt(x, y int) raster.Point {
return raster.Point{raster.Fix32(x << 8), raster.Fix32(y << 8)}
}
// PointToFix32 converts the given number of points (as in ``a 12 point font'')
// into fixed point units.
func (c *Context) PointToFix32(x float64) raster.Fix32 {
return raster.Fix32(x * float64(c.dpi) * (256.0 / 72.0))
}
func p(x, y int) raster.Point {
return raster.Point{raster.Fix32(x * 256), raster.Fix32(y * 256)}
}