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freetype: fix drawContour when the first point is off the curve.

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Fixes issue 16.

LGTM=crawshaw
R=crawshaw
CC=golang-codereviews, philipz
https://codereview.appspot.com/209280043
This commit is contained in:
Nigel Tao 2015-03-09 11:32:30 +11:00
parent 78edcde0f3
commit 160e1d6137
1 changed files with 31 additions and 4 deletions
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35
freetype/freetype.go
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@ -94,16 +94,43 @@ func (c *Context) drawContour(ps []truetype.Point, dx, dy raster.Fix32) {
if len(ps) == 0 {
return
}
// 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)
// 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 := raster.Point{
X: dx + raster.Fix32(ps[0].X<<2),
Y: dy - raster.Fix32(ps[0].Y<<2),
}
others := []truetype.Point(nil)
if ps[0].Flags&0x01 != 0 {
others = ps[1:]
} else {
last := raster.Point{
X: dx + raster.Fix32(ps[len(ps)-1].X<<2),
Y: dy - raster.Fix32(ps[len(ps)-1].Y<<2),
}
if ps[len(ps)-1].Flags&0x01 != 0 {
start = last
others = ps[:len(ps)-1]
} else {
start = raster.Point{
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 ps[1:] {
for _, p := range others {
q := raster.Point{
X: dx + raster.Fix32(p.X<<2),
Y: dy - raster.Fix32(p.Y<<2),