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freetype/truetype: normalize and set dual vector for SPVFS and SFVFS

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opcodes. Calculate dot product with 32-bit math to match C Freetype's
rounding.

R=bsiegert
CC=golang-dev, remyoudompheng
https://codereview.appspot.com/32740043
This commit is contained in:
Nigel Tao 2013-11-27 17:48:57 +11:00
parent cce54f9bf8
commit 5a5d117404
2 changed files with 40 additions and 14 deletions
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52
freetype/truetype/hint.go
View file

@ -250,16 +250,12 @@ func (h *Hinter) run(program []byte, pCurrent, pUnhinted, pInFontUnits []Point,
case opSPVFS:
top -= 2
h.gs.pv[0] = f2dot14(h.stack[top+0])
h.gs.pv[1] = f2dot14(h.stack[top+1])
// TODO: normalize h.gs.pv ??
// TODO: h.gs.dv = h.gs.pv ??
h.gs.pv = normalize(f2dot14(h.stack[top]), f2dot14(h.stack[top+1]))
h.gs.dv = h.gs.pv
case opSFVFS:
top -= 2
h.gs.fv[0] = f2dot14(h.stack[top+0])
h.gs.fv[1] = f2dot14(h.stack[top+1])
// TODO: normalize h.gs.fv ??
h.gs.fv = normalize(f2dot14(h.stack[top]), f2dot14(h.stack[top+1]))
case opGPV:
if top+1 >= len(h.stack) {
@ -1624,13 +1620,43 @@ func (x f26dot6) mul(y f26dot6) f26dot6 {
return f26dot6(int64(x) * int64(y) >> 6)
}
// dotProduct returns the dot product of [x, y] and q.
// dotProduct returns the dot product of [x, y] and q. It is almost the same as
// px := int64(x)
// py := int64(y)
// qx := int64(q[0])
// qy := int64(q[1])
// return f26dot6((px*qx + py*qy + 1<<13) >> 14)
// except that the computation is done with 32-bit integers to produce exactly
// the same rounding behavior as C Freetype.
func dotProduct(x, y f26dot6, q [2]f2dot14) f26dot6 {
px := int64(x)
py := int64(y)
qx := int64(q[0])
qy := int64(q[1])
return f26dot6((px*qx + py*qy + 1<<13) >> 14)
// Compute x*q[0] as 64-bit value.
l := uint32((int32(x) & 0xFFFF) * int32(q[0]))
m := (int32(x) >> 16) * int32(q[0])
lo1 := l + (uint32(m) << 16)
hi1 := (m >> 16) + (int32(l) >> 31) + bool2int32(lo1 < l)
// Compute y*q[1] as 64-bit value.
l = uint32((int32(y) & 0xFFFF) * int32(q[1]))
m = (int32(y) >> 16) * int32(q[1])
lo2 := l + (uint32(m) << 16)
hi2 := (m >> 16) + (int32(l) >> 31) + bool2int32(lo2 < l)
// Add them.
lo := lo1 + lo2
hi := hi1 + hi2 + bool2int32(lo < lo1)
// Divide the result by 2^14 with rounding.
s := hi >> 31
l = lo + uint32(s)
hi += s + bool2int32(l < lo)
lo = l
l = lo + 0x2000
hi += bool2int32(l < lo)
return f26dot6((uint32(hi) << 18) | (l >> 14))
}
// mulDiv returns x*y/z, rounded to the nearest integer.

2
freetype/truetype/truetype_test.go
View file

@ -255,7 +255,7 @@ var scalingTestCases = []struct {
hintingBrokenAt int
}{
{"luxisr", 12, -1},
{"x-arial-bold", 11, 17},
{"x-arial-bold", 11, 94},
{"x-deja-vu-sans-oblique", 17, -1},
{"x-droid-sans-japanese", 9, 0},
{"x-times-new-roman", 13, 0},