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Loosen the SLOOP (Set LOOP) opcode precondition.

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This goes against spec, but matches the C Freetype implementation and
works around a bug in DejaVuSansMono.ttf's hinted '2' glyph.
This commit is contained in:
Nigel Tao 2016-05-19 16:14:08 +10:00
parent c67e4d98d2
commit a31d0146da
1 changed files with 8 additions and 1 deletions
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9
truetype/hint.go
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@ -341,7 +341,14 @@ func (h *hinter) run(program []byte, pCurrent, pUnhinted, pInFontUnits []Point,
case opSLOOP:
top--
if h.stack[top] <= 0 {
// https://developer.apple.com/fonts/TrueType-Reference-Manual/RM05/Chap5.html#SLOOP
// says that "Setting the loop variable to zero is an error". In
// theory, the inequality on the next line should be "<=" instead
// of "<". In practice, some font files' bytecode, such as the '2'
// glyph in the DejaVuSansMono.ttf that comes with Ubuntu 14.04,
// issue SLOOP with a zero on top of the stack. Just like the C
// Freetype code, we allow the zero.
if h.stack[top] < 0 {
return errors.New("truetype: hinting: invalid data")
}
h.gs.loop = h.stack[top]