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Bug 380484. Don't divide by zero if a font has a really small maxAdvance. r=vlad

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roc+@cs.cmu.edu 2007-05-20 18:56:10 -07:00
parent d6f07e5be0
commit 28dcf3f8e0
1 changed files with 11 additions and 3 deletions
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14
gfx/thebes/src/gfxAtsuiFonts.cpp
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@ -476,9 +476,17 @@ FindTextRunSegmentLength(gfxTextRun *aTextRun, PRUint32 aOffset, PRUint32 aMaxLe
PRUint32
gfxAtsuiFontGroup::GuessMaximumStringLength()
{
gfxFloat maxAdvance = GetFontAt(0)->GetMetrics().maxAdvance;
// ATSUI can't handle offsets of more than 32K pixels
PRUint32 chars = 0x7FFF/PRUint32(maxAdvance);
// ATSUI can't handle offsets of more than 32K pixels. This function
// guesses a string length that ATSUI will be able to handle. We want to
// get the right answer most of the time, but if we're wrong in either
// direction, we won't break things: if we guess too large, our glyph
// processing will detect ATSUI's failure and retry with a smaller limit.
// If we guess too small, we'll just break the string into more pieces
// than we strictly needed to.
// The basic calculation is just 32k pixels divided by the font max-advance,
// but we need to be a bit careful to avoid math errors.
PRUint32 maxAdvance = PRUint32(GetFontAt(0)->GetMetrics().maxAdvance);
PRUint32 chars = 0x7FFF/PR_MAX(1, maxAdvance);
return PR_MAX(1, chars);
}