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Fix integer overflow for very large fonts

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This caused glitches up to unreadable text with i.e.
pixelSize 256 and stretch factor 4x /* ((256*4)<<16)<<6 */.

Change-Id: Ib6a038a043d820a94bd2019c50390a815a2a8277
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
This commit is contained in:
Konstantin Ritt 2013-04-12 21:01:36 +03:00 committed by The Qt Project
parent 4f400eeec1
commit d3938c1898
1 changed files with 7 additions and 3 deletions
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10
src/gui/text/qfontengine.cpp
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@ -263,11 +263,15 @@ void *QFontEngine::harfbuzzFont() const
{ {
HB_FontRec *hbFont = (HB_FontRec *)font_; HB_FontRec *hbFont = (HB_FontRec *)font_;
if (!hbFont->x_ppem) { if (!hbFont->x_ppem) {
QFixed emSquare = emSquareSize(); qint64 emSquare = emSquareSize().truncate();
Q_ASSERT(emSquare == emSquareSize().toInt()); // ensure no truncation
if (emSquare == 0)
emSquare = 1000; // a fallback value suitable for Type1 fonts
hbFont->y_ppem = fontDef.pixelSize; hbFont->y_ppem = fontDef.pixelSize;
hbFont->x_ppem = fontDef.pixelSize * fontDef.stretch / 100; hbFont->x_ppem = fontDef.pixelSize * fontDef.stretch / 100;
hbFont->x_scale = (QFixed(hbFont->x_ppem * (1 << 16)) / emSquare).value(); // same as QFixed(x)/QFixed(emSquare) but without int32 overflow for x
hbFont->y_scale = (QFixed(hbFont->y_ppem * (1 << 16)) / emSquare).value(); hbFont->x_scale = (((qint64)hbFont->x_ppem << 6) * 0x10000L + (emSquare >> 1)) / emSquare;
hbFont->y_scale = (((qint64)hbFont->y_ppem << 6) * 0x10000L + (emSquare >> 1)) / emSquare;
} }
return font_; return font_;
} }