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Bug 1823888 - Clamp scale factor used in computing synthetic-bold offsets, to avoid bad print/pdf output. r=dholbert

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Differential Revision: https://phabricator.services.mozilla.com/D174864
This commit is contained in:
Jonathan Kew 2023-05-04 11:10:01 +00:00
parent 60af7a6d26
commit 6a99f49fca
1 changed files with 18 additions and 1 deletions
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19
gfx/thebes/gfxFont.cpp
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@ -2445,7 +2445,21 @@ void gfxFont::Draw(const gfxTextRun* aTextRun, uint32_t aStart, uint32_t aEnd,
// need to handle it here.
bool doMultistrikeBold = ApplySyntheticBold() && !textDrawer;
if (doMultistrikeBold) {
gfx::Float xscale = CalcXScale(aRunParams.context->GetDrawTarget());
// For screen display, we want to try and repeat strikes with an offset of
// one device pixel, accounting for zoom or other transforms that may be
// in effect, so compute x-axis scale factor from the drawtarget.
// However, when generating PDF output the drawtarget's transform does not
// really bear any relation to "device pixels", and may result in an
// excessively large offset relative to the font size (bug 1823888), so
// we limit it based on the used font size to avoid this.
// The constant 48.0 reflects the threshold where the calculation in
// gfxFont::GetSyntheticBoldOffset() switches to a simple origin-based
// slope, though the exact value is somewhat arbitrary; it's selected to
// allow a visible amount of boldness while preventing the offset from
// becoming "large" in relation to the glyphs.
Float xscale =
std::min<Float>(GetAdjustedSize() / 48.0,
CalcXScale(aRunParams.context->GetDrawTarget()));
fontParams.synBoldOnePixelOffset = aRunParams.direction * xscale;
if (xscale != 0.0) {
static const int32_t kMaxExtraStrikes = 128;
@ -2461,6 +2475,9 @@ void gfxFont::Draw(const gfxTextRun* aTextRun, uint32_t aStart, uint32_t aEnd,
// use as many strikes as needed for the increased advance
fontParams.extraStrikes = NS_lroundf(std::max(1.0, extraStrikes));
}
} else {
// Degenerate transform?!
fontParams.extraStrikes = 0;
}
} else {
fontParams.synBoldOnePixelOffset = 0;