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Fix crash when requesting A32 glyph on Wayland

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On Wayland we aren't getting any information about the subpixel
layout of the screen. On Freetype, this triggers an
assert / memory corruption when explicitly requesting a subpixel
antialiased glyph (via QRawFont) because it needs to know the
layout to render the glyphs.

It might be possible to get this information in the Wayland plugin,
but at least we should have a failsafe which doesn't crash when
the problem occurs. This simply falls back to using A8 antialiasing
when it doesn't know the subpixel layout.

[ChangeLog][Freetype] Fixed crash when calling
QRawFont::alphaMapForGlyph() with subpixel antialiasing on Wayland.

Fixes: QTBUG-90236
Change-Id: Iddee2e171a81664ae9e3989115881f23262b2182
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>
(cherry picked from commit ef763e195892a6d8ce207f5d947fe508f645cb6d)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
This commit is contained in:
Eskil Abrahamsen Blomfeldt 2021-02-05 12:36:37 +01:00 committed by Qt Cherry-pick Bot
parent fd15b28cf8
commit 9807573764
1 changed files with 5 additions and 1 deletions
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6
src/gui/text/freetype/qfontengine_ft.cpp
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@ -1078,7 +1078,11 @@ QFontEngineFT::Glyph *QFontEngineFT::loadGlyph(QGlyphSet *set, uint glyph,
renderMode = FT_RENDER_MODE_MONO;
break;
case Format_A32:
Q_ASSERT(hsubpixel || vfactor != 1);
if (!hsubpixel && vfactor == 1) {
qWarning("Format_A32 requested, but subpixel layout is unknown.");
return nullptr;
}
renderMode = hsubpixel ? FT_RENDER_MODE_LCD : FT_RENDER_MODE_LCD_V;
break;
case Format_A8: