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Freetype: Fix transformed text when subpixel AA is on

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6ba003f73295b896aa6dc1fba099daadb4760209 fixed transforming
bitmap fonts for the case where 8 bit antialiasing is used.
This is the case when a transform is set on the painter by
the user, but for some reason it is not when high-dpi is
enabled, triggering QTBUG-111796.

An attempt was made at fixing this by drawing the
untransformed glyphs into the cache and then transforming
them as they were put on the screen. This worked with
Qt Quick, but the raster engine does not support this and
instead falls back to QPainterPath rendering in that case.
So b492582b9c4cf679109ed4875aff912e186263cb caused a
regression and was reverted.

A simpler fix which works for both Qt Quick and QPainter
is to draw the pre-transformed image of the glyph into
the cache for 24-bit AA, same as for 8-bit AA.

In addition, this changes the transformation to nearest
neighbor instead of interpolating, because bitmap fonts
are typically intended to look crisp and it also matches
how native rendered fonts are scaled in Qt Quick.

Fixes: QTBUG-111796
Change-Id: I2d9fd9d98d32820e677916c3d1c744331a72175b
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>
(cherry picked from commit b6247ced7e83af4d51ba20be8068f28cc8c006bc)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
This commit is contained in:
Eskil Abrahamsen Blomfeldt 2024-11-06 15:59:22 +01:00 committed by Qt Cherry-pick Bot
parent 60065cc08e
commit 3a0e4b6147
1 changed files with 9 additions and 2 deletions
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11
src/gui/text/freetype/qfontengine_ft.cpp
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@ -2095,7 +2095,7 @@ QImage QFontEngineFT::alphaMapForGlyph(glyph_t g,
QImage img = alphaMapFromGlyphData(glyph, neededFormat); QImage img = alphaMapFromGlyphData(glyph, neededFormat);
if (needsImageTransform) if (needsImageTransform)
img = img.transformed(t, Qt::SmoothTransformation); img = img.transformed(t, Qt::FastTransformation);
else else
img = img.copy(); img = img.copy();
@ -2112,12 +2112,19 @@ QImage QFontEngineFT::alphaRGBMapForGlyph(glyph_t g,
if (t.type() > QTransform::TxRotate) if (t.type() > QTransform::TxRotate)
return QFontEngine::alphaRGBMapForGlyph(g, subPixelPosition, t); return QFontEngine::alphaRGBMapForGlyph(g, subPixelPosition, t);
const bool needsImageTransform = !FT_IS_SCALABLE(freetype->face)
&& t.type() > QTransform::TxTranslate;
const GlyphFormat neededFormat = Format_A32; const GlyphFormat neededFormat = Format_A32;
Glyph *glyph = loadGlyphFor(g, subPixelPosition, neededFormat, t, false, true); Glyph *glyph = loadGlyphFor(g, subPixelPosition, neededFormat, t, false, true);
QImage img = alphaMapFromGlyphData(glyph, neededFormat); QImage img = alphaMapFromGlyphData(glyph, neededFormat);
img = img.copy(); if (needsImageTransform)
img = img.transformed(t, Qt::FastTransformation);
else
img = img.copy();
if (!cacheEnabled && glyph != &emptyGlyph) if (!cacheEnabled && glyph != &emptyGlyph)
delete glyph; delete glyph;