https://bugs.kde.org/show_bug.cgi?id=526691
Bug ID: 526691
Summary: SVG cursor themes are blurry on scaled outputs when
shapes use SVG filters (QtSvg ignores
devicePixelRatio)
Classification: Plasma
Product: kwin
Version First 6.7.5
Reported In:
Platform: Fedora RPMs
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: wayland-generic
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
Created attachment 196853
--> https://bugs.kde.org/attachment.cgi?id=196853&action=edit
Screenshot showing the bug (left-most) and the cursors with fix applied
DESCRIPTION
SvgCursorReader::load() renders each SVG with QSvgRenderer into a QImage that
has setDevicePixelRatio(devicePixelRatio). QtSvg rasterises everything under an
SVG filter at logical resolution in that case
(https://qt-project.atlassian.net/browse/QTBUG-151165), so cursor themes whose
shapes sit inside a drop-shadow group are upscaled 2x on a 200 % output. Breeze
is unaffected only because its filter is on the separate shadow path.
Observed with a macOS-style cursor theme (Figma drop shadows around the whole
shape): blurry over Plasma surfaces (Qt clients use cursor-shape-v1, so KWin
renders the cursor) and sharp over Chromium windows (which use the XCursor
images).
SUGGESTED WORKAROUND
Render at DPR 1 with the device pixel size and set the ratio afterwards:
```
QImage image(bounds.size() * devicePixelRatio,
QImage::Format_ARGB32_Premultiplied);
image.fill(Qt::transparent);
QPainter painter(&image);
renderer.render(&painter, QRectF(QPointF(0, 0), QSizeF(bounds.size()) *
devicePixelRatio));
painter.end();
image.setDevicePixelRatio(devicePixelRatio);
```
Measured with QtSvg 6.11.2 on the affected theme's arrow at size 30, DPR 2:
mean alpha difference to a librsvg reference drops from 8.4/255 to 0.7/255. Not
built or tested inside KWin itself.
SOFTWARE/OS VERSIONS
Operating System: Fedora Linux 44
KDE Plasma Version: 6.7.5
KDE Frameworks Version: 6.30.0
Qt Version: 6.11.2
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