Zbigniew Jędrzejewski-Szmek wrote: > With python3-pyqt6-6.8.0-0.1.fc42.x86_64, we get a difference in how the > icons are rendered: > > calibre-7.20.0-1.fc42.x86_64 > modified-S.5........ > /usr/share/icons/hicolor/16x16/apps/calibre-gui.png > modified-S.5........ > /usr/share/icons/hicolor/32x32/apps/calibre-ebook-edit.png > modified-S.5........ > /usr/share/icons/hicolor/32x32/apps/calibre-gui.png > modified-S.5........ > /usr/share/icons/hicolor/32x32/apps/calibre-viewer.png ... > > There are some tiny differences in shading of some pixels. The difference > is not discernible visually for me. [1] has example icons attached. > > Is this a bug in Qt and implementation of QImage.scaled [3] ?
As I understand the Qt source code, QImage.scaled with the Qt.TransformationMode.SmoothTransformation flag ends up calling QImage.smoothScaled (QImage.scaled calls the general QImage.transformed, which then detects the special case and calls QImage.smoothScaled), which in turn calls the private qSmoothScaleImage. And that one uses a different algorithm based on whether the CPU is runtime-detected to support SSE 4.1 or not. (For non-x86, there are also optimized implementations for ARM NEON and Longsoon LSX, also with runtime detection, otherwise the generic C implementation is used, as on pre-SSE-4.1 x86.) See https://code.qt.io/cgit/qt/qtbase.git/tree/src/gui/painting/qimagescale.cpp and https://code.qt.io/cgit/qt/qtbase.git/tree/src/gui/painting/qimagescale_sse4.cpp . It is likely that the vectorized implementation rounds slightly differently. So you then end up with different results when building on non- identical builder hardware. Kevin Kofler -- _______________________________________________ devel mailing list -- devel@lists.fedoraproject.org To unsubscribe send an email to devel-le...@lists.fedoraproject.org Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org Do not reply to spam, report it: https://pagure.io/fedora-infrastructure/new_issue
