Hi! The reason for rounding is that the subpixel position of the glyphs is baked into the cached rendering of the glyph itself (so horizontal position x.5 would be a different cached object than x.0, but they should both be rendered at pixel x). It's a bit complex because the projected positions of the glyphs are calculated later, in the vertex shader, so you need to do some precalculation to produce something which aligns with the pixel edge when the final scale is applied. I believe the reason retina is mentioned there specifically is just because it's the first place we supported DPI-scaling, but it's not exclusive to Apple anymore.
Which Qt version is in use here? I did fix some bugs related to this, e.g. https://codereview.qt-project.org/c/qt/qtdeclarative/+/417675 and https://codereview.qt-project.org/c/qt/qtdeclarative/+/376361 Most of my testing was on Windows, though, so it sounds like there could still be issues on Wayland. Eskil Abrahamsen Blomfeldt Senior Manager, Graphics The Qt Company Sandakerveien 116 0484 Oslo, Norway eskil.abrahamsen-blomfe...@qt.io http://qt.io ________________________________ From: Development <development-boun...@qt-project.org> on behalf of Kai Uwe Broulik <k...@privat.broulik.de> Sent: Monday, August 28, 2023 6:22 PM To: development@qt-project.org <development@qt-project.org> Subject: [Development] QSGText: Why round glyph position like this? Hi everyone, while investigating blurry font with native renderer in QML apps in Plasma 6 under Wayland with fractional scaling (devicePixelRatio 1.75 in my case), I stumbled upon QSGTextMaskMaterial::populate which rounds the glyph position [1] citing Mac OS behavior. When I remove the rounding, font appears rendered correctly on my system (sorry for attachment ;), but this code hasn’t changed since 2014 and I am not very knowledgeable in this part of Qt. It’s also flooring the X and rounding the Y coordinate. What’s the deal with that? Tor Arne, can you perhaps shed some light on this? Cheers Kai Uwe [1] https://code.qt.io/cgit/qt/qtdeclarative.git/tree/src/quick/scenegraph/qsgdefaultglyphnode_p.cpp#n455
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