As opposed to the raster engine, in Qt Quick we are using
unscaled positions for the glyphs and using the vertex shader
to scale these after the fact. However, when picking the
correct subpixel rendering for each glyph, we would use the
unscaled position's fractional part, meaning that we
essentially rendered the glyphs at the wrong subpixel position.
This was especially visible when doing fractional scaling, e.g.
125%.
Thus we need to get the fraction of the actual on-screen position
instead. This has to be done both when populating the cache for
the Qt Quick case (this enabler adds it as opt-in) and also when
actually selecting the correct rendering of the glyph (change in
Qt Declarative).
Pick-to: 5.15 6.2 6.3 6.4
Task-number: QTBUG-101008
Change-Id: Ie67948b138f578b5f40d6a950c4aa92394a8f09a
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
20ae170b35