The canvas handling code work in widget (scaled) logical pixel space, but the OpenGL shaders work in (unscaled) device pixel space, which is probably what causing issues.
I also suspect the wrong scaling algorithm is chosen since it doesn't take into account the devicePixelRatioF() scale, but that is another issue...
| Status | Assigned | Task | ||
|---|---|---|---|---|
| Open | dkazakov | T2299 Make the canvas behave in HiDPI mode | ||
| Open | None | T7063 Instant preview rendering not working in HiDPI mode |
So it turns out that the stutter also happens with HiDPI disabled, though only at a lower zoom level :/
Though, after D7982 is applied, on a 2x dpi scale and 50% zoom level it is rather obvious that the wrong LoD plane is being used, especially when using a pixel brush.