[DevomB]

This is the desktop audit's hidpi-scale-fractional-odd-geometry finding.

wlroots' scene places a surface at round(x × scale) and sizes it as round((x + w) × scale) − round(x × scale) (wlr_scene.c scale_box). When x × scale is not whole, the on-screen size of a buffer drawn at round(w × scale) differs from the buffer by one pixel. That happens for an odd x at 1.5, or an x that is not a multiple of 4 at 1.25. pixman then takes its transform path: soft, and repeated on every redraw, even for Firefox, which draws at the exact scale. dwl's tiles start wherever mfact and the 6 px border put them, so most windows were off the grid.

Stacked: based on #675 (lock-follows-scale). The read is this commit only, 3f849c8. It goes in a batch after #675.

• tools/desktop/dwl-zone-borders.py: two edits.
  • A snaptopixel(Client *c) placed before resize. At a scale that is a whole number of quarters but not whole, it moves the surface's origin (geom + bw, relative to the monitor) up to the next multiple of the step: 2 at 1.5, 4 at 1.25 and 1.75. Any other scale is left as it is.
  • Its call in resize, after applybounds.
  • A tiled window takes the step from its width and height, so it stays inside its tile. Tiles are recomputed by every arrange, so nothing builds up.
  • A floating window only moves, so dragging it doesn't shrink it. Fullscreen sits at 0 with no border, so it doesn't change.
  • The (int)c->bw keeps the arithmetic signed for a floating window left of its monitor.
• tools/tests/dwl-headless.sh:
  • At scale 1 the one window must be configured at 1280×720 minus the border. This is the control.
  • kryptik-display, built there against wlroots' output-management XML, then applies * 1.25. The window must now be configured smaller by the step from the border to the next multiple of 4: 1010×562 with borderpx 6, where unsnapped would be 1012×564.
• docs/design/laptop.md: the grid, and the check.

Evidence: the headless check runs in CI's Compositor build job, and it tests the snapping arithmetic through dwl itself. That the pixman scaling then goes away follows from scale_box. No screenshot checks it.