The dimming outside the crop box was four quads, each joining a side of the
photo to the matching side of the box. Aligned, that is the photo minus the
box; rotated, the quads cross themselves and each other, so wedges inside the
box were dimmed and wedges outside doubly dark, growing with the angle (the
reporter's -45° shows it best). The export was never affected: the overlay
alone was wrong.
The dimming is now `outside_crop_mesh`: the photo's rectangle minus the box,
as one mesh of four disjoint half-strips (outside edge i, inside edge i+1,
clipped to the photo). A flat or non-finite box dims nothing.
Tests: a coverage test over several box sizes and angles (every photo point
outside the box in exactly one triangle, none inside the box or outside the
photo), a degenerate-box test, and a headless pixel test at -45° (inside the
box the frame matches the 0° frame; the photo's corner is dimmed), which
failed on the old mesh.
Jason Baldwin
60844cf162