Stage 1 (render-on-demand) removed the idle / whole-system freeze, but
panning a loaded map with "visible hyperspace" on stayed heavy in Safari:
the fog still cut its visibility holes by opaque overpaint — on KNNTS041
that is ~260 near-world-sized opaque circles blended over the fog every
rendered frame, a fill-rate cliff for Safari's WebGPU / Apple's tile-based
GPU.
Replace the overpaint with an INVERSE stencil mask: setVisibilityFog now
draws the FOG_COLOR rectangle(s) into fogLayer and collects the visibility
circles into one Graphics set as fogLayer.setMask({ mask, inverse: true }),
so the fog shows everywhere except the union of the circles. Per-frame cost
drops from dozens of blended opaque circle fills to one rect fill + a
stencil pass (no colour writes), which Apple's TBDR GPU handles cheaply,
and the fog stays fully vector — crisp at any zoom.
fogPaintOps and its unit tests are unchanged (the circle ops now feed the
mask instead of an overpaint). Verified with a high-contrast screenshot
during development (fog field with a correct circle-union hole) plus the
existing fog / render-on-demand e2e green on chromium + webkit.
Docs: renderer.md fog section + PLAN.md Phase 29 decision 9.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Ilia Denisov
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