Draw the `building` layer at the top two zooms, stippled to every other dot.
On a braille canvas a dot is one bit, so a solid fill does not shade a region
— it lights every dot in every cell it covers and takes the street grid down
with it. Downtown becomes a wall of ⣿ with the roads gone. The stipple reads
as tone instead, and leaves room in every cell for a road to stay a legible
line through it. Outlines fail differently: at one bit a building's edge and a
road are the same mark.
The lattice is aligned to the canvas rather than to each polygon, so
neighbouring footprints share it and the texture doesn't shimmer at their
seams.
Below the gate a typical footprint is about two dots across — under half a
cell — and the layer collapses into a haze, so it stays off.
Each footprint is rejected on its own tile-local bounds before a single point
of it is projected. Without that, a downtown tile's 2,704 footprints cost the
frame 2-4x (87 -> 258 ms at z15, 82 -> 294 ms at z16, measured on the fixture);
with it, +7% at z15 and +14% at z16, and flat in zoom. Widening DRAWN_LAYERS
re-stamps the decoded sidecar, so this costs one re-decode per tile and no
re-download.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Jean-Pierre MartineauandClaude Opus 5
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