A coarse pan step is 30% of the view, so four keypresses leave nothing of
the last frame under the screen — there is no ground to reproject, and the
map went black. It then stayed black for a whole raster, which is most of
a second on the PicoCalc, and often for two: the raster in flight was
being drawn for a view the user had already left, and the one they were
actually looking at could not start until it finished.
So the raster is two passes now. The first draws the ground fills, the
watercourses and the through-roads (tertiary and up, derived from the road
styles so the two sets cannot drift) — no buildings, no back streets, no
text at all. It is a quarter of the work: 249 ms against 962 at zoom 13 on
the device, 120 against 529 at zoom 16. The second draws the finished
frame over it.
The gap between them is where a moving view gets off. Checking _wanted
there cuts the abandonable unit of work from a whole raster to the rough
one, so a pan being held is answered with real ground about four times as
often and the finished frame is drawn for where the user actually stopped.
Measured on the device, four quick pan steps from a settled map to the
first ground back on screen:
zoom 13: 1984 ms -> 617 ms
zoom 15: 970 ms -> 348 ms
The rough pass is skipped where a frame for this view is already on screen
and merely waiting on a tile: there a coarser picture would take away
detail the reader can already see.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Jean-Pierre MartineauandClaude Opus 5
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