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v31: long worksheets no longer crawl on Mac (Retina) screens - #32
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The overlay drew ink on one canvas as tall as the whole worksheet. On a 2x screen a 20-page worksheet made that canvas about 22,000 pixels tall. Chrome can only hand a canvas up to 16,384 pixels to the graphics chip; past that it draws with the main processor, and each pen move took about a tenth of a second. The lab's 1x screens stayed under the limit, which is why the same file was fine there. Now the canvas is a band about three screens tall that follows the scrolling and redraws when it moves. Ink is saved in the same place as before, so existing ink lines up. Measured on the reported worksheet: drawing went from about 9 to 60 frames a second on a 2x screen. Co-Authored-By: Claude Opus 5.5 <[email protected]>
Co-Authored-By: Claude Opus 5.5 <[email protected]>
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Fixes #31
What was wrong: the overlay drew ink on one canvas as tall as the whole worksheet. On the MacBook's 2× (Retina) screen, the Resume Day 2 packet made that canvas 2940 × 21,888 pixels. Chrome can only give a canvas up to 16,384 pixels tall to the graphics chip; past that it falls back to the main processor, and every pen move took ~110 ms (about 9 frames a second). The lab HPs have 1× screens, so the same canvas was 10,944 px tall — under the limit, and smooth.
Measured in Chrome at 2×: a canvas exactly 16,384 px tall drew at 60 fps; 16,385 px dropped right away. The highlighter's blend mode made no difference.
The fix: the canvas is now a band about three screens tall that follows the scrolling, and redraws when you scroll near its edge (or before a stroke starts, after a big jump). It's capped under the graphics-chip limit, so ink stays full sharpness.
Checked on the reported worksheet (headless Chrome):
To get it into a worksheet: open the
_board.htmlfile in OverBoard again — it upgrades the overlay to v31 and keeps the ink saved inside it.Only the HTML overlay changed; the PDF app already uses one canvas per page, so it never hit this.
🤖 Generated with Claude Code