Optimize display list walk to one pass - #21
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To find how far an item may draw from a pixel, every renderer called *_find_max_line_len(), which scanned all the items above the drawn one again. Each draw call walked the item list twice, and a long display list cost time proportional to the square of its length on every run of pixels. The item loop in the DCS LCD, mono, e-paper and SDL renderers now keeps that limit as a running minimum while it walks the items once: an item above that starts further right on the row shortens the run, as before. The output is unchanged. The *_find_max_line_len() functions are removed. The scaled_cropped_image renderers also stop reducing the item width to the remaining source image, since the parser already does so. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Signed-off-by: Tom Hoenderdos <tomhoenderdos@gmail.com>
bettio
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Oct 1, 2026
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Split out of #18.
To find how far an item may draw from a pixel, every renderer called
*_find_max_line_len(), which scanned all the items above the drawn one again. Each draw call walked the item list twice, so a long display list cost time proportional to the square of its length on every run of pixels.The item loop in the DCS LCD, mono, e-paper and SDL renderers now keeps that limit as a running minimum while it walks the items once. It considers the same items as before (those above the drawn one that start further right on the row), so the output is unchanged. The
*_find_max_line_len()functions are removed.The
scaled_cropped_imagerenderers also stop reducing the item width to the remaining source image, since the parser does that since #19.Testing:
tests/items(ASan + UBSan, against AtomVM release-0.7): all 396 checks pass, including the pixel checks of images under occluding rects.🤖 Generated with Claude Code