Snap markers to subpixels instead of whole ones#32108
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We cache the marker for performance, but this causes it to look very pixel-grid aligned, especially if there are multiple in a regular pattern, or they are animated. Apply the same algorithm as mplcairo noted by @anntzer in matplotlib#7233, specifically, render and cache the marker in *n_subdiv* levels in each direction, and pick the closest one for each marker. Fixes matplotlib#7233
QuLogic
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Jul 23, 2026
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| // TODO: Pixel markers *must* be drawn snapped. | ||
| auto const& is_pixel_marker = false; | ||
| // py_eq(marker_path, PIXEL_MARKER.attr("get_path")()) | ||
| // && marker_trans == PIXEL_MARKER.attr("get_transform")().cast<agg::trans_affine>(); |
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mplcairo special-cases the pixel marker; I have not checked how that turns out or whether that is necessary.
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| auto marker_path_snapped = PathSnapper{ | ||
| marker_path_nan_removed, | ||
| gc.snap_mode, marker_path.total_vertices(), | ||
| points_to_pixels(gc.linewidth)}; |
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I'm not 100% certain we should be snapping here for each of the cached subpixel markers. It affects a lot more test images if we drop this though.
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The original issue with current style looks like this: |
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PR summary
We cache the marker for performance, but this causes it to look very pixel-grid aligned, especially if there are multiple in a regular pattern, or they are animated.
Apply the same algorithm as mplcairo noted by @anntzer in #7233, specifically, render and cache the marker in n_subdiv levels in each direction, and pick the closest one for each marker.
Fixes #7233
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