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Fix Collection.draw() single-path optimization when edgecolor/facecolor is 'none' - #32232

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Fix Collection.draw() single-path optimization when edgecolor/facecolor is 'none'#32232
ayshih wants to merge 1 commit into
matplotlib:mainfrom
ayshih:path_optimization_color_none

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@ayshih

@ayshih ayshih commented Aug 19, 2026 •
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PR summary

Fixes #17790. The immediate bug is that setting facecolor or edgecolor to "none" sets the color to an empty list, but the Collection.draw() logic to detect for single-path optimization does not consider an empty list to be a single color. That is, single-path optimization would never happen if facecolor or edgecolor is set to "none". This PR fixes that situation.

That said, this PR requires discussion because single-path optimization is newly triggered in 30+ figure tests, which means their baseline images need to be updated. This is because draw_markers() produces different output than draw_path_collection(). It's worth investigating whether single-path optimization is in fact appropriate in all cases before accepting this PR.

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PR quality check

  • Use an expressive title, e.g. "Fix title font property precedence"
  • New and changed code is tested
  • [N/A] Plotting related features are demonstrated in an example
  • [N/A] New features and API changes have release notes
  • [N/A] Documentation complies with general and docstring guidelines

This was referenced Aug 19, 2026
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ayshih force-pushed the path_optimization_color_none branch from 571623a to 1d57e2b Compare August 19, 2026 15:44
@ayshih

ayshih commented Aug 20, 2026

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That said, this PR requires discussion because single-path optimization is newly triggered in 30+ figure tests, which means their baseline images need to be updated. This is because draw_markers() produces different output than draw_path_collection(). It's worth investigating whether single-path optimization is in fact appropriate in all cases before accepting this PR.

  • We could reduce the number of images affected by this PR by creating a way to disable single-path optimization where it is not appropriate given the collection type.
  • We could review the (Agg) code for draw_markers() and draw_path_collection() to see if there are any bugs that are contributing to the discrepancies between the rendered output.

@QuLogic

QuLogic commented Aug 20, 2026

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There's been a long standing bug with the single-path optimization #15946 Possibly #32108 may be relevant here, though I didn't test that specific case yet.

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Successfully merging this pull request may close these issues.

Using facecolors='none' with a scatter plot results in off-centered symbols

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