Stripey `LineCollection` #24849

rcomer · 2022-12-31T10:19:18Z

PR Summary

Following #23208, which implemented the gapcolor property for Line2D, this PR implements gapcolor for LineCollection. So we can set a colour (or list of colours) to fill the gaps in dashed lines and make a striped effect. For example

import matplotlib.pyplot as plt

_, ax = plt.subplots()
ax.vlines(range(1, 5), 0, 1, linestyle=':', linewidth=5,
          color='k', gapcolor=['r', 'b'])

plt.show()

I marked this functionality as "experimental" to be consistent with Line2D.

My current implementation works, but I'm pretty unsure about the way I've structured it: it doesn't seem great to have the LineCollection-specific handling within Collection. The only way I can see to avoid that is to define LineCollection.draw, but that would mean duplicating some code, which also wouldn't seem great.

For reference, the test images look like this:

gapcolor='orange'

gapcolor=['r', 'k']

I'm happy to squash the commits down once we're happy with the implementation, but I suspect there will be plenty of changes before that...

PR Checklist

Documentation and Tests

Has pytest style unit tests (and pytest passes)
Documentation is sphinx and numpydoc compliant (the docs should build without error).
New plotting related features are documented with examples.

Release Notes

New features are marked with a .. versionadded:: directive in the docstring and documented in doc/users/next_whats_new/
[N/A] API changes are marked with a .. versionchanged:: directive in the docstring and documented in doc/api/next_api_changes/
Release notes conform with instructions in next_whats_new/README.rst or next_api_changes/README.rst

rcomer · 2022-12-31T12:41:06Z

lib/matplotlib/collections.py

@@ -406,6 +410,17 @@ def draw(self, renderer):
                gc, paths[0], combined_transform.frozen(),
                mpath.Path(offsets), offset_trf, tuple(facecolors[0]))
        else:
+            if self._gapcolor is not None:


Note that do_single_path_optimization is only True if all the lines are solid

matplotlib/lib/matplotlib/collections.py

Line 381 in fc5d316

all(ls[1] is None for ls in self._linestyles) and

so gapcolor is only meaningful after this else.

jklymak · 2023-02-02T17:08:49Z

@rcomer for a new feature like this, its nice to either include example code in the description, or in documentation of the feature. I'm not quite following the API from the test images and the tests (though I only tried for a minute or so).

rcomer · 2023-02-03T10:11:24Z

Thanks @jklymak, I have updated the OP.

jklymak · 2023-02-08T00:33:03Z

@timhoffm @oscargus you reviewed the original feature for Line2d. Does this seem reasonable here?

jklymak

This seems fine to me, despite never using v/hlines ;-)

story645

Wording nits but I'm happy w/this. Thanks! (Also sorry for dragging this into the color validation arguments)

story645 · 2023-01-15T20:53:03Z

lib/matplotlib/collections.py

+            There can be overlaps between those two, which may result in
+            artifacts when using transparency.
+
+            This functionality is experimental and may change.


smallest little nit but I'd put only this very last sentence in the note and have everything else as just part of the docstring.

The note here was lifted straight from the equivalent in Line2D.
https://matplotlib.org/stable/api/_as_gen/matplotlib.lines.Line2D.html#matplotlib.lines.Line2D.set_gapcolor

I think it should be changed there too but out of scope so I can put in that PR

From what I remember of #23208, this went through a few iterations: started out with a warning about overlaps that don't look great with transparency. Then the warning was downgraded to a note, and the "experimental" bit added later. Given the amount of previous bikeshedding on this, I would be uncomfortable about changing it without a bit more discussion. That could happen in a follow-up PR, as you say.

story645 · 2023-02-08T16:21:19Z

lib/matplotlib/collections.py

+        Used when gapcolor is set.  Return the path and inverse pattern for
+        non solid lines, so we can use these to fill the gaps.  For solid lines
+        we insert a path of nans so that no inverse line is drawn in that case.


Suggested change

Used when gapcolor is set. Return the path and inverse pattern for

non solid lines, so we can use these to fill the gaps. For solid lines

we insert a path of nans so that no inverse line is drawn in that case.

Returns the path and pattern for the gaps in the non-solid lines.

This path and pattern is the inverse of the path and pattern used to construct the non-solid lines. For solid lines, we set the inverse path to nans to prevent drawing an inverse line.

Wordsmithing, take or leave

story645 · 2023-02-08T16:22:35Z

lib/matplotlib/collections.py

+        non solid lines, so we can use these to fill the gaps.  For solid lines
+        we insert a path of nans so that no inverse line is drawn in that case.
+        """
+        pairs = [


Pairs is path_pattern?

Do you mean I should change the variable name? Happy to do so if so.

Was confirming that I understood what the code was doing but if I'm right than yes please

rcomer · 2023-02-10T19:00:02Z

Does anyone have an opinion on this Codecov failure? It seems unlikely to me that such a simple method could get broken.

jklymak · 2023-02-11T23:30:01Z

Thanks @rcomer !

rcomer · 2023-02-12T09:40:52Z

Thanks @jklymak, @story645 - this one was considerably more straightforward than I feared!

rcomer added API: consistency topic: collections and mappables labels Dec 31, 2022

rcomer commented Dec 31, 2022

View reviewed changes

QuLogic added the New feature label Jan 1, 2023

story645 added this to the v3.8.0 milestone Jan 5, 2023

story645 mentioned this pull request Jan 16, 2023

[MNT]: _check_color_like for list like input #25005

Closed

story645 mentioned this pull request Jan 26, 2023

_check_color_like function for list inputs #25025

Closed

3 tasks

rcomer added the status: needs clarification Issues that need more information to resolve. label Feb 2, 2023

rcomer removed the status: needs clarification Issues that need more information to resolve. label Feb 3, 2023

jklymak approved these changes Feb 8, 2023

View reviewed changes

story645 approved these changes Feb 8, 2023

View reviewed changes

ENH: gapcolor for LineCollection

3b4bd83

rcomer force-pushed the stripey-line-collection branch from 4f872b9 to 3b4bd83 Compare February 9, 2023 19:22

story645 approved these changes Feb 9, 2023

View reviewed changes

jklymak merged commit 81f5f24 into matplotlib:main Feb 11, 2023

rcomer deleted the stripey-line-collection branch February 12, 2023 13:28

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Stripey `LineCollection` #24849

Stripey `LineCollection` #24849

rcomer commented Dec 31, 2022 •

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rcomer commented Feb 12, 2023

Stripey LineCollection #24849

Stripey LineCollection #24849

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rcomer commented Feb 10, 2023

jklymak commented Feb 11, 2023

rcomer commented Feb 12, 2023

Stripey `LineCollection` #24849

Stripey `LineCollection` #24849

rcomer commented Dec 31, 2022 •

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story645 Feb 8, 2023 •

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