Supporting different alphas for face and edge colours #1954

Westacular · 2013-04-27T22:14:01Z

This is a set of changes that solve the issues raised by #1899 and #1938.

Linestyles

Ignore what I said before in #1899 about linestyles.

Turns out it was working correctly for patches, but the dashes and dots were all overlapping at linewidth=5. The culprit is a single line in Patch.draw() that was setting the gc to use 'projecting' capstyle. This capstyle causes the rendered length of dashes and dots to increase in proportion to the width, however, the spacing between them (which ignores the caps) remains constant. At linewidth=5 the spaces are completely covered by the caps, making it look like linestyle='solid'.

Letting capstyle='butt', the default, fixes this.

(Also, there was a bug in the PGF backend that was causing Collections (or anything with a custom dash pattern) to always use a solid linestyle. Fixed that.)

Also, for some reason, in the SVG header stroke-linecap:square(the translation of capstyle='projecting') was being set as the default, even though the default for most objects is butt. This was causing a problem with the rendering of the PathCollection, because (at least on WebKit) the style for the collection, which did specify butt, was not overriding that default. The net effect was the same as the above problem for patches.

Mixed Edge and Face Alpha Values

There was already stubs of logic (and a _forced_alpha attribute of GraphicsContext) for the notion that if an explicit alpha is set (through gc.set_alpha()) it should override any face and edge alphas, but otherwise, leave them be; however, it was largely ignored by most backends, each of which tended to do its own slightly different thing with regard which it recognized and how it handled them.

I've updated (and tested to varying degrees) the AGG, PDF, SVG, PGF, Mac OS X, and Cairo backends, along with various fixes to the backend bases and to the Patch class. As far as I can tell, that covers everything that's already paying attention to the gc.get_alpha() value.

I also fixed the bug (also discussed at #1938) where setting an alpha value on the patch would override edgecolor='none'. The new behaviour is that the value given to alpha is ignored by the edge colour if and only if edgecolor='none' exactly; edgecolor=(x,x,x,0) still gets overridden by alpha. This is the existing behaviour for facecolor, which I've not changed.

I've included the test (and changes) added by @pelson in #1899, along with correct results, and corrected the results of the clip_to_bbox test (which were previously affected by the alpha=x/edgecolor='none' bug). I've also added another test to check that the alpha attribute is overriding the alpha components of the face and edge colors.

pelson · 2013-04-29T09:12:21Z

The test results are looking good - there is a lot of change here which needs to be considered, but I'd like to target this for v1.3.

Amazing work @Westacular.

Westacular · 2013-04-29T21:02:47Z

Thanks.

Just noticed the Travis build had failed. I didn't have inkscape installed, so I didn't notice there was a regression with SVG in my own testing. I've since fixed the problem (hatches were not having their alpha applied in SVGs).

pelson · 2013-05-01T13:46:47Z

I didn't have inkscape installed, so I didn't notice there was a regression with SVG in my own testing. I've since fixed the problem (hatches were not having their alpha applied in SVGs).

Wooho! Travis caught a genuine problem! 😄

mdboom · 2013-05-03T14:25:33Z

@Westacular: Would you mind rebasing this on current master so that this will merge cleanly and the tests will run again?

…enough

…ll be rendered as black. Also fixes test case result that hit this bug

Specifically, alters the base, AGG, PDF, PGF, SVG, Cairo, and Mac OS X backends to better enable the use of RGBA color values for both fills and edges. An explicit alpha attribute, if set, will override the alpha channels of the color values. Updates test results, which are now what would be expected. Also fixes a couple bugs with handling of linestyles.

Westacular · 2013-05-03T16:10:10Z

@Westacular: Would you mind rebasing this on current master so that this will merge cleanly and the tests will run again?

Done. (Also squashed some of the commits, where it made sense.)

mdboom · 2013-05-03T16:14:15Z

lib/matplotlib/backends/backend_svg.py

@@ -289,7 +289,7 @@ def _write_default_style(self):
        writer = self.writer
        default_style = generate_css({
            u'stroke-linejoin': u'round',
-            u'stroke-linecap': u'square'})
+            u'stroke-linecap': u'butt'})


Good catch -- indeed the "default" according to the SVG spec is butt.

mdboom · 2013-05-03T16:16:32Z

Thanks for all of this work. It looks great. I think it's significant enough that it should have an entry in what's new -- and perhaps in API changes, if there's a way of summarizing changes in behavior between old and new (even though old was obviously broken)...

pelson · 2013-05-03T16:38:12Z

and perhaps in API changes

Definately.

pelson · 2013-05-03T16:41:24Z

lib/matplotlib/backend_bases.py

            self._rgb = fg
        else:
            self._rgb = colors.colorConverter.to_rgba(fg)
-        if len(self._rgb) == 4 and not self._forced_alpha:
-            self.set_alpha(self._rgb[3])


This is subtle, but I think it will break the non forced alpha case.

Question: Should calling set_alpha turn on the forced_alpha value?

set_alpha does turn on _force_alpha -- in fact, it already did, I didn't need to change anything there. (But prior these changes, practically nothing actually paid attention to it.) Calling gc.set_alpha(None) clears _forced_alpha.

This doesn't break the non-forced alpha case because the backends themselves, where appropriate, now pull the alpha value straight out of _rgb[3] in the non forced alpha case.

Westacular · 2013-05-04T20:32:16Z

Thanks for all of this work. It looks great. I think it's significant enough that it should have an entry in what's new -- and perhaps in API changes, if there's a way of summarizing changes in behavior between old and new (even though old was obviously broken)...

Happy to help. I took a crack a explaining the high-level/user-facing changes, while omitting the finer details of other bugs that were fixed or how backends were changed. Let me know what you think.

pelson · 2013-05-07T11:21:11Z

doc/api/api_changes.rst

+  :class:`~matplotlib.patches.Patch` had ``alpha=None``, the alpha component
+  of ``edgecolor`` would be applied to both the edge and face.
+
+* For :class:`~matplotlib.patches.Patch`, the ``capstyle`` used is now


This is SVG only, right?

pelson · 2013-05-07T11:27:40Z

I see this as the "open heart surgery" of v1.3 (@mdboom's terminology used for a PR of mine on transforms in v1.2). I think on the whole the behaviour is more consistent, expected and desirable as a result of this PR, and it is for that reason (and the thoroughness of @Westacular's work) that I'd be comfortable merging this.

👍 - awesome work @Westacular!

mdboom · 2013-05-07T12:53:46Z

Agreed! Awesome work!

I know this issue has been brought up by @efiring a number of times over the years, so I thought I'd give him the opportunity to comment before merging, just in case there's anything additional.

efiring · 2013-05-07T17:29:25Z

I'm happy to see this.

There is one change in the formally public API that could be mentioned in API_CHANGES: in GraphicsContext*.set_foreground, the isRGB kwarg is now isRGBA. I think the change is fine, and it is unlikely that user code is calling this low-level method directly, so I don't think a deprecation process is needed.

Westacular · 2013-05-08T02:48:52Z

Ok, I've added a note about the isRGBA change.

Thanks for the kind words... And thanks for trusting me with the scalpel. :)

Supporting different alphas for face and edge colours

Westacular mentioned this pull request Apr 27, 2013

Updated patch to not override alpha on edgecolor if set to none #1938

Closed

pelson and others added 5 commits May 3, 2013 11:51

Failing tests.

ae5c2f1

Fixes bug where linestyle always appears solid if linewidth is large …

1e7399f

…enough

Fixes bug where if alpha is set and edgecolor='none', edges would sti…

1aefc52

…ll be rendered as black. Also fixes test case result that hit this bug

Add additional patch tests.

a7f7cc7

mdboom reviewed May 3, 2013
View reviewed changes

pelson reviewed May 3, 2013
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Westacular added 2 commits May 4, 2013 16:18

Added documentation of patch/alpha changes.

cd18645

Another documentation update

71e9ad9

pelson reviewed May 7, 2013
View reviewed changes

Documenting the isRGB -> isRGBA change to API

ba1f673

efiring added a commit that referenced this pull request May 11, 2013

Merge pull request #1954 from Westacular/alpha-patch

60e67e0

Supporting different alphas for face and edge colours

efiring merged commit 60e67e0 into matplotlib:master May 11, 2013

efiring mentioned this pull request May 11, 2013

Different alphas for lines and fills. #1899

Closed

pelson mentioned this pull request Oct 9, 2013

Rastized background color #2479

Merged

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Supporting different alphas for face and edge colours #1954

Supporting different alphas for face and edge colours #1954

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Conversation

Westacular commented Apr 27, 2013

Linestyles

Mixed Edge and Face Alpha Values

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pelson commented Apr 29, 2013

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Westacular commented Apr 29, 2013

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pelson commented May 1, 2013

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mdboom commented May 3, 2013

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Westacular commented May 4, 2013

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Westacular commented May 8, 2013

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