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Make sure custom alpha param does not change 'none' colors in a list of colors #27845

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Merged
merged 2 commits into from
Mar 9, 2024
Merged

Make sure custom alpha param does not change 'none' colors in a list of colors #27845

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c3b182e
fix issue 27839, make sure alpha param does not affect none colors
chaoyihu Mar 3, 2024
193acbc
Update lib/matplotlib/colors.py
timhoffm Mar 8, 2024
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5 changes: 5 additions & 0 deletions lib/matplotlib/colors.py
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Original file line number Diff line number Diff line change
Expand Up @@ -506,6 +506,11 @@ def to_rgba_array(c, alpha=None):

if alpha is not None:
rgba[:, 3] = alpha
if isinstance(c, Sequence):
# ensure that an explicit alpha does not overwrite full transparency
# for "none"
none_mask = [cbook._str_equal(cc, "none") for cc in c]
rgba[:, 3][none_mask] = 0
return rgba


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11 changes: 11 additions & 0 deletions lib/matplotlib/tests/test_colors.py
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Expand Up @@ -19,6 +19,7 @@
import matplotlib.scale as mscale
from matplotlib.rcsetup import cycler
from matplotlib.testing.decorators import image_comparison, check_figures_equal
from matplotlib.colors import to_rgba_array


@pytest.mark.parametrize('N, result', [
Expand Down Expand Up @@ -1660,3 +1661,13 @@ def test_set_cmap_mismatched_name():
cmap_returned = plt.get_cmap("wrong-cmap")
assert cmap_returned == cmap
assert cmap_returned.name == "wrong-cmap"


def test_to_rgba_array_none_color_with_alpha_param():
# effective alpha for color "none" must always be 0 to achieve a vanishing color
# even explicit alpha must be ignored
c = ["blue", "none"]
alpha = [1, 1]
assert_array_equal(
to_rgba_array(c, alpha), [[0., 0., 1., 1.], [0., 0., 0., 0.]]
)