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gtk3cairo draw_image does not respect origin and mishandles alpha #8798
Description
As of master (and probably since a long time)
from pylab import *
rcdefaults()
fig, axs = plt.subplots(1, 2)
axs[0].imshow(np.arange(4).reshape((2, 2)))
axs[1].imshow(np.arange(4).reshape((2, 2)), alpha=.5)
show()
produces, on gtk3agg
and on gtk3cairo
Looks like image.origin is not respected, and alpha is not applied correctly (this is not surprising, as cairo uses premultiplied ARGB (https://www.cairographics.org/manual/cairo-Image-Surfaces.html#cairo-format-t CAIRO_FORMAT_ARGB32).
Activity
AlexanderLarsRobinson commentedon Jul 17, 2017
I'd like to comment that using the
imshowargumentorigin = 'lower'will still flip the image upside-down fromorigin = 'upper', thus leaving the drawn image consistently inverted relative to Matplotlib's coordinates with this backend.This caused me some confusion last week, so I'm glad I'm not the first to notice it.
AlexanderLarsRobinson commentedon Jul 18, 2017
Looking more closely at older issues, the inversion thing seems to be a thing that has come and gone at least once already ...
anntzer commentedon Jul 18, 2017
I consider the current cairo backend broken beyond repair.
If you are interested in using cairo, please have a look at https://github.com/anntzer/mpl_cairo, which can fully replace Agg. I would gladly accept any help in getting that backend packageable/ PR'able into the main repo.