Fix image plotting in Cairo backends

[jenshnielsen]

WIP solution to #6562

Call cairo.ImageSurface.create_for_data with an array that both py2cairo and cairocffi knows how to get a pointer too and size of.

This seems to correctly resolve the issue for the Cairo backend but not the GTK(3)Cairo backends.

Current status

• Python2.7, Cairo backend, cairocffi
• Python2.7, Cairo backend, py2cairo
• Python3.5, Cairo backend, cairocffi
• Python2.7, GTKCairo backend, cairocffi
• Python2.7, GTKCairo backend, py2cairo
• Python2.7, GTK3Cairo backend, cairocffi
• Python2.7, GTK3Cairo backend, py2cairo
• Python3.5, GTK3Cairo backend, cairocffi
• Python3.5, Cairo backend, py3cairo non functional with latests release of py3cairo
• Python3.5, GTKCairo backend, cairocffi python 3 NOT Supported by GTK2
• Python3.5, GTKCairo backend, py3cairo python 3 NOT Supported by GTK2
• Python3.5, GTK3Cairo backend, py3cairo non functional with latests release of py3cairo

[jenshnielsen]

More testing. Cairocffi works correctly with GTK3 if py2/3cairo is installed but not otherwise. This is probably just a concequense of the fact that gtk/pygobject is build against py2/3cairo so it can't function without.

The gtk2 backend however breaks if Cairocffi is installed

[jenshnielsen]

The issue with cairocffi and GKT2 is not new and can be reproduced on 1.5.x

Traceback (most recent call last):
  File "/usr/local/lib/python2.7/site-packages/matplotlib/backends/backend_gtk.py", line 438, in expose_event
    self._render_figure(self._pixmap, w, h)
  File "/usr/local/lib/python2.7/site-packages/matplotlib/backends/backend_gtk.py", line 426, in _render_figure
    self.figure.draw (self._renderer)
  File "/usr/local/lib/python2.7/site-packages/matplotlib/artist.py", line 62, in draw_wrapper
    draw(artist, renderer, *args, **kwargs)
  File "/usr/local/lib/python2.7/site-packages/matplotlib/figure.py", line 1159, in draw
    func(*args)
  File "/usr/local/lib/python2.7/site-packages/matplotlib/artist.py", line 62, in draw_wrapper
    draw(artist, renderer, *args, **kwargs)
  File "/usr/local/lib/python2.7/site-packages/matplotlib/axes/_base.py", line 2319, in draw
    a.draw(renderer)
  File "/usr/local/lib/python2.7/site-packages/matplotlib/artist.py", line 62, in draw_wrapper
    draw(artist, renderer, *args, **kwargs)
  File "/usr/local/lib/python2.7/site-packages/matplotlib/image.py", line 394, in draw
    renderer.draw_image(gc, l, b, im)
  File "/usr/local/lib/python2.7/site-packages/matplotlib/backends/backend_cairo.py", line 181, in draw_image
    ctx.set_source_surface (surface, x, y)
TypeError: must be cairo.Surface, not ImageSurface

[QuLogic]

Can I close #6562 then?

[tacaswell]

@QuLogic Can you do the 2.x into master merge?

[QuLogic]

Neither commit message indicates it should be closed, so that did nothing. But I ask because there are some items unchecked here...

[tacaswell]

oh, yes, close this. We decided that those platforms are not a) already broken on 1.5 and b) old c) otherwise non-functional