This also switches the rendering code from using gsk_render_node_draw()
to gsk_renderer_render_texture().
Some tests are broken with the GL renderer, so this patch forces the
Cairo renderer until they get fixed.
If the alpha channel is zero, it doesn't matter what the values of the
red, green and blue channels are: the pixel is still fully transparent.
On most architectures, fully transparent pixels end up all-zeroes
(fully transparent black), matching what's in the reference PNG file;
but on mips*el the blend-difference and blend-normal tests get all-ones
(fully transparent white) and a test failure.
Resolves: https://gitlab.gnome.org/GNOME/gtk/-/issues/4227
Signed-off-by: Simon McVittie <smcv@debian.org>
This is the only non-whitespace difference between the copies in
testsuite/reftests/ and testsuite/gsk/.
Signed-off-by: Simon McVittie <smcv@debian.org>
