This test assumes that the textures will be stored internally with exactly
the color given so that specific texture combining arithmetic can be
tested. Using COGL_PIXEL_FORMAT_ANY allows Cogl to internally premultiply
the textures, so we have to explicitly request an unmultiplied format.
The test was quiting after the 2nd frame but it should be the third frame because
the test doesn't actually check results until the third frame due to the workaround
for drivers with broken glReadPixels.
(When first written the test would have been verified with the
clutter_main_quit() commented out which gives visual feedback of what the
test does, so the off by one would have snuck in just before uncommenting
and pushing.)
Setting up layer combine functions and blend modes is very awkward to do
programatically. This adds a parser for string based descriptions which are
more consise and readable.
E.g. a material layer combine function could now be given as:
"RGBA = ADD (TEXTURE[A], PREVIOUS[RGB])"
or
"RGB = REPLACE (PREVIOUS)"
"A = MODULATE (PREVIOUS, TEXTURE)"
The simple syntax and grammar are only designed to expose standard fixed
function hardware, more advanced combining must be done with shaders.
This includes standalone documentation of blend strings covering the aspects
that are common to blending and texture combining, and adds documentation
with examples specific to the new cogl_material_set_blend() and
cogl_material_layer_set_combine() functions.
Note: The hope is to remove the now redundant bits of the material API
before 1.0
