Since _cogl_pipeline_update_blend_enable() can sometimes show up quite
high in profiles; instead of calling
_cogl_pipeline_update_blend_enable() whenever we change pipeline state
that may affect blending we now just set a dirty flag and when we flush
a pipeline we check this dirty flag and lazily calculate whether blender
really needs to be enabled if it's set.
Since it turns out we were too optimistic in assuming most GL drivers
would recognize blending with ADD(src,0) is equivalent to disabling
GL_BLEND we now check this case ourselves so we can always explicitly
disable GL_BLEND if we know we don't need blending.
This introduces the idea of an 'unknown_color_alpha' boolean to the
pipeline flush code which is set whenever we can't guarantee that the
color attribute is opaque. For example this is set whenever a user
specifies a color attribute with 4 components when drawing a primitive.
This boolean needs to be cached along with every pipeline because
pipeline::real_blend_enabled depends on this and so we need to also call
_cogl_pipeline_update_blend_enable() if the status of this changes.
Incidentally with this patch we now no longer ever use
_cogl_pipeline_set_blend_enable() internally. For now the internal api
hasn't been removed though since we might want to consider re-purposing
it as a public api since it will now not conflict with our own internal
state tracking and could provide a more convenient way to disable
blending than setting a blend string.
Reviewed-by: Neil Roberts <neil@linux.intel.com>
(cherry picked from commit ab2ae18f3207514c91fa6fd9f2d3f2ed93a86497)
8f9151303d