The old requirement that multiple MetaBackgroundActor objects be
layered on top of each to produce blended backgrounds resulted in
extremely inefficient drawing since the entire framebuffer had
to be read and written multiple times.
* Replace the MetaBackground ClutterContent with a plain GObject
that serves to hold the background parameters and prerender
textures to be used to draw the background. It handles
colors, gradients, and blended images, but does not handle
vignetting
* Add vignetting to MetaBackgroundActor directly.
* Add MetaBackgroundImage and MetaBackgroundImageCache to allow
multiple MetaBackground objects to share the same images
By removing the usage of ClutterContent, the following optimizations
were easy to add:
Blending is turned off when the actor is fully opaque
Nearest-neighbour filtering is used when drawing 1:1
The GLSL vignette code is slightly improved to use a vertex shader
snippet for computing the texture coordinate => position in actor
mapping.
Use meta_actor_painting_untransformed() for MetaShapedTexture
The old check for using NEAREST by checking clutter_actor_is_in_clone_paint()
and meta_actor_is_untransformed (actor) doesn't work properly since
clutter_actor_is_in_clone_paint() does not look at ancestors of the
actor; it only applies to a direct clone of the actor. Using
meta_actor_painting_untransformed() allows us to check exactly what we
care about rather than using tricky approximations.
The painting_untransformed() function in MetaWindowGroup is useful
elsewhere, in particular if we want to check whether we can avoid
bilinear filtering when painting a texture 1:1.
