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.
https://bugzilla.gnome.org/show_bug.cgi?id=735637
When there was no root background pixmap, we were using a 1x1 repeating
texture as a simple way of drawing a solid color without adding a
second code path. However, when that 1x1 texture was combined into
a larger "atlas texture", hardware repeat couldn't be used, so a
small inefficiency from this approach became an enormous inefficiency
as clutter drew every pixel of the background as a separate rectangle.
https://bugzilla.gnome.org/show_bug.cgi?id=652507
Create new cogl-utils.[ch] and move a helper function from
MetaShadowFactory there as meta_create_texture_material(); this
allows us to create single-layer materials from different parts of
Mutter and have them share the same template material.
Also expose a function for creating a 1x1 texture of a given
color meta_create_color_texture_4ub().
https://bugzilla.gnome.org/show_bug.cgi?id=634833
