Since BlurEffect and DesaturateEffect are using the shader API
implicitly and not using ClutterShaderEffect, we need to check if the
underlying GL implementation supports the GLSL shading language and warn
if not.
We might want to switch the BlurEffect from a box-blur to a
super-sampling of the texture target, in order to make it cheap(er).
If we inherit from ShaderEffect, though, we're setting in stone the
fact that we are going to use a fragment shader for blurring.
Since there is not parametrization of the blur, the code necessary
to implement effect is pretty small, and we can use the Cogl API
directly.
Sub-classes of ShaderEffect currently have to get the handle for the
Cogl shader and call cogl_shader_source(); this makes it awkward to
implement a ShaderEffect, and it exposes handles and Cogl API that we
might want to change in the future.
We should provide a ClutterShaderEffect method that allows to (safely)
set the shader source at the right time for sub-classes to use.
A simple, GLSL shader-based blur effect.
The blur shader is taken straight from the test-shader.c interactive
test case. It's a fairly clunky, inefficient and visually incorrect
implementation of a box blur, but it's all we have right now until I
figure out a way to do multi-pass shading with the current API.
