Actors Blending.

[Jamil Drareni <urbeller gmail com>]

Hi,

I would like to blend actors like we would do it with OpenGL 
(glBlendFunc) or Photoshop (using a pixel wise equation).
After digging into clutter's source/doc I came up with to hints:

1/ Re-implement ClutterImage so I can call cogl pipeline blend strings.
2/ Using a ClutterShaderEffect and coding the appropriate blend equation.

In the first case, the blend functions are limited.

Using a shader is more versatile but  I can't figure out a way to expose 
to a shader
, running on an actor, the texture of a previously rendered actor (a 
sibling actor for instance).

Thank you,