Re: Looking for colourful advice

[Owen Taylor <otaylor redhat com>]

On Tue, 2010-03-09 at 01:03 +0100, Florian Scandella wrote:
> couldn't one just write a custom shader and set it for an actor? or is
> the clutter shader api not supported by gnome-shell?

 - GLSL shaders (the ones that Clutter has support for) aren't available
   on all hardware.

 - Pixel shaders only are used to determine the color of the "fragment"
   - the color that will be combined with the existing color in the
   frame buffer. The combination process itself isn't within the
   scope of the shader.

   So, to get the effect that Joseph is looking for with a shader,
   you'd have to copy the area under the cross-hairs from the frame
   buffer into a temporary buffer, invert that in the shader and
   then the write the result back.

   Using glLogicOp should be a lot simpler and more efficient.

   (On the other hand, some other desired effects for magnification
   would be best done with a shader, and likely will involve rendering
   the magnified area directly to an offscreen buffer.)

- Owen