GLMixer Code

BIG RE-DESIGN; in order to improve performances, the rendering of every sources (loop over all video textures) is now done ONCE, and the mixing rexult is rendered on the fly into an FBO. This FBO is then displayed as a simple texture in the OutputRenderWindow (which is extremely fast, even more with the FBO blit GL extension). To makes things simpler, the RenderingManager is now dealing with the rendering and the sources, and the views are only procedures used to know how to show the manipulation view.