Adds a FXAA for smoothing out the extracted outlines.
The Post Process Anti Aliasing is only done on the Alpha channel of the outlines.
Because of that we need to add bleed the outline color out of the silouhette so the AA'd alpha can blend the right color and not pick black when the alpha is smoothed out of the silhouette.
Also because of the AA needs to have clear contrast to work with, I decided to ditch the "bluring" or the occluded outlines.
The FXAA adds an overhead of 0.17ms but we gain back 0.22ms * 4 = 0.88ms by removing the blur.
The FXAA Implementation is from Corey Richardson (cmr) (D2717). I had to modify it a bit to only filter the alpha channel.
We render selected meshes into another buffer and use a screen space shader to expand the color out of the mesh silouhette.
Pros: only one additionnal render pass is needed (like old outline code), and we have occluded informations.
Cons: memory usage is a problem. This method needs 2 color buffer to ping pong when expanding the outline and 1 depth buffer to test occluded fragments. This gives a 88 bits/pix memory footprint.
Idea: Since we don't need all color range but only some uniform colors (theme colors) we could manipulate only the color ID instead of the whole color this could cut the color buffer size and lower the memory footprint to 58 bits/pix.
