Add 2 new shaders:
* ps_main12: cast a 16 bit depth to a RGB5A1 color
* ps_main16: cast a a RGB5A1 color to a 16 bit depth
Shader might be used in future commit as it seems Silent Hill uses this
kind of format.
Fix tab/indentation too
The purpose is to avoid issue on MS-Intel driver without
a dedicated hack in the compilation.
Code doesn't use it so I suspect others implement to discard the
statement.
It might save a couple of fps
Add a define to test the perf if we keep only the blue channel. It brokes
the code in Prince Of Persia that use the Red/Green channel... Maybe the
speed hack :( Or find a way to replace all if with a lookup table
Note: it is only supported on OpenGL currently
Still not yet enabled by default
Potentially it can be optimized with the dot product but special care
need to be taken to ensure float accuracy.
Bonus: it could work on old GPU (aka DX9)
Gregory Hainaut