For now only identity, mirror and squeeze effects are available.
Maybe some factorization is needed about compilation shader
before to put the other effects since only a copy/past is needed,
at least until effect number 9: heat.
The effects from 10:sepia to 15:glow require more work.
Add xray effect. Maps luma to a negative, slightly cyan tinted, curve,
applies some light gaussian blur and multiplies it with its sobel edges. Not
sure about the name, likely to change. Probably still needs some tuning.
