material passes invalidating shaders too often - issue and suggestions

[pigiuz]

I'm digging a bit into materials and I'm finding out that lots of built in functions automatically invalidate shader programs.
This results in a frequent recompilation of the shaders lowering very much the fps.

what I suggest is:

• to let developers use a "manual" mode in order to recompile the shaders only if explicitly asked
• to improve the invalidation process in order to avoid the recompilation of a shader marked as invalid but with the same agal of the current one