[ New 28/02/2017 :  WebGL2.0 compatibility issues. See last section. ] Sometimes, somebody else shader looks strange, or blank, or broken, on your machine. Conversely, if your shader works on your machine, it's not a proof that it works elsewhere. Usual suspects: Noisy image:  - Variable not initialized. Blank image:  - Negative parameter for log, sqrt, pow.  …