So I was wondering what the state of play is regarding multiple render targets. I understand that they're in the 1.0 specification, but due to lack of ubiquitous hardware support (as in the case of mobile) it's not implemented anywhere. Is my understanding correct?
MRTs are not in the WebGL 1.x specifications.
The basics first, MRTs are defined across three desktop OpenGL extensions:
OpenGL ES defines some MRT extensions:
The (WebGL) powers that be decided that WebGL cannot obtain desktop only graphics features. And since mobiles only support MRTs for Nvidia (and not for Apple as well), WebGL cannot have MRTs.
I don't know if the PowerVR chipset family that Apple uses are MRT capable at all (but I suspect they are). I also don't know why an OES_DRAW_BUFFERS hasn't been added to the OpenGL ES extension registry.