OpenGL / Metal shader differences

@Simeon @John since you plan to migrate the runtime from OpenGL to Metal, does this mean shader syntax will change as well?

@se24vad I think there will be, but the method @John has been going with for the new engine is to transpile GLSL code into Metal shader code

It might be hard to support features like the Shader Lab with the new engine, so we will look at tighter integration between Shade and Codea instead

@se24vad Ultimately there isn’t a practical way to make the new engine shaders 100% compatible. That said I’m working to make sure GLSL-like shaders will work even if there are some differences.