Andre Duvoisin

Metal is missing a lot of essential functionality, and it's hostile toward cross-platform development.

The minimum that I would need to even consider the Mac again is: * C API. * Shading language that supports standard syntax in GLSL/HLSL/PSSL/Cg. * Depth bounds test. * Timer queries (with same granularity as OpenGL). * Geometry shaders. (Not used much, but needed. No emulation.)

* "Standard syntax" - do you mean you want to use GLSL/HLSL/PSSL/Cg verbatim? * What do you expect a GL style timer query to do on a TBDR architecture? * What important use cases are you using geometry shaders for?

For the shader syntax, here are a couple examples. These are just meant to demonstrate how Metal introduces unnecessary friction for cross-platform development.

If I want an output parameter on a function, I simply declare it ‘out’ in GLSL, HLSL, and PSSL: void func(out float param) In Metal, I have to write it like this: void func(thread float& param) The Mac requires special-case code that no other platform needs.

In GLSL, HLSL, and PSSL, the functions that fetch an unfiltered texel all take signed integer coordinates. But in Metal, the equivalent function takes unsigned integer coordinates. Again, the Mac requires special-case code for absolutely no benefit.

The biggest problem with Metal shading language is the lack of global resources (textures, buffers). You need to give all resources as function params to main function and pass them around to every utility function. This is incompatible with text based shader node graph splicing.

Then there's the MSL atomics. If you want to do atomics to groupshared memory buffer, you need to change type to atomic<T> and simple stuff like assignment doesn't work anymore. Need to use atomic load/store instead. Need to wrap these to macros on every platform :(