Wat.

Metal and OpenGL two completely different APIs, shading languages and probably a whole host of other things.

I've ported my fair share of things from fixed-function to programmable shader pipelines and you'd be effing naive if you think you can do that in a couple weeks on anything more than a toy demo.

I worked with a AAA gamedev recently who had written a Vulkan renderer for their game to demo quality level in 2 weeks. It all depends on existing level of abstraction for the rendering API and shading language (and to some extent assets), and how much performance and efficiency you’re happy leaving on the table.

> demo quality level in 2 weeks

Getting pixels on the screen and shipping something to end users are to very, very different things, 90/10 rule and all that.

Vulkan also has the benefit of multiple platforms supporting it so you're not doing all that work for a minority(which is what OSX is in the graphics space) platform.

If you already had an architecture with replaceable renderers, especially with DirectX 12 one already written, adding Vulkan one will be a matter of just a few weeks. If you hadn't, it will be much tougher.

Well Modo isn’t a toy.

The question is, how many devs did they have working those two weeks (and what resources did Apple provide to help them)?

I develop an OpenGL-based video engine for a live media playback application, which is very nearly as simple an application of OpenGL as you can expect to find in the real world, and there's no way I could expect to port it to Metal in a week or two singlehandedly. Like others have mentioned, it's a completely different paradigm, not just a matter of changing around some function calls.

That said, I welcome this change with open arms (and secure in the knowledge that legacy code will continue to work for the foreseeable future). OpenGL is a fragmented, brittle, spaghetti-inducing pile of global state. Rewriting in Metal isn't anywhere near as small a project as Apple claims, but I'm perversely looking forward to it -- I'll be very happy to have OpenGL in my rearview mirror.