Surprisingly, today I got Anukari running on Metal. It turned out that modifying the OpenCL code so that it could be run via OpenCL or Metal was a lot simpler than I expected. The macros are not all that complicated, and the code is certainly uglier in some places, but for the most part it's not too bad. It took me a while to figure out how Metal does indexing for kernel arguments (device memory and threadgroup memory have different index spaces, for example), but that was the worst of it.

It works well enough to pass basically all of the golden tests. Which is very surprising. Actually it fails a few, but they're the same few that the OpenCL implementation on MacOS fails -- for whatever reason they are extra sensitive to whatever differences there are between the M1 chip and my NVIDIA chip on Windows. So from an audio correctness standpoint, things seem to be working.

I don't yet have a good read on the performance. I slapped the rough draft implementation together very quickly, and didn't take the time yet to read through the memory allocation/ownership rules that Cocoa / Cocoa Touch use, which means that my implementation leaks memory like a sieve which is causing lots of issues. I suspect that there are a bunch of other small things I've done wrong that affect performance as well.

But from what I've seen so far, I don't think a straight port to Metal will automatically answer my performance prayers. I'll have to get it working properly, and then start experimenting with how I might be able to take better advantage of what Metal has to offer. And hopefully the instrumentation/profiling tools will work a lot better to help me with that.