Mastodawn

aeva Mar 9, 2025

if you think about it, vulkan logical device implies the existence of vulkan illogical device

aeva Mar 9, 2025

I'm slowly working through the vulkan spec writing a compute-only vulkan program from scratch that doesn't render anything, and it's going pretty well because the spec is really well written and I already know more or less exactly what I want to do anyway, but I just want to say just how silly (fun) it feels to write a program like this because you get to just skip over large swaths of the API.

Like, I'm working from the spec because the tutorials all make it more complicated.

aeva Mar 9, 2025

also the tutorials I reviewed all did the annoying thing where the tutorial squirrels away the stuff you're trying to learn or reference into abstractions that only serve the needs of the tutorial writer, which given my goal is very specifically to *not draw anything*, there's really not much of a point to any of them lol. I'm really not the intended audience here though :3

aeva Mar 10, 2025

I think it's cute that practically every vulkan command has one or more optional args to let you enter Hard Mode

(sorry for the double post, I added this to the wrong thread)

aeva Mar 10, 2025

ok even with just the compute-only subset vulkan is a slog D:

aeva Mar 10, 2025

I wonder how many people have actually managed to knuckle down and write a complete, useful vulkan program from scratch (no copy pasting from tutorials and stack overflow, no offloading significant parts to 3rd party libraries like VMA)

To think if I power through and get this thing working I could potentially be like the 20th person to bother

aeva Mar 12, 2025

oh, update on my little vulkan compute project, last night I got as far as repeatedly dispatching an empty compute shader and allocating some memory 😎 I'm in the home stretch! I think I just need to figure out the resources / resource binding stuff and then I'll be able to start on my DSP experiment :3

which mostly means the next things are figuring out the least effort way of getting audio data into C++ (probably stb_vorbis?) and writing even more boilerplate for alsa...

aeva Mar 13, 2025

Success! I got the vulkan compute shader cranking out the fibonacci series and reading it back to the CPU through a 8 byte persistently mapped buffer. Should be smooth sailing from here.

aeva Apr 20, 2025

ok *whew* I finally did it! I implemented convolution reverb as a vulkan compute shader, and the results seem to be correct. I have it convolving the audio up front at the moment, but it seems to be reasonably fast and the results seem more or less correct. I'm using SDL3 to verify the output. It doesn't look like it'll be too crazy to rework it such that the stream is generated live.

aeva Apr 20, 2025

it turns out the main difficulty working with vulkan is accidentally breaking your laptop in half

aeva Apr 20, 2025

I reworked it so the convolution shader processes the audio in tandem with playback, so I'm *very* close to getting this working with live audio streams.

But more importantly, I used this to convolve my song "strange birds" with a choir-ish fanfare sound effect from a game I used to play as a kid and the result is like the grand cosmos opened up before me and I'm awash in the radiant light of the universe. Absolutely incredible.

aeva Apr 21, 2025

I want to power through and get this into a state where I can use it with live instruments, but I am completely exhausted 😴

aeva May 2, 2025

I reworked some things and now my audio convolving compute shader can convolve ~11 milliseconds worth of audio samples with an average processing time of ~7 milliseconds. That's with one channel with a bit rate of 22050. When the bit rate is 44100, the average processing time is a paltry ~8 milliseconds.

aeva May 2, 2025

also sometime in the last week I made it so it can operate entirely on a live input stream from SDL3 rather than a wave file, so in theory I can incorporate this into a modular setup now, but the results are higher latency than I'd like, and SDL3 doesn't give you much control over audio latency.

aeva May 2, 2025

Apparently my best frame time can get as low as 3 ms. I think vulkan should let me VK_QUEUE_GLOBAL_PRIORITY_REALTIME this program, but sadly vulkan is being a coward about it.

aeva May 2, 2025

ok the problem I'm having with latency now is that the audio latency in the system grows over time and I'm not sure why. like it starts snappy and after running for a short while it gets super laggy :/

I'm guessing it's because SDL3 can and will resize buffers as it wants to, whereas I'd rather it just go crazy if it under runs.

@aeva I was curious about this buffer-resize as I've done some audio code in the past, but not with SDL3(yet). that would be frustrating to write well-timed audio code if it dynamically resized things on the fly rather than doing audio dropouts on buffer exhaustion.

Iooks like there are hints you can set to force a buffer size in frames https://wiki.libsdl.org/SDL3/SDL_HINT_AUDIO_DEVICE_SAMPLE_FRAMES

Not sure if this could help? It doesn't seem to promise this will work, so may still need to fetch the actual buffer size gotten back.

SDL3/SDL_HINT_AUDIO_DEVICE_SAMPLE_FRAMES

The Simple Directmedia Layer Wiki

aeva May 2, 2025

@eggboycolor my program sets that hint. best I can tell it does nothing

egg boy color May 2, 2025

@aeva darn. hope you're able to figure out something there :< maybe audio backend specific, if you don't mind diving through sdl's code/statically linking stuff with symbols to do more debugging, but yeah these sorts of latency things are indeed messy if they (or the backend they wrap) don't give easy direct control over buffers.

either way curious to know what comes of it, since it's been really cool following your thread especially re:applying Vulkan for real-time audio!

aeva May 2, 2025

@eggboycolor I'll probably have to do something like that, though I might just rip out the SDL stuff and hammer ALSA directly