adding debug_printf like in vulkan

[Arne-Berner]

Hejhej! I saw a discussion about vulkan having debug_printf on discord, linking to these docs:
https://github.com/KhronosGroup/Vulkan-ValidationLayers/blob/main/docs/debug_printf.md

This has been proposed in wgsl before:
gpuweb/gpuweb#4348

But it has been dropped since.
This issue also seems to talk about it: gpuweb/gpuweb#4704
There is also a proposal for a print buffer.

What do you think, is this worth investigating? A discussion on discord noted that you can create this behaviour yourself by using a storage buffer + an atomic counter.

[stefnotch]

I think this is absolutely worth having. Especially the fact that WGSL does not have a syntax for strings/format strings has no easy workaround.

[stefnotch]

@TimTheBig

Strings are not currently on the radar of the working group. They're in milestone 3/4.
However, the group is interested in doing something there in the future.

Since I assume that you prefer having a solution today, here are the most promising avenues

• wgpu had a pull request for such an extension. So far, it seems like it mostly needs someone to put in the work of properly recreating this Debug printf in shaders gfx-rs/wgpu#4297
• WESL wants to have strings. But we'd first have to figure out the semantics. Well researched proposals are very appreciated. When I write such a proposal, I usually follow the Rust RFC template

[TimTheBig]

While adding strings as a WESL feature is tempting I feel that getting it into WGSL is a much better option, though I don't know how long such a proposal will take

[TimTheBig]

I'm trying to push gpuweb/gpuweb#4704 to a PR

[TimTheBig]

• wgpu had a pull request for such an extension. So far, it seems like it mostly needs someone to put in the work of properly recreating this Debug printf in shaders gfx-rs/wgpu#4297

If I where to do so would @stefnotch be willing to review before I open the PR, as that would help the initial PR review go faster?

[stefnotch]

@TimTheBig Absolutely! I'd also be happy to assist you whenever you have questions :)

On that note, the wgpu folks are absolutely lovely to talk to. They have office hours and a matrix server.

https://github.com/gpuweb/gpuweb/wiki/Meetings
https://matrix.to/#/%23wgpu:matrix.org

[TimTheBig]

Once I remake the PR the next step is strings in WGSL, correct?

Metal support using metal/logging-shader-debug-messages is also a goal of mine.

[stefnotch]

@TimTheBig Possibly yes! We should put it back onto their agenda, since debug logging would be useful to have everywhere.

On that note, do you have use cases for strings that go beyond debug logging?

[TimTheBig]

@stefnotch my branch is almost working.
All I have left to fix is two spr-v test failing with: UnsupportedCapability(Linkage)

I will fix the git history soon

[TimTheBig]

All I have left to fix is two spr-v test failing with: UnsupportedCapability(Linkage)

Fixed, all I had to do was add Linkage to SUPPORTED_CAPABILITIES in the spr-v mod

Now it's outputting nothing for tests with debug-printf

[stefnotch]

That sounds very promising! I'll take a closer look once the git history is in order, currently the diff view is struggling in an interesting way.

[k2d222]

TimTheBig/wgpu@71cc492...TimTheBig:wgpu:trunk

[TimTheBig]

Fixed git history in TimTheBig/wgpu@debug-print