conditional compilation today for lygia webgpu

[mighdoll]

There are a few lygia WebGPU files calling for conditional compilation in lygia. e.g. rbg2xyz. They're in comments now of course, since wgsl doesn't support conditional compilation. I'll bet there are more conditions in the glsl that haven't been ported to WebGPU yet too.

Here's the rgb2xyz example:

// #ifdef CIE_D50
// const mat3 RGB2XYZ = mat3(
//     0.4360747, 0.2225045, 0.0139322,
//     0.3850649, 0.7168786, 0.0971045,
//     0.1430804, 0.0606169, 0.7141733);
// #else
const RGB2XYZ = mat3x3<f32>(
    0.4124564, 0.2126729, 0.0193339,
    0.3575761, 0.7151522, 0.1191920,
    0.1804375, 0.0721750, 0.9503041 );
// #endif
// #endif

fn rgb2xyz(rgb: vec3f) -> vec3f { return RGB2XYZ * rgb; }

With WESL, we can support that now like this:

@if(CIE_D50)
const mat3 RGB2XYZ = mat3(
     0.4360747, 0.2225045, 0.0139322,
     0.3850649, 0.7168786, 0.0971045,
     0.1430804, 0.0606169, 0.7141733);

@if(!CIE_D50)
const RGB2XYZ = mat3x3<f32>(
    0.4124564, 0.2126729, 0.0193339,
    0.3575761, 0.7151522, 0.1191920,
    0.1804375, 0.0721750, 0.9503041 );

fn rgb2xyz(rgb: vec3f) -> vec3f { return RGB2XYZ * rgb; }

I can send a PR to do that for some of the existing cases. That'll work for typical users.

Later, there's more to do on the WESL side to make it nicer, but I don't think we need wait. e.g. in the future we should probably support @else as well as @if. And we should define a way to set condition values from shaders not just JavaScript..

[patriciogonzalezvivo]

@mighdoll this issue really speaks to my heart. LYGIA relays a lot on conditional compilation not just for diverging standards, but also for flexibility and pseudo templating.

Check some of this examples:

• https://github.com/patriciogonzalezvivo/lygia_examples/blob/main/lighting_atmosphere.frag#L36
• https://github.com/patriciogonzalezvivo/lygia_examples/blob/main/lighting_raymarching_pbr.frag#L30
• https://github.com/patriciogonzalezvivo/lygia_examples/blob/main/lighting_raymarching_pbrGlass.frag#L32
• https://github.com/patriciogonzalezvivo/lygia_examples/blob/main/sample_bracketing.frag#L19
• https://github.com/patriciogonzalezvivo/lygia_examples/blob/main/sample_dither.frag#L14
• https://github.com/patriciogonzalezvivo/lygia_examples/blob/main/filter_gaussianBlur2D.frag#L14

As you see I have grow to relay on it a lot. And is one of the things I really miss in WGSL to the point that in my opinion makes it a harsh and unexpressive language. If WEGS can address some of this issues would make WebGPU SO much expressive, flexible and interesting for create/prototyping. IMO

Thank you again for fighting the good fight out there!

Let me know how I can help

[mighdoll]

Oh, thanks for pulling out those clear examples! We want to steer WESL to solve real WebGPU user problems first, and putting a spotlight on concrete issues is so valuable.

More generally, I think it's time now for WebGPU community tools and libraries. If Lygia can make a valuable library, and WESL can make it easy to use, that'll go a long way. Shader coding is hard enough. Together I think we can make it easier for everyone. Once we get the basics working, maybe we can make some examples together to help spread the word too.

For the conditions part (#ifdef), I think it's probably worth trying to use the existing WESL @if stuff. I'll try porting over some easy cases and send a PR to get started - we can see what works/doesn't work from there. I see from your examples above that we'll want to add some way to set conditions from the shaders (#define ARROWS_STYLE_LINE), not just from JavaScript. We can add that part later.

Macros/templating like #define GAUSSIANBLUR_SAMPLER_FNC(TEX, UV) sampleClamp2edge(TEX, UV) are interesting.. I imagine WESL/WGSL will eventually want some kind of integrated language feature like interfaces or generics. That'd be type checked by tools, and supportable by the forthcoming language server.

But I think we should look at putting in some kind of less safe but more flexible approach sooner. Perhaps some preprocessor combined with interface declarations would get us flexibility but still keep the language tools happy...

WESL implementations have a flexible hook for injecting arbitrary shader code from JavaScript/Rust - (virtual modules). That's an example of adding flexibility even at the cost of language purity.

[mighdoll]

For the conditions part (#ifdef), I think it's probably worth trying to use the existing WESL @if stuff. I'll try porting over some easy cases and send a PR to get started

I added a PR here: mighdoll#2 that you can review, converting a few #ifdef cases to WESL's @if syntax.

Github won't let us stack PRs, so the PR's against my lygia fork. That's just for readability, to isolate the changes from the other pending bits.