Writing Kernels

A Kernel contains the WGSL code that runs on the GPU.

import { Kernel } from '@volten/core';

const scale = new Kernel(`
  fn main(gid: vec3u) {
    output[gid.x] = input[gid.x] * multiplier;
  }
`);

You write a main function. Volten adds the compute entry point, workgroup size, bindings, and safety guard around it.

Builtin Shorthands

Volten expands a few parameter names in main:

Name	Type	Meaning
`gid`	`vec3u` or `vec3<u32>`	Global invocation id
`lid`	`u32`	Local invocation index
`lid3`	`vec3u` or `vec3<u32>`	Local invocation id
`wid`	`vec3u` or `vec3<u32>`	Workgroup id
`nwg`	`vec3u` or `vec3<u32>`	Number of workgroups

const kernel = new Kernel(`
  fn main(gid: vec3u, lid: u32) {
    data[gid.x] = f32(lid);
  }
`);

You can also write the full WGSL builtin syntax yourself.

fn main(@builtin(global_invocation_id) gid: vec3u) {
  data[gid.x] = data[gid.x] * 2.0;
}

Helper Functions

Only the function named main is treated as the kernel entry point. Other functions are left alone.

const kernel = new Kernel(`
  fn square(x: f32) -> f32 {
    return x * x;
  }

  fn main(gid: vec3u) {
    data[gid.x] = square(data[gid.x]);
  }
`);

Labels

Add a label when you want clearer debug output and browser GPU tooling names.

const kernel = new Kernel(`...`, {
    label: 'scale values'
});