implementing random function for strands

[perminder-17]

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[perminder-17]

Hi @davepagurek and @ksen0 , sorry for the delay, its open for the review, Can you please check once?

[davepagurek]

Thanks for taking this on, the structure is looking good! I left one thing about possibly making the call index a runtime thing instead of compile time to better support for loops, and maybe we could add a test case for vertex + fragment shaders too?

[davepagurek]

I think that means that if you were to call random() in a for loop, e.g.:

let data = uniformStorage(someStorage)

for (let i = 0; i < 5; i++) {
  data[i] += random()
}

...then they'd all get the same random value added to them because random here is just one AST node and would have one fixed call index, translating into something like:

for (var i = 0; i < 5; i++) {
  data[i] += random(seed, 0);
}

Do we have the option of making the call index be a global variable in the shader code so that it's not fixed? e.g something like:

var<private> invocation: i32 = 0;
fn random(seed: f32) -> f32 {
  let val = ...; // Do random gen here, using `invocation`
  invocation++;
  return val;
}

// So then the call site is just:
for (var i = 0; i < 5; i++) {
  data[i] += random(seed);
}

[davepagurek]

nice work generalizing this!