// GPU procedural Perlin noise texture generator.
// Fractional Brownian Motion using value noise.

#include "math/noise"

struct PerlinParams {
  width: u32,
  height: u32,
  seed: f32,
  frequency: f32,
  amplitude: f32,
  amplitude_decay: f32,
  octaves: u32,
  _pad0: f32,  // Padding for alignment
}

@group(0) @binding(0) var output_tex: texture_storage_2d<rgba8unorm, write>;
@group(0) @binding(1) var<uniform> params: PerlinParams;

@compute @workgroup_size(8, 8, 1)
fn main(@builtin(global_invocation_id) id: vec3<u32>) {
  if (id.x >= params.width || id.y >= params.height) { return; }

  let uv = vec2<f32>(f32(id.x) / f32(params.width),
                      f32(id.y) / f32(params.height));

  var value = 0.0;
  var amplitude = params.amplitude;
  var frequency = params.frequency;
  var total_amp = 0.0;

  for (var o: u32 = 0u; o < params.octaves; o++) {
    let p = uv * frequency + params.seed;
    value += noise_2d(p) * amplitude;
    total_amp += amplitude;
    frequency *= 2.0;
    amplitude *= params.amplitude_decay;
  }

  value /= total_amp;
  let clamped = clamp(value, 0.0, 1.0);

  textureStore(output_tex, id.xy, vec4<f32>(clamped, clamped, clamped, 1.0));
}