#version 450

layout(local_size_x = 64) in;

layout(rgba32f, binding = 0) uniform image2D particleStateImage;
layout(rgba32f, binding = 2) uniform image2D particleVelocityImage;

layout(std140, binding = 1) uniform Params {
	uint particleCountX;
	uint particleCountY;
	uint seed;
	uint _pad;
};

uint hash(uint x) {
	x ^= x >> 16u;
	x *= 0x45d9f3bu;
	x ^= x >> 16u;
	x *= 0x45d9f3bu;
	x ^= x >> 16u;
	return x;
}

float hashFloat(uint x) {
	return float(hash(x)) / float(0xFFFFFFFFu);
}

void main() {
	uint gid = gl_GlobalInvocationID.x;
	uint count = particleCountX * particleCountY;
	if (gid >= count) {
		return;
	}

	uint s = gid * 3u + seed;

	float direction = hashFloat(s) * (3.14159265 * 2.0);
	float speed = (0.1 + hashFloat(s + 1u) * 0.1) * 320.0;

	vec2 velocity = vec2(cos(direction) * speed, sin(direction) * speed);
	float lifetime = 1.5 + hashFloat(s + 2u) * 1.5;

	ivec2 coord = ivec2(
		int(gid % particleCountX),
		int(gid / particleCountX));
	imageStore(particleStateImage, coord, vec4(0.0, 0.0, lifetime, 0.0));
	imageStore(particleVelocityImage, coord, vec4(velocity, 0.0, 0.0));
}