#version 430
layout(local_size_x = 1, local_size_y = 1) in;
layout(rgba32f, binding = 0) uniform image2D texture;

// perlin noise taken from https://gist.github.com/patriciogonzalezvivo/670c22f3966e662d2f83

#define M_PI 3.14159265358979323846

float rand(vec2 co){return fract(sin(dot(co.xy ,vec2(12.9898,78.233))) * 43758.5453);}
float rand (vec2 co, float l) {return rand(vec2(rand(co), l));}
float rand (vec2 co, float l, float t) {return rand(vec2(rand(co, l), t));}

float perlin(vec2 p, float dim, float time) {
	vec2 pos = floor(p * dim);
	vec2 posx = pos + vec2(1.0, 0.0);
	vec2 posy = pos + vec2(0.0, 1.0);
	vec2 posxy = pos + vec2(1.0);

	float c = rand(pos, dim, time);
	float cx = rand(posx, dim, time);
	float cy = rand(posy, dim, time);
	float cxy = rand(posxy, dim, time);

	vec2 d = fract(p * dim);
	d = -0.5 * cos(d * M_PI) + 0.5;

	float ccx = mix(c, cx, d.x);
	float cycxy = mix(cy, cxy, d.x);
	float center = mix(ccx, cycxy, d.y);

	return center * 2.0 - 1.0;
}

void main() {
	ivec2 pixelCoords = ivec2(gl_GlobalInvocationID.xy);
	vec2 coords = vec2(pixelCoords) / vec2(512);

	// TODO: proper wood texture generation
	imageStore(texture, pixelCoords, (0.5+perlin(coords / 25, 512.0, 0.0)) * vec4(110, 51, 7, 255) / 255);
}