#version 320 es

precision highp float;
precision highp int;
precision lowp sampler2D;
precision lowp samplerCube;

uniform vec2 WindowSize;
uniform float time;
layout(location = 0) out vec4 color;

float lerp(float a, float b, float x) {
    return a + x*(b-a);
}

uint xxhash32(uvec2 p) {
    const uint PRIME32_2 = 2246822519U, PRIME32_3 = 3266489917U;
	const uint PRIME32_4 = 668265263U, PRIME32_5 = 374761393U;
    uint h32 = p.y + PRIME32_5 + p.x*PRIME32_3;
    h32 = PRIME32_4*((h32 << 17) | (h32 >> (32 - 17)));
    h32 = PRIME32_2*(h32^(h32 >> 15));
    h32 = PRIME32_3*(h32^(h32 >> 13));
    return h32^(h32 >> 16);
}

//const uint k = 1103515245U;
//
//vec3 hash33( uvec3 x ) {
//    x = ((x >> 8U) ^ x.yzx) * k;
//    x = ((x >> 8U) ^ x.yzx) * k;
//    x = ((x >> 8U) ^ x.yzx) * k;
//    return vec3(x) * (1.0 / float(0xffffffffU));
//}

float rand(vec2 v, float seed) {
    uint hash = xxhash32(uvec2(v * 10000.0 + seed * 10000.0));
    return float(hash) * (1.0/float(0xffffffffu));
}

float cell_size = 0.01;
#define PI 3.1415926538

// whatever that corner contributes
float c_dot(vec2 point, vec2 corner) {
    vec2 c = vec2(ivec2(round(corner * 100.0)));
    float angle = rand(c, 0.0) * 2.0*PI;
    vec2 random_corner_vec = vec2(cos(angle), sin(angle));
    vec2 offset = (point - corner) / cell_size;
    float dot_product = dot(random_corner_vec, offset);
    // for now just return something
    return dot_product;
}

// better than built in smoothstep.
float fade(float t) {
	return ((6.0*t - 15.0)*t + 10.0)*t*t*t;
}


void main() {
    // We'll make origin in the top-left.
    vec2 uv = gl_FragCoord.xy / WindowSize;
    uv.y = 1.0 - uv.y;
    vec2 grid_edge_offset = mod(uv, cell_size);
    // c: corner
    vec2 c_tl = uv - grid_edge_offset;
    vec2 c_tr = uv - grid_edge_offset + vec2(cell_size, 0);
    vec2 c_bl = uv - grid_edge_offset + vec2(0,         cell_size);
    vec2 c_br = uv - grid_edge_offset + vec2(cell_size, cell_size);
    float c_tl_dot = c_dot(uv, c_tl);
    float c_tr_dot = c_dot(uv, c_tr);
    float c_bl_dot = c_dot(uv, c_bl);
    float c_br_dot = c_dot(uv, c_br);

    // the uv within the tile (0 to 1)
    vec2 tile_uv = (uv - c_tl) / cell_size;

    // lerp index
    float u = fade(tile_uv.x);
    float v = fade(tile_uv.y);
    //float u = tile_uv.x;
    //float v = tile_uv.y;
    float val = lerp(lerp(c_tl_dot, c_bl_dot, v), lerp(c_tr_dot, c_br_dot, v), u);
    float out_val = val /2.0 + 0.5;
    //uvec3 p = uvec3(uint(round(uv.x * 500.0)), uint(round(uv.y * 500.0)), 1);
    //color = vec4( hash33(p), 1.0 );
    //float lel = noise(vec3(uv * 10.0, 1.0));
    //float lel = gold_noise(uv, time * 100.0);
    //float lel = random( uv.x * 100.0 );
    float lel = rand(uv, 0.0);
    color = vec4(lel, lel, lel, 1.0);
}