#version 330 core
out vec4 FragColor;
uniform vec2 WindowSize;
uniform float time;

float rand(ivec2 co) {
    return fract(sin(dot(co, vec2(12.9898, 78.233))) * 43758.5453);
}

float cell_size = 0.1;

#define PI 3.1415926538

// whatever that corner contributes
float c_dot(vec2 point, vec2 corner) {
    ivec2 c = ivec2(round(corner * 10000));
    float angle = rand(c) * 2*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;
}

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

// better than built in smoothstep.
float fade(float t) {
	return ((6*t - 15)*t + 10)*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 u = smoothstep(0, 1, tile_uv.x);
    //float v = smoothstep(0, 1, tile_uv.y);
    //float val = smoothstep(tile_uv.x, smoothstep(tile_uv.y, c_bl_dot, c_tl_dot), smoothstep(tile_uv.y, c_br_dot, c_tr_dot));
    float val = lerp(lerp(c_tl_dot, c_bl_dot, v), lerp(c_tr_dot, c_br_dot, v), u);
    //float val = tile_uv.y;
    //float val = c_bl_dot*2 + 0.5;
    //val = val * 20;
    float out_val = val /2 + 0.5;
    FragColor = vec4(out_val, out_val, out_val, 1);

    //float yes = 0.5 + (c_dot(uv, c_tl) + c_dot(uv, c_tr) + c_dot(uv, c_bl) + c_dot(uv, c_br)) / 2;
    //FragColor = vec4(yes, yes, yes, 1);
}