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

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

float cell_size = 0.1;

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);
    // random vectors
    vec2 c_tl_ran = rand(c_tl);
    vec2 c_tr_ran = rand(c_tr);
    vec2 c_bl_ran = rand(c_bl);
    vec2 c_br_ran = rand(c_br);
    // offset vectors
    vec2 c_tl_off = c_tl - uv;
    vec2 c_tr_off = c_tr - uv;
    vec2 c_bl_off = c_bl - uv;
    vec2 c_br_off = c_br - uv;

    FragColor = 
}