Glowing Square

#ifdef GL_ES
precision mediump float;
#define GLSLIFY 1
#endif

uniform vec2 u_resolution;
uniform float u_time;
uniform vec2 u_mouse;

#define GLSLIFY 1
float random (vec2 st) {
    return fract(sin(dot(st.xy, vec2(12.9898,78.233)))*43758.5453123);
}

#define M_SQRT_2 1.41421356
float square(vec2 P, float size){
    return abs(max(abs(P.x), abs(P.y)) - size/(2.0*M_SQRT_2));
}

float glow(float d, float str, float thickness){
    return thickness / pow(d, str);
}

void main() {
    vec2 uv = gl_FragCoord.xy/u_resolution.xy;
    // uv.x *= u_resolution.x/u_resolution.y;
    vec2 uvs = fract(uv * 6.);
    vec2 ipos = floor(uvs);
    vec2 fpos = fract(uvs);
    uv = fpos * 2.0 - 1.0;

    float circle_dist = square(uv, 0.75 + 0.45*random(ipos));

    float glow_circle = glow(circle_dist, 0.328, 0.56);
    vec3 color = vec3(glow_circle);
        
    gl_FragColor = vec4(color * vec3(.3,.4,.65), 1.0);
}