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#version 330

out vec4 fragColor;

uniform vec2 res;
uniform float time;

const float sharpness = 300;

const float PI = 3.14159265358979323846;


mat2 rot(float a) {
        return mat2(
                cos(a), -sin(a),
                sin(a), cos(a)
        );
}

float poly(float n, vec2 m, float r, float rt, vec2 p) {
        vec2 diff = (m - p) * rot(rt);
        float d = length(diff);
        float alpha = PI / n;
        float gamma = mod(abs(atan(diff.x, diff.y)), alpha*2);

        if (gamma > alpha)
                gamma -= 2*alpha;

        float r2 = r * cos(alpha) / cos(gamma);

        return clamp((r2 - d)*sharpness, 0.0, 1.0);
}

float poly_d(float n, vec2 m, float r, float rt, vec2 p) {
        return poly(n, m, r, rt, p) - poly(n, m, r - 1/sharpness, rt, p);
}

void main(void) {
        vec2 m = res/2;
        float s = min(m.x, m.y);
        vec2 p = (gl_FragCoord.xy - m) / s;

        float scene = 0;

        float c;

        c = poly_d(5 - 3*cos(time/1000), vec2(0, 0), 0.5, PI * time/1000, p);
        scene = abs(scene - c);

        c = poly_d(5 - 3*cos(time/1000), vec2(0, 0), 0.5, -PI * time/1000, p);
        scene = abs(scene - c);

        fragColor = vec4(vec3(1, 1, 1) * scene, 1);
}