#define DO_RED


float sdCircle(vec2 p, float r) {
    return length(p) - r;
}

float sdBox(vec2 p, vec2 b) {
    vec2 d = abs(p) - b;
    return length(max(d, 0.0)) + min(max(d.x, d.y), 0.0);
}

void main() {
    vec2 uv = (fragTexCoord * 2.0 - 1.0) * vec2(iResolution.x / iResolution.y, 1.0);
    vec2 m = (iMouse / iResolution - 0.5) * 2.0 * vec2(iResolution.x / iResolution.y, 1.0);
    m.y = -m.y;  // Raylib
    float t = iTime * 0.8;

    /* rotating box */
    float angle = t;
    vec2 rot = vec2(cos(angle) * uv.x - sin(angle) * uv.y,
                    sin(angle) * uv.x + cos(angle) * uv.y);
    float box = sdBox(rot, vec2(0.3));

    /* pulsing circle that follows mouse */
    float pulse = 0.05 + 0.02 * sin(iTime * 3.0);
    float circle = sdCircle(uv - m, pulse);

    /* combine */
    float d = min(box, circle);

    /* coloring */
#ifdef DO_RED
    vec3 col = mix(vec3(0.05), vec3(1.0, 0.2, 0.1), 1.0 - smoothstep(0.0, 0.01, d));
    col += vec3(0.1, 0.4, 1.0) * (1.0 - smoothstep(0.0, 0.01, abs(d) - 0.005));
    col += min(0.03 / abs(d), 1.0) * vec3(1.0, 0.3, 0.2);
#else
    vec3 col = mix(vec3(0.05), vec3(0.2, 0.6, 1.0), 1.0 - smoothstep(0.0, 0.01, d));
    col += vec3(1.0, 0.4, 0.1) * (1.0 - smoothstep(0.0, 0.01, abs(d) - 0.005));
    col += min(0.03 / abs(d), 1.0) * vec3(0.3, 0.6, 1.0);
#endif

    finalColor = vec4(col, 1.0);
}