#version 100
precision highp float;

uniform float u_time;
uniform vec2 u_resolution;
uniform float u_zoom;
uniform vec2 u_center;

void main() {
    // Current pixel coordinate in 0..1
    vec2 st = gl_FragCoord.xy / u_resolution.xy;
    st.x *= u_resolution.x / u_resolution.y; // Aspect ratio correction
    
    // Map to Mandelbrot space using Zoom and Center
    // Default (Zoom 1): -2.5 to 1.5 X, -1.5 to 1.5 Y approx?
    // Let's say center is 0,0. Range -2..2.
    // st is 0..AspectRatio (approx 0..1.7)
    
    // Center the coords:
    vec2 c_uv = (gl_FragCoord.xy - u_resolution.xy * 0.5) / u_resolution.y;
    
    // Apply Zoom and Pan
    vec2 c = (c_uv / u_zoom) + u_center;

    // Mandelbrot iteration
    vec2 z = vec2(0.0);
    float iter = 0.0;
    float max_iter = 100.0 + log(u_zoom) * 20.0; // Increase details with zoom
    
    for (float i = 0.0; i < 500.0; i++) {
        if (i > max_iter) break;
        // Z = Z^2 + C
        float x = (z.x * z.x - z.y * z.y) + c.x;
        float y = (z.y * z.x + z.x * z.y) + c.y;
        
        if ((x * x + y * y) > 4.0) {
            iter = i;
            break;
        }
        z.x = x;
        z.y = y;
    }
    
    // Coloring
    float t = iter / max_iter;
    if (iter == 0.0) {
        gl_FragColor = vec4(0.0, 0.0, 0.0, 1.0);
    } else {
        gl_FragColor = vec4(
            sqrt(t),
            t * t,
            sin(t * 3.1415),
            1.0
        );
    }
}