#version 100
precision mediump float;
uniform float u_time;
uniform vec2 u_resolution;

void main() {
    vec2 p = (2.0 * gl_FragCoord.xy - u_resolution.xy) / u_resolution.y;
    float a = atan(p.y, p.x);
    float r = length(p);
    vec2 uv = vec2(0.5 / r + 0.5 * u_time, a / 3.14159);
    
    // Simple checkerboard pattern
    float f = sin(uv.x * 20.0) * sin(uv.y * 20.0);
    vec3 col = vec3(f);
    
    // Fade to black in center
    col *= r;
    
    // Add some color
    col *= vec3(0.5 + 0.5 * sin(u_time), 0.5, 0.5 + 0.5 * cos(u_time));
    
    gl_FragColor = vec4(col, 1.0);
}