#ifdef GL_ES
precision highp float;
#endif

uniform vec2 u_resolution;
uniform float u_time;
uniform float u_speed;

void main(void)
{
    vec2 p = -1.0 + 2.0 * gl_FragCoord.xy / u_resolution.xy;
    vec2 cc = vec2( cos(.25*u_time*u_speed), sin(.25*u_time*u_speed*1.423) );

    float dmin = 1000.0;
    vec2 z  = p*vec2(1.33,1.0);
    for( int i=0; i<64; i++ )
    {
        z = cc + vec2( z.x*z.x - z.y*z.y, 2.0*z.x*z.y );
        float m2 = dot(z,z);
        if( m2>100.0 ) break;
        dmin=min(dmin,m2);
        }

    float color = sqrt(sqrt(dmin))*0.7;
    gl_FragColor = vec4(color,color,color,1.0);
}