Mandelbrot Fractal GLSL

GLSL Mandelbrot

vec2 center = vec2(0.8,0);
float blue = 0.3; 

void main() {
    vec2 z, c;
    float scale = 20.0/iGlobalTime; // zoom in
    vec2 uv = gl_FragCoord.xy / iResolution.xy;

    c.x = 1.3333 * (uv.x - 0.5) * scale - center.x;
    c.y = (uv.y - 0.5) * scale - center.y;
    z = c;
    vec4 col = vec4(0,0,0,0);
	
    for(int i=0; i<100; i++) {
        float x = (z.x * z.x - z.y * z.y) + c.x;
        float y = (z.y * z.x + z.x * z.y) + c.y;		
	blue += 0.028; 
	if((x * x + y * y) > 4.0) {
            col = vec4(0,0,blue,0);
            break;
        }
        z.x = x;
        z.y = y;
    }
    gl_FragColor = col;
}