__kernel void mandelbrot(__global unsigned char *out_buff, unsigned int iter, double cx, double cy, double xs, double ys, unsigned int width, unsigned int height)
{
	const int idx = get_global_id(0);

	unsigned int i;
	double z_real, z_imag;
	double z2_real, z2_imag;
	double pt_real, pt_imag;
	double color_scale;
	unsigned int r, g, b;

	const unsigned int pix_x = idx % width;
	const unsigned int pix_y = (unsigned int)idx / width;
	const double val_per_x_pixel = xs / (width - 1);
	const double val_per_y_pixel = ys / (height - 1); 
	

	pt_real = (((double)pix_x - (double)(width - 1) / 2)) * val_per_x_pixel + cx;
	pt_imag = (((double)pix_y - (double)(height - 1) / 2)) * val_per_y_pixel + cy;

	z_real = 0.0;
        z_imag = 0.0;	

	for (i = 0; i < iter; i++) {
		z2_real = z_real * z_real - z_imag * z_imag;
		z2_imag = 2.0 * z_real * z_imag;

		z_real = z2_real + pt_real;
		z_imag = z2_imag + pt_imag;

		if ((z_real * z_real + z_imag * z_imag) >= 4.0)
			break;
	}

    color_scale = (double)(i) / (double)iter;
    if (i != iter) {
	r = (unsigned char)(255.0 * sqrt((1-color_scale)));
	g = (unsigned char)(255.0 * color_scale*color_scale);
	b = (unsigned char)(255.0 * color_scale);
    } else {
	r = g = b = 0;
    }
    out_buff[idx*3] = r;
    out_buff[idx*3+1] = g;
    out_buff[idx*3+2] = b;
}