//Cut out surface
if(!surface_exists(cutout)){
    cutout = surface_create(room_width,room_height);
    surface_set_target(cutout);

    draw_clear_alpha(c_black,1);

    draw_set_blend_mode(bm_subtract);
    draw_sprite(sLayer,0,x,y);
    draw_set_blend_mode(bm_normal);

    surface_reset_target();
}

if(!surface_exists(cake)){
    cake = surface_create(room_width,room_height);
    surface_set_target(cake);

    draw_set_blend_mode(bm_subtract);
    draw_surface(cutout,0,0);
    draw_set_blend_mode(bm_normal);

    surface_reset_target();
}else{
    //Paint
    if(mouse_check_button(mb_left)){
        surface_set_target(cake);

        draw_set_color(oBrush.color);
        draw_circle(mouse_x,mouse_y,8,false);
        draw_line_width(mouse_xprev, mouse_yprev, mouse_x, mouse_y, 16);

        surface_reset_target();
    }

    draw_surface(cake,0,0);
    mouse_xprev = mouse_x;
    mouse_yprev = mouse_y;
}