var dx = keyboard_check(vk_right) - keyboard_check(vk_left);
var dy = keyboard_check(vk_down)  - keyboard_check(vk_up);

// normalise the diagonal
if (dx != 0 && dy != 0) {
    dx *= 0.7071;
    dy *= 0.7071;
}
hsp = dx * 3;
vsp = dy * 3;
// ... place_meeting blocks from Episode 2 ...

depth = -y;    // lower on screen = in front