windowFor

pub fn windowFor(self: *const Subwindows, p: Point.Physical) Id {
    var i = self.stack.items.len;
    while (i > 0) : (i -= 1) {
        const sw = &self.stack.items[i - 1];
        if (sw.mouse_events and (sw.modal or sw.rect_pixels.contains(p))) {
            return sw.id;
        }
    }
    return .zero;
}