* @param end
* @param duration
*/
public void slide(Point start, Point end, int duration) {
if (contents[start.x][start.y] != null) {
Animation anim = new SlideAnimation(contents[start.x][start.y], new Point(start.x * cellWidth, start.y * cellHeight), new Point(end.x * cellWidth, end.y * cellHeight), duration);
contents[start.x][start.y] = null;
imageChanged[start.x][start.y] = true;
redraw();
animations.add(anim);
if (animationManager == null) {