Diary During Summer Vacation 17

3 hours of work tonight, a snapshot functionality has been added. Besides the ability for unlimited undo and redo, the rendering engine is now able to take snapshots and record those significant steps showing clearly how a knot can be tied. These snapshots are acturally recorded as a list of point list. Each time, a snapshot is taken, the rendering engine copies the current string state which is a set of points, and add it onto the snapshot list. Later when the user wants see or show others how a knot is tied, the animation playing function plays (renders) the snapshots one by one back into the scene.