A trajectory can be difficult to understand when you only watch it move in one direction. You may want to revisit how a structure arrived at a particular conformation, compare the order of visible changes, or simply replay a transition while focusing on a different part of the model. In SAMSON, the Play reverse path animation lets you play a path backward between two animation frames.
This is useful when reviewing a stored trajectory: instead of manually stepping through frames or rebuilding the sequence, you can add a reverse-play animation and watch the path run in the opposite direction. The animation is a viewing and presentation tool; reversing the playback does not, by itself, establish that the molecular process is physically reversible.
Set up a reverse playback
- Choose the path. Select the Path node containing the trajectory you want to review. In SAMSON, a path node is used to store a trajectory.
- Add the animation. In the Animator, open the Animation panel and double-click Play reverse path.
- Check the keyframes. The whole selected path is played in reverse between the animation’s two keyframes. Move those keyframes if you need to adjust where the animation begins or ends.
This workflow can make a review session more deliberate. For example, after noticing a change near the end of a trajectory, replaying the path backward can help you inspect the preceding conformations in sequence. You can pause your broader analysis at a point of interest and revisit the path without changing the order in which the trajectory was stored.
Playing several paths together
If you select more than one path before adding the animation, the paths are synchronized. This can be useful when you want to review multiple paths together rather than starting each playback separately. Before interpreting what you see, make sure you have selected the paths you intend to compare and check that their playback is easy to follow in the scene.
What to check if playback looks different than expected
The number of frames in the animation may not match the number of frames in the path. When they differ, the path is smoothed. If you want to change that behavior, you can switch smoothing off in the Inspector. This setting matters when you are examining a trajectory frame by frame: smoothing affects how the animation is presented between frames, so consider whether it suits the kind of review you are doing.
You can also change how parameters are interpolated between frames by modifying the animation’s Easing curve. If the movement seems too abrupt or too gradual for a presentation, inspect the easing options rather than assuming the underlying path has changed. The path itself and the way the animation moves between its frames are separate things to keep in mind.
A quick review checklist
- Confirm that the intended Path node or paths are selected.
- Set the animation keyframes to cover the portion you want to review.
- If the number of animation frames differs from the path, decide whether smoothing is appropriate.
- Adjust the easing curve if you need a different interpolation feel between frames.
- When comparing several paths, remember they will be synchronized.
Reverse playback is a small but practical addition to trajectory review: it gives you another direction from which to inspect a sequence, while keeping the original path available. For the full instructions, see the Play reverse path documentation.
Note: SAMSON and all SAMSON Extensions are free for non-commercial use. Get SAMSON.