A molecular trajectory can be difficult to interpret when you only watch it move in one direction. A conformational change may happen quickly, a structural feature may be easier to notice on the way back, or you may simply want to retrace the frames while presenting a model. In SAMSON, Play reverse path lets you review a stored path in reverse, without rebuilding the trajectory.
This is a visualization tool, not a way to calculate a new reverse process. It plays the selected path backward between two animation keyframes. That distinction matters: a reversed playback can help you inspect and communicate a trajectory, but by itself it does not establish that the molecule would follow the same route in a physical experiment or simulation run in reverse.
Set up a reverse playback
First, select the Path node containing the trajectory you want to review. Then open the Animation panel in the Animator and double-click Play reverse path. The animation plays the path in reverse between its two keyframes. You can move those keyframes to adjust where the animation begins and ends in the larger presentation.
This sequence can be useful when you are preparing a focused review rather than replaying an entire presentation. For example, position the animation keyframes around the part of the timeline you want viewers to examine, then use the reverse playback to revisit that segment. The animation works with one path or multiple paths. If you select multiple paths, they are synchronized, which can make it easier to review related paths together.
Check the frame counts and smoothing
A common source of unexpected-looking playback is a mismatch between the number of frames in the animation and the number of frames in the path. When the counts are not equal, SAMSON smooths the path. Smoothing can make movement appear more continuous, but it also affects how the stored frames are displayed across the animation.
If you need to inspect the path without that smoothing, you can switch it off in the Inspector. This gives you a useful check when the playback seems different from the frame-by-frame trajectory you expected. Before drawing conclusions from the visual result, it is worth checking whether smoothing is enabled and whether the animation and path have matching frame counts.
Adjust the feel without changing the path
The Easing curve controls how parameters are interpolated between frames. Adjusting it changes the timing profile of the animation, which can help make a presentation easier to follow. It does not replace the underlying path: think of easing as controlling the transition between frames in the animation, rather than editing the molecular trajectory itself.
A practical review checklist
- Confirm the selected Path. The animation plays the path or paths you selected.
- Set the keyframes. Move them to define the portion of the presentation in which the reverse playback occurs.
- Check synchronization. If using multiple paths, remember that they play in synchronization.
- Inspect smoothing. If path and animation frame counts differ, check the smoothing setting in the Inspector.
- Choose an easing curve deliberately. Use it to adjust interpolation for clearer viewing, not as evidence of a different trajectory.
Reverse playback is a small but useful option when reviewing a trajectory: it lets you revisit the same stored path from the opposite direction, adjust its timing in an animation, and check how smoothing affects what you see. For setup details, see the Play reverse path documentation.
Note: SAMSON and all SAMSON Extensions are free for non-commercial use. Get SAMSON.