A trajectory can be difficult to interpret when played only from its starting frame to its ending frame. You may want to revisit a transition, compare conformations in the opposite order, or simply inspect how a structure arrived at a particular state. In SAMSON, Play reverse path lets you do that without changing the path itself: it plays the selected path backward between two animation keyframes.
Reverse playback is especially useful as a viewing tool. It can help you retrace a conformational change or review a trajectory from its endpoint toward its beginning. Keep in mind that playing a path backward changes the order in which its frames are displayed; it does not, by itself, establish that the molecular process is physically reversible.
Set up a reverse playback
First, select the path or paths you want to review. In SAMSON, a path node is used to store a trajectory. With your selection made, open the Animation panel in the Animator and double-click Play reverse path.
The animation plays the whole path in reverse between its two keyframes. Those keyframes define the interval over which the animation runs, and you can move them as needed. This is useful when you want the reverse playback to occupy a particular part of a larger presentation or animation sequence.
When you select more than one path
If you select multiple paths before adding the animation, SAMSON synchronizes them. This can make a side-by-side review easier when several paths need to be played in reverse together. Before starting, check that you selected the paths you intend to compare; synchronized playback applies to the selected paths.
Check the frame counts
The number of frames in the animation may differ from the number of frames in the path. When they do, the path is smoothed. If you need to change that behavior, you can switch smoothing off in the Inspector.
This setting is worth checking when the playback does not appear to map one animation frame to one path frame. Smoothing affects how the path is represented across the animation frames; it does not change the fact that the selected path is being played in reverse.
Adjust the feel of transitions
You can also change how parameters are interpolated between frames by modifying the Easing curve. If the movement feels too abrupt or uneven for the presentation you are building, inspect the easing options and adjust them to suit the way you want the transition displayed.
A practical review sequence is simple: select the trajectory, add Play reverse path, position the animation keyframes, then check smoothing and easing if the playback needs adjustment. These controls help you distinguish between the path’s frame order, the animation’s duration, and the way motion is interpolated for display.
For details and the illustrated options, see the Play reverse path documentation.
Note: SAMSON and all SAMSON Extensions are free for non-commercial use. Get SAMSON.