Molecular modelers often need to analyze conformational transitions, loop back through molecular motions, or visualize symmetry in paths taken by atoms or groups in simulations. While viewing trajectories forward is standard, playing them in reverse can be surprisingly valuable: it can aid in identifying reversible steps in molecular mechanisms, uncovering symmetry, or simply producing cyclic animations for presentations.
In SAMSON, this can be done easily using the Play reverse path animation. Let’s explore how this works, why you might need it, and how to make the most of it.
What Does “Playing a Path in Reverse” Mean?
When a path is created in SAMSON — for example, from morphing between two conformations or loading a trajectory — it’s stored as a Path node. The Play reverse path animation enables users to animate that path backwards between two keyframes on the timeline.
Instead of watching atoms move from conformation A to B, you watch B to A. It’s a subtle change that can make a big difference during analysis or when creating presentation materials.
Why Play a Path in Reverse?
- Symmetry analysis: Reverse animations help in identifying whether a molecular change is reversible or symmetric.
- Detection of artifacts: When you play motion in both directions, any artifacts or inconsistencies in the simulation or path interpolation become more apparent.
- Cyclic animations: For visualizing molecular motion in loops (e.g., opening and closing of a protein channel), combining forward and reverse animations creates a seamless oscillation.
- Presentation clarity: Sometimes the motion in one direction creates visual occlusion or distraction; playing it in reverse might improve visibility or emphasis.
How to Add a Reverse Path Animation
- First, select the Path node you want to animate. This could be a loaded trajectory or a morph.
- Then, open the Animator panel and locate the Animation panel.
- Double-click the Play reverse path animation effect. This adds the animation between two keyframes.
- Move or adjust the duration between the keyframes to control playback duration.
Customize the Playback
By default, if the number of animation frames and the number of path frames don’t match, SAMSON performs smoothing to interpolate the motion. You can disable this in the Inspector if you want raw, step-by-step transitions to be preserved.
Additionally, easing curves can be applied to adjust how the animation progresses. For example, you can slow down the beginning or the end of the animation. This can make your reverse playback more visually appealing — or more scientifically representative if you want to mimic acceleration/deceleration.
Reverse Synchronization Across Multiple Paths
If you select multiple paths and apply this animation, SAMSON synchronizes their playback in reverse. This is especially useful in multi-molecule systems or protein-ligand bindings, where several trajectories might interact. Playing them in reverse simultaneously allows you to rewind the interaction with clarity.
Final Thoughts
Reversing animations might seem like a purely aesthetic tool, but it brings functional benefits to molecular modeling and presentation. Whether you’re a researcher spotting artifacts or an educator building didactic material, playing trajectories in reverse in SAMSON is a flexible tool worth exploring.
To learn more about this animation effect, consult the official documentation page at https://documentation.samson-connect.net/users/latest/animations/play-reverse-path/.
SAMSON and all SAMSON Extensions are free for non-commercial use. You can download SAMSON at https://www.samson-connect.net.