Main Form Animation Controls

Figure 4.2: The Main form animation controls

Each molecule in VMD can contain multiple sets of atomic coordinates, which may be animated to show its motion over time. The coordinate sets can come from a molecular dynamics simulation, or simply multiple versions of the same molecular structure. The main form contains controls for animated playback of these trajectories. The controls contains several buttons which act like the buttons on a VCR or DVD player. The buttons provide a way to play the trajectory, step forward, stop, go to a specific frame, and go to the beginning or end. The status and frame counters shown in the animation control reflects the state of the top molecule. Commands entered via this control, however, affect all active molecules, not just the top molecule, allowing concurrent animation of multiple molecules.

Animation Speed

The rate of playback can be controlled in two ways. The Step control changes the animation step size. By default, the frame step is 1, so each step of the playback increases (or decreases) the animation frame number by one. If the frame step is 5 then the animation proceeds five times faster because only a fifth of the frames are shown. The Speed slider at the bottom of the form also affects the playback speed. Internally, this controls how many screen updates are needed between each step. By default, the slider is at the far right indicating that one step is performed for each screen redraw. Moving the slider to the left increases the minimum time required between updates.

Jumping to Specific Frames

The start and end buttons are used to simplify the comparison between the initial and final structures. The start button resets the current animation to the first frame, and end jumps to the last frame. If you need to jump to a specific frame, enter the frame number in the frame counter text area next to the start button and press enter. One thing to bear in mind is that the frame number starts at 0, so to jump to the 5th frame, you must actually enter 4 here. The animation controls are all relative to the top molecule.

Looping Styles

When the animation is playing forward and reaches the end of the data available for the top molecule, one of three possible actions takes place, as specified in the style chooser. The default is `Loop', which will reset the active molecules to the first frame and continue playing forward. `Once' will stop the animation when it reaches the last frame, and `Rock' reverses the direction of animation. The actions are symmetrical when the animation is playing in reverse.