Interping To Keyframes
From RoboBlitz Editor Wiki
Many people are familiar with claymation. The animator adjusts clay sculptures ever so slightly and takes a picture each time. When enough frames are run together the sculptures seem to move. This is an arduous process and approximately 30 photographs need to be taken for each second of animation. Each adjustment between frames has to be ever so slight.
3D Animation in computer games works in a similiar fashion. Each frame the computer adjusts a 3D model to a new position and renders the frame accordingly. Unlike claymation, the computer can be responcible for doing all the small adjustments.
Lets say we want to animate a simple truck driving down the street (but lets not worry about turning the wheels). In claymation you need to move the truck forward ever so slightly 30 times, taking a picture each time.
How Keyframes Work
In computer animation, you can set two key frames. One with the truck at it's starting point and one with the truck at it's ending point. The computer can "interpolate" (or "interp" for short) the truck's position based on these two keyframes. All it needs to know is how much time passes between the two keyframes (that way it knows how fast to move the truck along it's interpolation).
Lets say we want the truck to turn the corner after the second keyframe. This is a simple example, so I don't mind if the truck in place. So the third keyframe is 2 seconds after the second keyframe (the one where the truck is at the end of the street), and in the third keyframe the truck is rotated 90 degrees so it's facing down the cross-street. The truck will now drive down to the end of the street, stop, and start turning in place 90 degrees.
The fourth keyframe can be down the cross-street a little bit, and the truck will start moving again once it's done turning.