Knowing how motion points work can be essential to properly animating objects along a path.
When you want to animate an object along a path, it’s best to use a Peg in conjunction with the Motion Tool. This way, you will be able to see the path your object follows, and make adjustments to the shape of this path. Motion Points are created when you set keyframes along a path, and by moving these points you can change the shape of your path, as well as the timing of your animation.
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There are two types of Motion Points you can create when animating with the motion tool. Keyframes are used to lock a drawing in position at a specific frame in time. Just moving your object with the motion tool will create a keyframe. You can also add a Control Point to your motion path. Control points are different than keyframes, as they will modify the shape of the path, but not change the timing of your animation. On your path, a keyframe will be red, while a control point will be green. Add a control point with the Motion tool by holding down the [Shift] key with the cursor over your path.
The shape of the path between motion points will greatly impact your animation. Changing the tension of a motion point will help with just that. Selecting a motion point in Camera view will bring up its options in the Properties window, where you can change a point’s tension by dragging the Tension slider. -1 being the lowest and 1 being the highest. (There are also Continuity and Bias settings you can change. See the User Guide for more information on these settings.)
The basic curve below (on the left) has four keyframes with a default tension of 0, and shows a smooth path for this ball. In the example on the right however, the tension of the 2nd keyframe was set to 1 while the 3rd was set to –1. This results in a different path altogether. Depending on the movement you are trying to achieve, you may have to adjust one or all of the motion point properties to get the desired shape for your curve.
The following example of a bouncing ball, animated with keyframes, uses two different types of tension settings. At the point of impact, where the ball smashes into the ground abruptly then flies off in the opposite direction, we need a sharp angle. The default tension of 0 was changed to 1 to achieve this effect.
But at the top of the curve, where the ball is floating through the air, a smoother curve is required. In this case, the tension was left at 0. It would be impossible to achieve a smooth curve if you were to use a tension of 1.
The default tension of a motion point is 0. You can, however, modify this in the Preferences window, in case you would prefer the default be set to something else. In this window, set the default tension for motion points to be whatever is most logical for your style of animation.