tweening: One of the most powerful capabilities of computer animation software is its ability to fill in the logical transition, progressive changes, between two key framed attribute values of the same type, a beginning keyframe value and an ending keyframe value. This computer generation of transitional values is appropriately referred to as "tweening" which is short for in-betweening. The number of attribute value changes that the computer will generate depends on the number of frames specified in between the beginning and ending keyed frame attribute values. So for example, if we assign a keyed frame rotational attribute value of 0 degrees to an element at frame 1 and a keyed frame rotational value of 90 degrees for that same element at frame 7. Then in between frames 1 and 7 there are 5 frames and therefore 5 transitional values of rotational positioning that the computer can generate. The sequence of frames from a beginning keyframe value to the ending keyframe value of the same type, 7 frames in our rotational example, is called a segment. For any segment defined by a starting and ending key framed value pair, we can specify how the render engine will generate the in between transitional attribute values. If we just want the render engine to hold the beginning keyframe value constant until the ending keyframe value is reached, then we specify that the segment is a constant segment. This produces a “snap” or jump from the beginning attribute value to the ending attribute value. On the other hand, if we want a gradual transition in between the beginning keyed frame value and the ending keyed frame value; we will specify that the segment be a non-constant segment. By default, non-constant segments are generated linearly, which means that the rate of transition is equally spaced between values. So in our example where we have 5 in between frames between rotational values starting at 0 degrees and ending at 90 degrees, we would have attribute values created of 15, 30, 45, 60, and 75 degrees respectively. The linear rate of change is 15 degrees per frame. This is in effect an even or balanced distribution of the change in the controlled attribute. If we wanted these values to be determined differently, we could either increase the number of in between frames that make up the segment, or we could, use the TBS Function Editor to specify a different mathematical curve to be applied to control the generation of attribute value calculations. In terms of traditional animation, the variation of the function curve is the same as adjusting the spacing of the in between drawings. This is how cushioning or easing is applied to our animations generated by the aid of the computer render engine.

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