Thursday, 23 February 2012

Softimage - fcurve interpolation types

In an attempt to better understand the fcurve editor, I'm going to be doing some far more basic examples of how the curves effect the timing/speed. To start with, looking at Softimage's preset interpolation types:

The three balls all have keyframes set at the same points. Although they reach the start and end points at exactly the same time, the way in which they reach those points is very different. In other words, the speed is the same, but the timing is different.

The first ball uses the default "spline" interpolation. Each keyframe will be connected by a smooth curve or "spline" (tried looking up what a spline actually is, but it made my brain hurt), eases into or out of each keyframe, creating very smooth and organic animation.

The curve shows how the ball gradually accelerates out of the starting position, then gradually slows into the second keyframe (the highest point on the graph represents the furthest distance travelled). It then slows out of that pose and comes back in the opposite direction, easing back into the starting position.

The second ball uses the "linear" interpolation type, which as the name suggests is a constant rate of motion with no "cushioning." Objects with a linear interpolation will have their keyframes connected by straight lines, terminating in sharp points at each keyframe, representing a constant speed and sudden changes at each into and out of each keyframe. The result is very mechanical and robotic, potentially useful in animating cameras or lights where such organic motion as offered by spline interpolation isn't always needed.

This ball's rate of motion is steady and unchanging. It starts and ends at exactly the same speed with no acceleration at all. The change of direction is very sudden and sharp with no cushioning from one keyframe to the next.

The last ball uses a "constant" or "stepped" interpolation which keeps the keyframe's current values (position, rotation etc) stationary until the point of change, at which point it will "pop" or "snap" straight to the next one with no in-between movement. This is primarily useful for blocking out the keyframes of an animation without any pesky inbetweens, making it easier to check that the flow from pose to pose is correct. It could also be useful for camera or lighting cuts!

You can see from the graph that the ball's x position remains at the same level until frame 25, where it suddenly snaps upwards to the far right of the screen (highest point on the graph). Again, it remains in this position until frame 25, where it suddenly pops back to the lowest point on the graph - the starting position.

It's mostly the spline interpolation I'm interested in at this point. I certainly understand the principle of how it works, I think it's just going to take a lot more practice to get my brain used to interpreting the curves as speed and movement. I'm going to use the same setup as above - three balls moving at the same rate - but altering the fcurve for each one so that I can better compare the results and, hopefully, start to understand how certain timings "look" as a curve.

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