View Full Version : Expressions Able To Affect Graph Keyframes?

05-01-2005, 10:45 PM
Before I start doing all sorts of tutorials and reading whatever documentation I can get my hands on, can anybody tell me if it's even possible to affect single keyframes of a graph using expressions? What I have in mind is to set up a Null or a slider to move a single keyframe (a rotation extreme)in a motion graph, while keeping the in/out curves that I've set up manually intact. The effect will (hopefully) be sometihing like a wing flapping down to 70 deg. below horizontal sometimes and, say, 40 deg below other times, while keeping the wing speed and overall motion intact. Is such a thing even possible, or am I going to have to find another way to do it?

05-02-2005, 11:14 AM
Maybe if I phrase the question differently.....

Is there an Expression function I can use to limit a graph while maintaining the tangency settings?

In other words, if I use "Clamp" to affect my rotation, the rotation "freezes" when it hits the max value, then unfreezes when the graph gets below the max value. I'd like to maintain the continuity that the higher-value keyframe setting had, while settingit's value to the clamped figure. Is there an expression function that will do that? All the ones I've tried so far have the clamping effect.

05-02-2005, 12:06 PM
OK, I have a workable, if baroque, solution.
It involves using the "Value Crossfader Type A" Expression, and three nulls.

What I did was to create two motion graphs, one for null #1, and one for null #2. I used Position.Y as the channel, but I think it's pretty arbitrary what channel input you use. They both had beginning and end values at 0, and #1 had a keyframe at frame 20 of 0 as well. #2 has a keyframe of 360 at frame 20. I then assigned the Expression to fade between the two graphs as a percentage based on the numeric value of the Y-position of the 3rd null. At 100, the graph for null #2 was in control, at 0, the graph for null #1, and any position in between was a proportional value. I gather I could use a slider for this as well, but I just wanted to check its functionality first. This was then fed to the rotational value of my object.
Thus, by setting the Y-value of one null, I can interactively control the extremes of the rotational arc of a third object, while keeping the incoming and outgoing curves intact for smooth motion.

If anybody has a more elegant solution, I'd love to hear it.