keys on expressions

[Nibbler]

I didn't know that its possible to set keys on expressions , like in example expression in "ty" on sphere: sin($FF) , I set key for some frames and then set key as: "sin($FF) * rand($T *30)" (or anything) and it works, amazing hehe

expr_keys.hipnc

Edited March 11, 2013 by Nibbler

[Annon]

More likely is your keyframe has overwritten the expression...

[Cuckon]

I had the same feeling as Nibbler at the first time, and it seems true expression keyframes. type -$FF at frame 1 and keyframe to $FF then open the channeleditor, it shows the evaluated result curve.. Amazing.

[edward]

More likely is your keyframe has overwritten the expression...

To clarify, "expressions" (aka "function") in Houdini are owned by "keys", and "keys" in turn are owned by "channels". All keys in Houdini have a built-in "expression" which is used for evaluation until it hits the next key. For frames before the first key, the first key's expression is used. For frames after the last key, th last key's expression is used.

When you type in an expression, Houdini just creates a channel with a single key at the global animation start frame ($FSTART), using the expression you typed as its "function". Since there's only one key, then that expression is used for all time. Nothing stops you from adding more keys, nor changing the default bezier() keyframe expressions to anything else.

I think this animation structure predates Houdini itself and was there since at least PRISMS?