Value in relation to keyframes

[Dan Ebberts]

I have no idea if this is what you’re looking for, but this expression will generate values between 0 and 100 as the time moves between keyframes of another property (position in this example). Before the first keyframe and after the last keyframe it just sets the result to value.


p = transform.position; // property you want to monitor
v = value;
if (p.numKeys > 0){
n = p.nearestKey(time).index;
if (p.key(n).time > time) n--;
if (n > 0 && n < p.numKeys)
v = linear(time,p.key(n).time,p.key(n+1).time,0,100);
}
v


Dan

[Aaron Pozzer]

hey Dan. thanks for the response. so this KINDA works, but not quite.

i have my null object. lets say it has 4 position keys to its animation, and it just outlines a simple path. lets say the 1st key of this animation is on frame 10.

when i start at frame 0, the expression calculates the value i entered: -50 (i want the line to come closer to the camera, hence the negative value). as i scrub forward towards frame 10 (the first key), nothing happens. when i hit frame 10 the value is set to 0. as i keep scrubbing towards the next keyframe the value climbs all the way up to -50 and when it hits the next key it resets back down to 0. over and over for as many keys as there are in the animation.

so, this isnt the desired effect. this creates steps kinda, with the -50 z value always being right before the next key is reached. what i was after was that -50z was always in the middle of any 2 keys. so when its ON a key, its 0, and when its between any 2 keys its trying to get to -50 (or whatever value). the goal is to create arcs with the highest point of the arc being between any 2 keys.

i suppose using linear would give a series of pyramids/steps rather than arcs. perhaps ease is better suited for this expression?

anyway, does that make more sense? is it possible?

[Dan Ebberts]

Something more like this then, probably:


p = transform.position;
offset = 0;
if (p.numKeys > 0){
n = p.nearestKey(time).index;
if (p.key(n).time > time) n--;
if (n > 0 && n < p.numKeys){
t0 = p.key(n).time;
t1 = p.key(n+1).time;
d = t1 - t0;
t = Math.abs(time - (t0+t1)/2)
offset = ease(t,0,d/2,-50,0);
}
}
value + offset


Dan

[Aaron Pozzer]

thats the ticket! worked great. if i wanted to be SUPER picky id ask if there was a way to increase the offset for the further away keys are. like if keys are more than 10 frames apart offset by ____, if more than 20 frames apart offset by _____… or some automatic scaling factor that would just do it automatically.

but ya, its fine now as it stands unless you wanna try and solve that one too.

thanks dan!

[Dan Ebberts]

This should do it. Adjust variables nom and peak to get the relationship you want.


p = transform.position;
offset = 0;
if (p.numKeys > 0){
peak = -50;
nom = 10; // frames
n = p.nearestKey(time).index;
if (p.key(n).time > time) n--;
if (n > 0 && n < p.numKeys){
t0 = p.key(n).time;
t1 = p.key(n+1).time;
d = t1 - t0;
t = Math.abs(time - (t0+t1)/2)
offset = ease(t,0,d/2,peak*d/timeToFrames(nom),0);
}
}
value + offset


Dan

[Aaron Pozzer]

awesome dan!

a question about ease. my ideal curve for the line all this stuff is controlling would be this sort of shape…

https://www.unifycommunity.com/wiki/images/e/e8/Mathfx-Bounce.png

…where the in and out points are hard, and the arc in the middle is smooth. is there a command like ease that will give this shape instead of the smooth shape of ease?

[Dan Ebberts]

Maybe you just need to use easeOut() and easeIn() instead of ease(), like this:


p = transform.position;
offset = 0;
if (p.numKeys > 0){
peak = -50;
nom = 10; // frames
n = p.nearestKey(time).index;
if (p.key(n).time > time) n--;
if (n > 0 && n < p.numKeys){
t0 = p.key(n).time;
t1 = p.key(n+1).time;
d = t1 - t0;
t = (t0+t1)/2;
if (time <= t)
offset = easeOut(time,t0,t,0,peak*d/framesToTime(nom))
else
offset = easeIn(time,t,t1,peak*d/framesToTime(nom),0);
}
}
value + offset


I also corrected an error in the previous version where I was using timeToFrames() instead of framesToTime().

If this doesn’t give you what you want, you may need to implement your own quadratic or cubic easing function.

Dan

[Aaron Pozzer]

hey Dan. thanks for making the above adjustment. i didnt even notice till just now when i came here to ask another follow up question. so, im trying to be proactive and figure stuff out for myself, but not having much luck.

im trying to modify the 1st expression you posted (since its the simplest) to serve as a general purpose monitor for the same property im trying to watch and drive the Z position of that null.

i want it to be able to drive things like opacity, birth rate, etc, on any property i want, so things will all turn on/off in relation to those keys, and i only have to animate one channel basically.

but!… the modification i was trying to make would seem to only require the time of the 1st and last keys. if i wanted to fade something in at the 1st key, and then fade it out at the last, any keys in between wouldnt matter.

i had a look at the options available. im not sure key(index) would work, cause the # of keys might change… so only the 1st key would be the same. nearestkey would use them all i think, so thats no good, and key(markerName)… well im not sure on this one. i dont know how to set a marker name for a key, unless it means just a regular marker with you set with the * key?

then i guess the other problem would be, once it hits the 1st key and the opacity is triggered to raise from 0 to 100, does that happen instantly? i guess so, unless you tell it otherwise… so i wouldnt know how to build in a frame buffer as it were, so it comes on over 5 or 10 frames.

so if you were to modify the above, im not sure if needs all the fancy easing and such. these just need to turn stuff on.

thanks again Dan!

[Dan Ebberts]

This should fade from 0 to 100 at the first position keyframe and 100 to 0 coming into the last keyframe. It won’t do anything unless there are at least two keyframes:


p = transform.position;
fadeFrames = 10;

if (p.numKeys > 1){
t0 = p.key(1).time;
t1 = p.key(p.numKeys).time;
t = framesToTime(fadeFrames);
if (time < (t0+t1)/2){
ease(time,t0,t0+t,0,100)
}else{
ease(time,t1-t,t1,100,0)
}
}else{
value
}


Dan

[Aaron Pozzer]

great Dan! perfect as always. much appreciated.