expression to rotate foward

[Filip Vandueren]

Hi there,

there is a way to do this all in expressions, but I think it would be difficult to tweak.

I think the easiest way would be to keyframe one rotation, including easing and a pause, then using the loopOut() expression:

for example:
set a keyframe at time 0, rotation0
set a keyfame at time 10 frames, rotation 20
set a third keyframe at time 20 frames, also rotation 20.

easy-ease the first two keyframes

now add this expression to the rotation:

loopOut(“offset”);

it’s a very handy way of looping keyframes, I think introduced in CS3.
Where a normal loopOut(“cycle”), would repeat all the keyframes continuously (so it would always reset to 0°), the “offset”-variant, actually adds the last reached value to each subsequent repetition. Just what we need here.

Bonus:

If you need to start/stop/keyframe this loop, a very versatile way to do this would be to add 2 expression controls:
a slider called “t”
and an angle called “r”

copy the keyframes and expression of rotation to the “r”-angle control.

erase the original keyframes and expression from the rotation, and add this expression to rotation:

effect(“r”)(“Angle”).valueAtTime(effect(“t”)(“Slider”));

now we can keyframe the “t” slider like this:
at time = 1s set t to 0
at time= 5s set time to 4

now the layer will start and stop rotating. The advantage of keyframing t is, you can easily start/stop multiple times, slow down or even go backwards. All using ease-ing if you’d like.

Hope that was all clear.

[Criis Daw]

Thanks for your help.

I have CS3 but i cant see loopout (offset) in he drop down.

Will it work if I type it ?

guess i’ll find out

cheers

[Jeffrey Lejune]

This was helpful so I wanted to say thanks?

One question is why you you selected the values of 0 at 1s and 4 at 5s?

Does it have something to do with the fact that the original time of the rotation from the previous explanation was 1 sec based on 30 fps?

So you get 4 rotations btwn 1s and 5s because of the 1 sec key framed looped animation. When I changed the value at 5s to 2 I got 2 rotations.

Just trying to understand the math incase I wanted to stretch things out or compress them.

[Filip Vandueren]

To re-iterate:

the angle-control has the original expression and keyframes, looping through some values, but that doesn’t do anything visual.
The expression added to rotation uses the value of slider T to look up what value the angle-control has at time=T

You can keyframe “slider T” however you like, faster, slower, start/stop whatever.

In my example,
Nothing would happen for 1 second.
Between 1-5 seconds we are reading the values the angle-control had between 0 and 4 seconds.
Because the keyframes are 4 seconds apart and their values are also 4 seconds apart, the rotation will be “real-time”, but you have a lot more options…

clear ?

[Jeffrey Lejune]

I’m getting it. Writing out comments of my observations on different iterations of the effect on duplicate layers helps.

I’m enjoying experimenting with the Angle control keyframes (timing & easing) as well as the value graph easing for the slider t control effect.

Super helpful. Thanks for the lesson!

[Jeffrey Lejune]

After a 2nd look through your 2nd explanation I also now understand why T would never work as a negative value bc the Timeline would never be have a negative value…. You’re looking for what the angle would be at a certain time based on that loop. We can’t go back past time of 0…. right? You can go from 0 to 1, etc… as well as going from 2 to 1 to 0 to get the rotation to go the other way.

but time travel to before the timeline start’s (negative value of T) isn’t possible… Hah!

[Filip Vandueren]

Values before time 0 are absolutely possible!
Just grab a group of keyframes (or a layer) and drag them to the left: they can exist before time 0 (they’re just hard to edit after you’ve put them there 🙂 )

If values exist before 0, valueAtTime() has no problem getting them. It’s just that the expression on te angle-control is creatig extra values after the existing keyframes (hence loopOut)
The angle control could have a different expression that also creates values before time 🙂

[Jeffrey Lejune]

Ahh… I see your point and thanks for the further explanation. Based on that I shifted the layer left past time 0 and then began to see results when I changed T to a negative.

The only limit at this point i see is how far back in time (left) I shift the layer or the keyframes for Angle. For example the beginning of the layer (or just the key frames for Angle) is shifted to a time of -20. I don’t see a result when manipulating T lower than -20.

So now I’m curious about your last statement:

“The angle control could have a different expression that also creates values before time :-)”

I’m not sure how to formulate that expression but would interested to know how to get it to output all the way to -infinity time. Not for a particular reason at the moment but there could be a use somewhere down the road.

[Filip Vandueren]

At it’s simplest form (assuming the first keyframe is at time=0)

if (time<0) {
loopIn("offset");
} else {
loopOut("offset");
}


This version does some more checking to make sure it works properly in all conditions:
if (numKeys>0) {
t1=key(1).time;
if (time

[Jeffrey Lejune]

Thanks for the expression script examples. I see your point how an if/then statement keeps it simple and to switch the command based on the condition.

I have experience writing AS3 OOP for web mograph with flash back in the day. Sometimes I feel like it’s hard for me to apply knowledge of simple programming over to AE expressions. Slight differences in syntax and the fact that I don’t know all what I can manipulate through code just yet. I’m slowly coming around though.

Your insights have helped!