Invert 1 Key Frame Value With A Checkbox?

[Paul Roper]

Put this in your rotation expression:

if(effect("Reverse animation")("Checkbox")==1)
{
-value
}
else
{
value
}

[Paul Roper]

….although this will invert all your keyframes, unless you keyframe the invert control, ie. 1 frame before your second keyframe, set “Reverse Animation” checkbox to OFF, then on your second rotate keyframe, set it to ON.

Obviously there will be only 1 frame from inverted to positive; the movement will not be smooth. But that’s what you get with checkboxes – they’re either on or off.

[Chad Gilmour]

Sweet! I got it to work by eliminating some of the carriage returns around “-value” and “value”.

I think this “if/else” type of expression might open me up to some new things.

Is there a place online that explains things like difference between using “( )” vs “[ ]” vs “{ }” and why you needed to use 2 equal signs instead of 1?

Thanks again, I really appreciate your help.

[Chad Gilmour]

My second keyframe value is 0 so no checkbox keyframing required. Good to know though! Is there way to only select a specific keyframe with markers or something?

[Paul Roper]

Dan Ebberts (you’ll see a LOT of him in this expressions forum!) has a great site:

https://www.motionscript.com/

As for the brackets:

() is normally used like you would in ordinary maths, eg. (2*3)+10 is not the same as 2*(3+10)….or as part of After Effects’ syntax of naming properties.

[] is normally used for arrays, eg. the position property has two or three variables: [x,y,z] so to access just the x, you’d use: transform.position[0]
to access the y, use
transform.position[1]

{} are for Javascript-type things, such as if…then statements. In the example I provided, the {} isolate the different things, eg:

if (john_age > fred_age)
{
everything within
these curly brackets
happens if
john is older than fred
}
else
{
everything in here
happens
no matter
how long
it
rambles
on
for until you
get to the close
curly bracket
}

Hope that helps…I’m just kinda rambling while my Mac has a prolonged spinny-ball-of-death moment. Ah – it’s back to life!

– Paul

[Paul Roper]

….oh and sometimes, when copying scripts from t’internet, it might help to first paste them into a text editor (TextEdit, Notepad, etc) and turn off all the formatting to get rid of any web/html/formatting weirdness, then copy from this and paste into after effects.