Expression, using a slider value as a "length" definition

[villel62890682]

Am I missing something?

I have an expression, where I want to use a linear (ease) transition between 100 to 0, starting from a predefined marker, and having a transition length defined by a slide effect. The idea in the linear function is to define the length of the "tween" as marker+slider value.

Using this expression as source text (for troubleshooting):

endMarker = timeToFrames(thisComp.marker.key("End").time);

tweenLen = thisComp.layer("Target").effect("ValueOut_length")("Slider").value.toFixed(0);

delay = endMarker+tweenLen;

[tweenLen, endMarker, delay]

looks like minus / multiply / divide work in the var delay function, AE yields the correct result, but when I try to add, the result is endMarker value _appended_ with tweenLen value.

If I do

delay = endMarker+5

it works as it should, but then that becomes a "hardcoded" value, which takes away some of the benefit / flexibility.

Am I doing something wrong or is this a bug of sorts? Also, workarounds are welcome!

-Ville

[villel62890682]

Well, I made a new marker, and linked the "length" to that, so that works.

Still curious on the math, though.

[Mylenium]

Not sure what you expect. You are not doing a subtraction anywhere to calculate an actual time differential. All interpolation functions need a start and end parameter, not just one. The rest is just specific to debugging with text layers - mudding up your calculations with .toFixed(), which is solely meant to clip values for display purposes, will of course introduce string processing and adding a string to another string will produce a new string. You need to do the math before actually constructing your strings using math.Round() or whatever, not simply hope AE will handle this automatically.

Mylenium

[villel62890682]

The linear function was not included   The point was, as I was troubleshooting the math of my values by doing them on a text layer (just to actually see what AE was using as values), I noticed that doing

delay = endMarker+tweenLen produced 305

while

delay = endMarker-tweenLen produced 25

delay = endMarker/tweenLen produced 6

delay = endMarker*tweenLen produced 150

(endMarker value was 30, tweenLen value was 5)

And when I changed it to

delay = endMarker+5 produced 35

So, the question / observation from me is: truncating a slider value with toFixed(0) "seems" to work as expected with other basic math functions, but with an add/+ function it's acting like "string"+"string" concatenation instead of math?

And the lead-up: is that a by-product of not using math.Round to loose the decimals from the slider value?

And if so, what's the way of adding (in a math sense) to get

delay = endMarker+tweenLen to produce 35?

I'm pretty fresh to this scripting game, so this is a good learning process to me

Cheers!

-Ville

[Mathias Moehl]

By the way, instead of using text layers for debugging, it is much more convenient to throw errors to inspect any value(s) in your code.

See my tweet here

https://twitter.com/mamoworld/status/1101168951185289217

[villel62890682]

Neat trick! Thanks Mathias!

[Martin_Ritter · Accepted solution]

toFixed() is the problem here. 

From w3schools: (JavaScript toFixed() Method )

Return Value: A String, representing a number, with the exact number of decimals

So you are actual adding two strings, as assumed.

For your desired outcome, you can go with:

tweenLen = parseInt(thisComp.layer("Target").effect("ValueOut_length")("Slider").value.toFixed(0));

or more common and easier:

tweenLen = Math.floor(thisComp.layer("Target").effect("ValueOut_length")("Slider").value);

BTW: if you try to fade something, there is a script/effect called Autopacity which is driven by markers (or keyframes or what ever you like).

Cheers,

Martin

[villel62890682]

Thanks for the clear explanation. Makes total sense. And more proof that now I need to start watching my Javascript udemy course

-Ville