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I have following problem: I am trying to tweak the speed of a Math.sin function. Therefore I need a variable that incerements over time with a combination of a keyframed speed variable.

Sounds complicated, I know.

Let's say I am using the global time variable and convert it with the timeToFrames() function I get an integer value for each frame.

myTime = timeToFrames(time);

This leads me to a value of 1 for Frame 1, a value of 2 for Frame 2, and so on. But what if I want to manipulate the increment. For example:

//speed (gets tweened from a certain value range,for example: 10 - 1)
s = (some connected slider here)

myTime += s;

If I have a speed of 10 at Frame 1 I would get a value of 11. If I have a speed of 8 at Frame 2, I would expect a value of 11 + 2 + 8 = 21.

What I get is only 2 + 8;

So I need to store the value at every frame. Is this possible?

Please help.

  • You can calculate the value by creating a new variable var x = 10; or dynamic: var x = value and use the addition assignment operator += (x += 5), but this is just the shorthand of x = x + y. – p2or Sep 22 '15 at 14:09
  • yeah thats what I am doing at the moment. The problem is, if I add 10 to x at frame 1 I get for example 11. On frame to it should automatically incremnt by 1 again + the value of my choice. But on frame 2 after effects already forgot about my 11 and it simply goes on wiht a value of 2 plus my variable. You know what I mean? – Marten Zander Sep 22 '15 at 14:12
  • Can't test it at the moment... but what about creating an additional var lastframe = yourCalcValue; or calculate both values from the current and the last frame at once? – p2or Sep 22 '15 at 14:22
  • @poor sounds interesting – Marten Zander Sep 22 '15 at 14:23
2

You can loop over the range of frames from the start of the comp to the present and calculate the value along the way.

function myFuncf(theTime){
 //whatever the function you're using to create the value, e.g.
 t=theTime + s.valueAtTime(theTime); //s is the slider
 return t
}

firstFrame = timeToFrames(inPoint); //if you want it to calculate
                                    //from the beginning of the comp
                                    //change this to 0, or maybe 1?
                                    //I'd check but I'm rendering ATM

mytime=0; //initialise the mytime variable

currentFrame = timeToFrames(time);
for (int i=firstFrame; i <= currentFrame; i++){
  mytime += myFunc(framesToTime(i)); //need to convert frames back into seconds
}

after the loop myTime should be the sum of the results of function myFunc from all the previous frames up to and including the present one (I'm not 100% sure if the loop should end when i < cf or i <= cf, you might want to test).

note first time I posted this there was a mistake. Where I called the function I was giving it frames (from i the loop variable), but it uses valueAtTime which expects time in seconds, so you need to convert: mytime += myFunc(framesToTime(i));

If you have a long comp or this is applied to lots of layers, this expression may become slow to evaluate and cause lagginess. If it becomes a problem convert the expression to keyframes.

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