Blackmagic Forum

I want to insert an Expression to make this go from 0 to 1 within 1 second, and once it reaches 1 go back from 1 to 0 within another second. I would greatly appreciate your help! Thanks in advance.
Image here:

https://imgur.com/ClC3D7c

Sinus Curve (half period)

Code: Select all

: start = 0;
fps = comp:GetPrefs("Comp.FrameFormat.Rate");
if time > start and time <= (start+fps*2) then return sin((time-start)/fps*(pi/2));
else return 0;end

Linear

Code: Select all

: start = 0;
fps = comp:GetPrefs("Comp.FrameFormat.Rate");
if time > start and time <= (start+fps) then return (time-start)/fps;
elseif time > (start + fps) and time <= (start+fps*2) then return 2-(time-start)/fps;
else return 0;end

Cosinus (smooth | complete period)

Code: Select all

: start = 0;
fps = comp:GetPrefs("Comp.FrameFormat.Rate");
if time > start and time <= (start+fps*2) then return cos((time-start)/fps*pi+pi)/2+0.5;
else return 0;end

Change the start value to the frame you want to start the animation.
Do not use “Select all” to copy the code as this will add an indent.

If you don't use an expression, but looped keyframes for this, there's a chance that caching will work a little better.

+1 for loop keyframes.

The OP didn't write that he wanted to do a loop.
But if I think about it, it doesn't really make much sense to use an expression for a simple up and down...
And if you're saying it's faster to use loop keyframes, the OP should do that.
If for some reason the expression is still needed:

Code: Select all

:start = 0;
fps = comp:GetPrefs("Comp.FrameFormat.Rate");
duration = fps * 2;
loopTime = (time - start) % duration;
if time >= start then return (cos(loopTime / duration * 2 * pi - pi) + 1) / 2;
else return 0; end


Christoph, thanks so much for your elaborate reply, super appreciate it!