Horizontally Rotating car done with expressions

[Darby Edelen]

Your solution will require a pre-comp with your car sequence in it, and time remapping enabled on the pre-comp in your parent comp. From there you’ll need to determine the angle from which the camera is viewing your layer with some vector math, perhaps using a derivative of Dan Ebberts’ Auto-Orient to Camera expression. Try applying his expression to the Y-Rotation property:

delta = toWorld(anchorPoint) - thisComp.activeCamera.toWorld([0,0,0]);
radiansToDegrees(Math.atan2(delta[0],delta[2]));


Then you need to go to the proper frame in your pre-comp for that angle of view, so try applying this to the Time Remap property:


offset = 0;
reverse = 1;
numFrames = 50; //if your pre-comp is exactly the same length as the number of frames in your rotation sequence then you could try using numFrames = timeToFrames(duration);
deg = transform.rotationY; //this requires the previous expression be already applied to the Y rotation
(offset + reverse * deg * numFrames / 360) % numFrames;


The offset variable above would be used to offset the initial orientation of the car, it might be worthwhile to link this to a Slider expression control. The reverse variable should be switched to -1 if the car appears to be rotating in the wrong direction.

I haven’t had an opportunity to test any of the above in AE, so let me know if there are any problems. Also, I think you were asking for a 2D solution… if you leave everything 2D in your comp except for the car, then it should interact with a camera in the way that you desired. At least that’s the way it works in my head 🙂

I may test this out tomorrow at work and post some refinements if necessary.

Darby Edelen

NVIDIA
Santa Clara, CA

[Darby Edelen]

[Darby Edelen] “offset = 0;
reverse = 1;
numFrames = 50; //if your pre-comp is exactly the same length as the number of frames in your rotation sequence then you could try using numFrames = timeToFrames(duration);
deg = transform.rotationY; //this requires the previous expression be already applied to the Y rotation
(offset + reverse * deg * numFrames / 360) % numFrames;”

Well, I still haven’t had a chance to test it, but the above expression is wrong. It needs a call to framesToTime() on the final value:

offset = 0;
reverse = 1;
numFrames = 50; //if your pre-comp is exactly the same length as the number of frames in your rotation sequence then you could try using numFrames = timeToFrames(duration);
deg = transform.rotationY; //this requires the previous expression be already applied to the Y rotation
framesToTime((offset + reverse * deg * numFrames / 360) % numFrames);

Sorry for the mix up 🙂

Darby Edelen

NVIDIA
Santa Clara, CA

[Darby Edelen]

Unfortunately the above expressions definitely don’t get the job done. I guess I can try and play around with it some more, but it looks like I need to rethink the way I’m approaching the problem.

Darby Edelen

NVIDIA
Santa Clara, CA