Is there a Plug-In hook that allows direct control over position and rotation of a camera w/o keys

Question

Hi,
I'm developing a camera animation system for Cinema 4D and looking ahead to see if it's adaptable for AE.  In C4D I can create a custom camera object and control it's motion through code (no keys or visible scripting or expressions).  Is this possible in AE? 
So for example:
User creates a camera and adds something I created to attach to it (like a tag in C4D) OR I can create a custom camera object that inherits all the normal camera functions but adds additional parameters I add that auto-animates the camera (again w/o keys / visible expressions).

Answer 1

hi Chris Smith x0h00!
welcome to the forum!
thus far the fun part.
now the problem part.
what you're describing i possible, but just barely, and not without caveats.
i don't know how deep you knowledge of the SDK is, so i'll start by explaining some basic concepts.
if you're already familiar with it, the my apologies, and just skip ahead.
there are 2 kinds of plug-ins in AE:
1. EFFECTs, which are applied to layers in compositions, and are responsible for processing the image or the audio (or both) of a layer.
these effects are handed an input pixel buffer containing the image result of previous effects and masks, and are given a pixel buffer to write the output to.
2. AEGPs (After Effects General Plug-in), which are loaded on AE boot, and are kep loaded throughout the session. such plug-ins can manipulate project elements, change preferences, and add menu commands (and a host of other things).
effects can also use most of the functionality available for AEGPs, so an effect can also change project elements and all sorts of other goodies.
now something about AE's rendering logic:
all 2D layers in a comp are rendered using AE's internal 2D renderer.
all 3D layers in a comp are rendered using an AEGP of type "Artisan" (such as "Advanced 3D", as found in the comp settings).
when a render is invoked, the artisan receives from AE a transformation matrix for the camera and the transformation matrix for each layer.
now the part where it all starts to make sense:
the transformation matrix of a layer or camera is a result of the transform parameters values, including parenting layers.
the only way to change the transformation matrix, is to change the transform parameters values, or those of a parent layer.
neither an effect, nor an AEGP can change the transformation matrix. they can only change the param values.
the only exception to the rule, is an Artisan AEGP.
since it is doing the actual rendering, it can ignore the existing transformations and come up with it's own.
to pull that off you need to write a 3D renderer, and your artisan needs to be the selected one for that comp. (can be set automatically by a plug-in)
what are you other options?
1. well, you can't create a new kind of camera (or any other kind of layer), so you can only affect a regular camera.
you can have an effect or AEGP change the camera's transformation values each frame.
that would create a camera motion without keyframes or expressions, though it would be a bit strange for the user to see the camera behave that way...
you could also incorporate exisitng camera values to allow the user a adjust the camera, though that would not allow keyframing of such changes as you apply new values for each frame which would create keyframes of it's own.
you would also not get any motion blur from the camera movement, because as far as AE knows, there is no animation, just a constant value that magically changes whenever the time does.
2. there are also custom perspective views in AE. you can manipulate them over time instead of a camera. (i think you can set values to the custom views... not sure about it)
in such a case the user won't have a camera to tweak, and you'll also receive no motion blur.
3. connect the camera via parent to a null, make the null invisible (either via making that layer shy or some other shenanigans as making the layer stream hidden (i think it's possible)), and manipulate the parent null.
that's all i can think of.
i hope i didn't discourage you...