3D Stroke Expression

[Lord Scales]

I asked Dan about this and it seems to be impossible because masks don’t give us a position coordinate. I hope, in a future version of AE Adobe will think about this.

And I think 3D Stroke could give a coordinate about the position of the stroke “emitter”, but until then, I am going to use Write-on effect when I need coordinates.

[Brennanc]

I’m actually working on a project right now where this is the main effect needed over about 25 shots. The solution that i’ve found is not in AE but using a 3d package (i use 3dsMax but i’m sure that most can do this).
So here it goes my friend…
1. Make your path in 3dsMax. in my project i’ve had to bring footage in on the background to match the camera moves (manually, nothing fancy).
2. animate your stroke in 3dsMax and create a camera to view it. This can be accomplished with a cylinder and the path deform modifier using the path for refrence.
3. Create a second camera and use the same path as a refrence for the camera’s animation. Basically, animate the camera along the path using the motion tab in 3dsMax. this camera will not be used to render the path, just to get the zdepth info from it.
4. Render camera 1 out as a 16bit .rpf sequence with all the options to get the path animation with alpha channel.
5. Now hide everything in the scene and render camera 2 out as an 8bit .rpf sequence.
6. In AE import both the .rpf sequences and bring them into your comp.
7. For each .rpf sequence, use the keyframe assistant to import the .rpf camera information.
8. Now use the info from your camera1 sequence as the active camera in AE and the info from camera2 as your effects position info.

This can be used to drive particle effects, lights, or any other effect that requires extensive 3d positional data to be matched to a camera. Sometimes you just have to think outside the box that AE came in 🙂
Good Luck!