Inverting the animation path?

Hey all,

I'm doing the VFX book tutorial and I'm trying to knock out the Practice Exercise on page 107. In question 2, it says "Use a transform node to keyframe Dr Jones so he follows the same path as the biplane, but inverted."

It's easy enough to just drag keyframe nodes around, but I've been trying to do a direct mirror invert using a 180 degree X Rotation in the Modifiers section. When I do that, Dr.Jones.tif follows the inverted path, but the Paint Node refuses to add any stroke to said path. Thoughts?

Hi,
have you ever solved this issue?

I'm currently working through the training material and got stuck at the exact same spot.
The mirror invert doesn't work for me as it also inverts the path of the biplane. Instead I managed to have Dr. Jones follow the inverted path by using an expression (Point()) for the center of the image.
I copied the paint node to create the blue path, but I do not get it to follow per displacement modifier.
I either have the blue path on top of the red path or inverted, but then without animation

When I look at the image in the training pdf it looks like the red and blue paths are not exact mirrored versions of each other. Rather the blue path seems to be created manually in the same way as the red path. But that beats the purpose of adapting everything automatically once you change a parameter of the original animation.
I wish they had included the solutions to the exercises in the backup folder.

Otherwise the training material is excellent.

I, too, was thrown off by this exercise. I believe all of us were reading something extra into the exercise instructions that was not intended...

When it says, "add this silhouette to your plane comp and have it follow an inverse path of the plane’s path", I think we all assumed that intent of the exercise was either to duplicate and modify the existing Transform (via a rotation or a similar approach) in order to invert the path; or, that we were to leverage the existing Transform and use some sort of mathematical expression to invert the path. I spent much of my afternoon attempting to do this without success.

However, the exercise does not intend for you to use the existing Transform, nor a modified duplicate thereof. Step #2 says, "Use a transform node to keyframe Dr Jones...", not "the transform node...". Look closely at the image that shows "how your composition might look". Notice, the blue path is not an inverted copy of the red path. The crests, troughs, and widths of the wave forms do not match.

The exercise intends for you to create a new Transform node; and to repeat the steps tutorial in order to: keyframe a similar inverted path, and to publish the path of the new Transform for use with the blue Paint node. It is simply reinforcing what you've learned by making you repeat the steps; it does not intend for you to extend, enhance, or extrapolate from the process.

Note, however, once you've created the new Transform node, you can copy-and-paste the existing Paint node, and simply change its color to blue, connect its shape animation to the newly publish second path, and connect its linked displacement value to the same parameter of the new path. Doing this obviates only the steps to format the style of the line; but, I found that method to be faster and simpler.

I know this thread is a couple months old; but, when I read it a few weeks back, I tagged it in the back of my mind. I did the exercise today, and wanted to provide my findings. I hope this follow-up will eliminate potential consternation for those following after us.

Thanks Drew,
that makes completely sense.

Harald

Hi

I landed here looking for the same answer. Also a beginner following the same tutorial. I have subsequently found a way to base the "blue" path on the "red" path but inverted. If you're interested, this is what I did.

To create an inverted path:
Create a new background node, solid colour, with Red, Green, Blue and Alpha all set to zero.
Highlight Background1 and insert a new paint node. Do the same as Paint1, create a polygon with 2 points which connects in the same way to the Path1. This time set the path colour to blue.
Highlight the paint node just created, and create a transform node. In the transform node, click on flip vertical. This inverts the blue path. So now any change to the "Red" path has the same but opposite effect to the "Blue" path.
Connect the output of this transform node to the output of the merge node before the FilmDamage node

To animate DR Jones along the "Blue" path:
Add the Dr Jones media to the work space. Name it DRJONES.
Highlight DRJONES and add a transform node. In the transform node, add an expression for Centre X and Y. Type = in the Center X field and press enter. Then in the expression field place this:
Point(Transform1.Center.X,1-Transform1.Center.Y)
Connect the output of the transform node to the output of the last merge node.

An alternative would to publish the inverted path and let DR Jones follow that, if that's possible.
There are probably many other sophisticated ways of doing this. I'm just a beginner so happy to be shot down.

Greg

Hiya,

I followed your instructions Greg RG. Great work! Did you learn how to write that expression in the transform node somewhere online, figure that out through experimentation, or know how to write that kind of expression from experience in coding/maths?

Cheers,

EJC

Hey Daniel, Glad you found it useful. I am an old Guy with 40 years programming experience. I am a real beginner on DaVinci Resolve but the years of programming translate well into many of the facets of DaVR - like understanding nodes, video formats etc., and working with formulas which is an uplift from programming functions. I'm still a rank beginner, though. Thanks for the reply
Greg

Then in the expression field place this:
Point(Transform1.Center.X,1-Transform1.Center.Y)

I logged in specifically to say: Greg, you sir are a goddamn beautiful human being. Thank you so much. You have no idea how long i've been banging my mathematically-challenged brain against the table for.

Hey Tim, glad it was useful. I know what its like, I have deep in furrows in my brow from head banging as well. rgds, Greg

Hey everyone, a bit late to the party, but i did find a way to do this without expressions. not my strong suit

1. Dr jones, duplicate the transform & in the modifiers, change x rotation to 180.

2. Paint stroke, duplicate, remove from path. Add new BG node with alpha set to zero, attach to bg of paint node. Then take output of paint node into a matte control node as a solid matte and BG. Output of that into a transform node & flip. Into a merge node directly after the first paint node. Don't forget to modify with your new flipped transform.

Any changes made to the Keyframes in the Dr Jones Transform (if you want to) will effect the painted line accordingly.