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Expression Priority

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Luka Schulz
Expression Priority
on May 23, 2018 at 2:31:26 am
Last Edited By Luka Schulz on May 23, 2018 at 1:29:55 pm

I have been having some trouble with a book rig I am making. It's not the best made file, but I was wondering if I could get a second pair of eyes to see if I am missing something.

I am using Xpresso to attach two points to the cover of a book which has been made using an FK rig. The spline whose points are being edited via Xpresso are also being edited using a pose morph tag. As of right now, I am having issues with making sure the priority of expressions is occurring correctly. I have watched a few tutorials, and read through the C4D help, but I still can't get the points to stick to the book cover as it animates open.

The file is attached, any help would be much appreciated!

12408_riggedbook0005.c4d.zip


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Steve Bentley
Re: Expression Priority
on May 25, 2018 at 4:20:30 am

First I see you are using PLA animation. The issue with PLA is that you can't do any kind of easing which looks very robotic. Instead of animating the points directly, link each point to be animated to a null through expresso, then animate the nulls - you can do any easing you want on the null animations AND every animated point can have keyframes now where ever on the timeline. They don't have to be all keyframed on the same frame anymore. The points of the spline will follow the nulls you have linked to them. If you are using R19 you can ease PLA now.

For points or objects sticking to the plane of the cover, you can link their positions (in expresso) to either the spline that makes the cover deform or to the polygon that makes up the cover itself.

For the spline, you can use a spline node and choose how far along the spline that point sits, then you can offset that point's x, y or z to get it higher or lower on the cover. When the cover moves the point will always move with it, just offset by the amount you choose.

For the cover polygon, you can get the position of that polygon in expresso (in world space) and pass it with an offset to your point,.
Or, maybe more simply, use that polygon as an emitter object for a mograph cloner; choose object and let it make one clone in the center. Even if the cloned object is not the one you want, you can then get the position of that clone and pass that to your point.

Because you are using an IK chain you can also child the object you want on the cover to one of the bones and that will position it where ever you set it to be and that object will follow along with the book deformation without actually being deformed itself. (we do eyeballs in heads like this, they are part of the iK chain and not part of the mesh or skin heirarchy)



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Luka Schulz
Re: Expression Priority
on May 29, 2018 at 6:04:26 pm

Thanks Steve for the advice. I ended up following your advice and put the end paper as a child of the IK chain. I completely forgot I could do this, and it was the easiest solution. I also ended up controlling some of the points using nulls and xpresso.

I am getting some wonky spline behavior. But I think I almost have it figured out.

Thank you very much!


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