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Week 24: Volumetric FK Scaling and Reference Retargeting

Got some pretty exciting results this week after experimenting with scale. Maya scaling works in UE4 and Unity since segment scale compensate is turned off and scaling is uniform (no shearing), woo! Here is an image explaining the main gist of the system.

To explain what's going on above, first a matrix is composed from the translate of the joint that will be scaled. The reason for composing a matrix out the translate instead of using the world matrix is to remove any cycling since the end result will be fed into the joint's scale attribute. Then, the composed matrix is multiplied by the parent matrix and then decomposed to get the world position. The world position of the child joint or the control driving the child joint is plugged in to a distance node. Then distance is divided by the rest/initial distance. The initial distance is the distance of the two joints when they are bound to the mesh. The inverse of the result of the current distance is divided by the rest distance (inverse is just 1 divided by X), and plugged back into the scale of the first joint. When everything is plugged in, we should see the first joint being scaled volumetrically whenever the distance of the two joints changes (usually by translation). There is an example of this system towards the end of the GIF below.

I moved the node system pictured above into the Piper FK controls compute method via a C++ plug-in since almost all the FK controls could benefit from it. Other cool scaling features of the FK chain are full chain scaling, or individual joint scaling via the inner controls as seen in the GIF above.


Another Piper rig feature that will help tremendously with animation work is the live retargeting of animation. By storing the a few of the joint's bind data as attributes, such as its world matrix, Piper can offset the controls when a mesh reference is replaced. As long as joint and attribute names remain consistent, Maya will keep its connections. Example below:

Animation on the Blobber is retargeted onto the Mooer just by replacing the skinned mesh reference. Maybe I won't have to animate that much... right?