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Saturday, December 6, 2008

Muscle Update

Below are my paper notes on more Maya Muscle Tools:

There are many Paint Weight Attributes but there are a few main attributes that control overall movement of the skin geometry reaction to muscle and capsule:

Sticky: Amount 0-1 that controls how much each vertex sticks to the corresponding muscle.
Sliding: Amount 0-1 that controls how much each vertex slides to the corresponding muscles and capsules.

Amount 0-1 that controls how geometric skin is affected by gravity and speed of underlying capsules movement. Feedback only achieved after animation of capsules.
Cycle: Amount 0-1 that acts as a multiplier controlling how fast jiggling starts.
Relax: Amount 0-1 that controls how fast jiggling stops.
Wrinkle:Amount 0-1 that can be painted to encourage vertices to come closer together forming wrinkles.
Self Collisions: 0-1 Amount that helps Maya know where to watch out for geometry hitting itself.

Bone Conversion Issues:

Already mentioned, this toolset can use existing bone tools from Maya to convert existing bone objects into Capsules for muscle use. The process then continues regularly to add muscle objects to the newly converted capsule objects.

A downfall though is that pre-existing bone objects must have correct axis-orientation with one another. This is because when one creates bone chains it is possible to rotate a bone object out of alignment with its parent. Bone axis of rotation is independent of World Space axis.

In Maya, all bone axis at default point the X-axis towards the next child in the bone chain. If this isn’t true when bones are converted into capsules, it will cause random capsule creation and irregular results.

Fortunately this is easily remedied for the artist that is trying to convert Maya Bones into Maya Capsules by re-orienting the Maya bones so that they all follow the same axis of rotation before they are converted to Muscles. To do this Use the Re-Orient Tool in Maya’s Animation Tool.

Other tools of convenience are a Mirror Muscle/Capsule/ and Paint weights tool, which comes in handy for creatures and characters that are symmetrical. The artist can complete one side of the character and simply tell the computer the axis of reflection to mirror data over and apply it completely to the characters opposing half. This will speed up time and creation of rigs exponentially and will prove instrumental in future projects.

Another extremely powerful tool is the ability to attach muscles end affectors to other muscle objects. This allows for muscle stacking. Which in the face is crucial because there are layers of muscle that interact with each other between skin and skull.

All of these tools make for a very high set up time, but more importantly a toolset that is versatile enough to create an anatomically correct muscle driven rig for a human face.

Below is a simple arm rig to test some of the principles.

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