Flash MX 2004 Games : Art to ActionScript

Flash MX 2004 Games
Figure 4.9 The main body for the cat model
position of the points in a mesh. Lightwave can decide which points a bone modifies on the basis
of location. A point will be controlled more by nearby bones than by distant bones. This method
works for some meshes but can cause errors in character animation as limbs are so close together
that the left thigh bone may influence the right thigh bone. Another technique is to create a
definite relationship between a bone and certain points in the mesh. To set up a character to use
bones in this way you create vertex maps; a vertex map is simply a list of vertices with each vertex
getting a specified weight. A weight of 100 per cent means total control over the vertex while
a weight of 50 per cent means partial control. In this way you can control exactly which bone
adjusts which points and errors are eliminated.
Animating the character
Once the character is set up to use bones you have control over each part of the mesh. Another
useful feature of most computer animation programs is the use of Inverse Kinematics (IK). This
is just a fancy name that means that you can move the body but the feet will stay put. When
animating a character, IK is a very useful feature and well worth setting up. You create a Null
object (an object which is used for animating but contains no geometry so it is invisible to the
camera) and this will become the target for the feet. Using IK, the feet will move to the target
and can be made to rotate towards the target. The cat character uses IK on the feet, tail and eyes.
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