Skin Deformers & Hierarchical Animation

Computer Animation Techniques 2/5

• Games and Multimedia/3D Simulation and Animation are covered.

Skin Deformers

• Animation rigs control and deform skin geometry in several ways.
• Simple joint attachments bind skin points to one or several joints.
• Geometry deformers can be included, like blend-shape, cluster, lattice, jiggle, and wrinkle deformers.
• Skeleton geometry serves as a skin deformer by extracting and "baking" weight values onto the skin, after which the skeleton geometry can be removed.
• Muscle systems simulate muscles and that requires more sophisticated techniques.
• Muscle systems are designed with control points to maintain volume during flexes.
• Muscle systems connect to the skeleton via its hierarchy.
• Collision detection sets up muscles to slide or bulge against bones or other muscles.

Hierarchical Character Animation

• 3D objects are grouped into hierarchical structures that dictate the relationships between them and how they behave when animated.
• Diagrams of these structures are often represented as tree structures.

Tree Structure

• The root is the most dominant object, while the parent is an object with children
• Leaves are objects at the last level, while children are objects with a parent
• Siblings are objects on the same branch or level and have the same parent.
• Null parents are nodes that do not represent geometry but control several child objects together.
• Each object within the tree inherits attributes from its parents.
• Animating a selected branch is possible without animating the entire structure.
• Parenting depends on the software, requiring users to select the parent first or the children first.
• Programs may use one set of diagrams to control modeling, rendering, and animation.
• Some programs use multiple sets of hierarchy diagrams, so that modelling, rendering and animation links can be set independently.
• Hierarchical structures are important for rendering and animation stages but are created during modelling.
• Object centers or centroids are important in the hierarchical animation process.
• Geometric transformations or motion dynamics simulations are based on the positions of theses centers.
• Placements are commonly at an object's center but can be interactively placed anywhere.
• Animation rigs are hierarchical control structures to animate characters.
• Rigs contain joints and motion logic and are showcased by hypergraphs, hierarchy charts, rig skeletons of bones, and user controls to manipulate them.
• During animation, rig skeletons are often turned off, and animators pose characters with a low-resolution version of the skin.
• Animation controls' icons and color codes allow animators to recognize controls and parts faster, and can be lines, curves or complex shapes.
• These controls often include options like pivoting, lifting, twisting, and wiggling.

Motion Paths

• Usually drawn as a single path in the 3D environment, but can also be controlled with parameter curves.
• Motion paths allow the animator to quickly sketch movement that may involve several translations and rotations.
• Cameras, vehicles, humans and creatures are examples.
• These paths define the primary motion of the object, which is layered and animated with techniques like interactive keyframing and IK.
• The process involves drawing a curve in 3D space, selecting and linking a model to a path, defining timing parameters in the timeline, and adjusting speed and acceleration with parameter curves.
• Most software programs will link an object so its front is aligned with the direction of the path.
• Indicate the 'front' of the object

Bibliografia

• Isaac V. Kerlow, The Art of 3D Computer Animation and Effects, 4th Edition, Wiley, 2009.