Programming 3D animations?

Question

What are the different ways to handle animations for 3D games? Do you somehow program the animations in the modeler, and thus the file, than read and implement them in the game, or do you create animation functions to animate your still vectors?

Where are some good tutorials for the programming side of this? Google only gave me the modeler's side.

Answer 1

In production environments, animators use specialized tools such as Autodesk's 3DS Max to generate keyframed animations of 3D models. For each animation for each model, the animator constructs a number of poses for the model called the keyframes, which are then exported out into the game's data format.

The game then loads these keyframes, and to animate the model at a particular time, it picks the two nearest keyframes and interpolates between them to give a smooth animation, even with a small number of keyframes.

Animated models are typically constructed with a bone hierarchy. There is a root bone, which controls the model's location and orientation within the game world. All of the other bones are defined relative to some parent bone to create a tree. Each vertex of the model is tied to a particular bone, so the model can be controlled with a much smaller number of parameters: the relative positions, orientations, and scales of each bone.

Smooth skinning is a technique used to improve the quality of animations. With smooth skinning, a vertex is not tied to just one bone, but it can be tied to multiple bones (usually a hard limit, such as 4, is set; vertices rarely need more than 3) with corresponding weights. This makes the animator's job harder, since he has to do a lot more work with vertices near joints, but the result is a much smoother animation with less distortion around the joints.

Alternatively, some games use procedural animation, whereby the animation data is constructed at runtime. The bone positions and orientations are computed according to some algorithm, such as inverse kinematics or ragdoll physics. Other options are of course available, but they must be coded by programmers.

Instead of procedurally animating the bones and using forward kinematics to determine the locations of all of the model's vertices, another option is to just procedurally generate the position of each vertex on its own. This allows for more complex animations that aren't bound by bone hierarchies, but of course it's much more complicated and much harder to do well.

Answer 2

Different ways to handle animation in games?

For characters, typically:

1. Skeletal Deformation
2. Blend shapes
3. Sometimes even fully animated meshes (LA. Noire did that)
4. In the recent Tomb Raider we use a compute job to simulate thousands of splines for the hair, and the vertices are controlled by these splines with a vertex shader.

Often these are driven by key-frame animation which are interpolated at runtime, and sometimes we add code to drive the influences (bones, blendshape weights, etc.) procedurally.

For some simple objects that move rigidly, sometimes the design will have animation control over the whole object without having to deform it. Sometimes simple things like shrubs can be made to move by using something akin to blendshapes where you have a full mesh pose in a few extremes and you kind of blend between those extremes.

As for tutorials... well... Are you interested in writing the math for the animation yourself or are you more interested in getting some animated character in your game and focus on the gameplay?

For just doing the gameplay, Unity is a pretty great platform to play around with.

If you are however interested in understanding the math for animation or games in general, here's what I'd read up on as a primer:

• Matrices used for 3d transforms (make sure you understand the commutative, associative and distributive laws, and learn what each row and column represents - they are simpler than they seem)
• Quaternions for rotations (less intuitive, but closely coupled to an axis and rotation)

And don't leave out the basics:

• Vector Dot Product
• Vector Cross Product

Also like 10 years ago I wrote a simple animation library, which is pretty simple, free from most of the more advance concepts so it's not a bad place to look if you want to get a basic idea of how it works: http://animadead.sf.net

Good Luck!