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Animation is the science and art of creating the illusion of motion. From antique kinetiscopes to cutting edge digital effects, this is done by exploiting the sensory phenomenon called persistence of vision, which causes a series of individual pictures to be perceived as a single, continuous image if displayed one after the other at a fast enough rate. By changing the content of the pictures, the illusion of smooth motion can be created.

In the Unreal universe, animation is the principal deity – nearly every aspect of the game engine and its thousands of "moving" parts (pun intended) contributes to achieving the ultimate goal of delivering a series of constantly changing images to a computer display. When all goes well, we willingly suspend our disbelief and enter that universe to play the game. If things get glitchy (framerate drop, netplay lag, etc.), the illusion can be broken.

"Animation" need not refer only to apparent motion – any visually detectable change over time in a series of images (such as changes in color or texture) is also animation. That is the heart of the art – change over time.

For Unreal game content developers, "animation" can be more narrowly defined. There are five types of animation techniques directly accessible for content creation: texture animation, mover animation, cinematic animation, vertex animation, and skeletal animation.

Texture animation
The creation of any change over time in the textures applied to the surfaces of objects in Unreal scenes. TexPanners, TexRotators, and MaterialSequences are examples.
Mover animation
Uses game engine programming to create positional changes over time of 3D objects in the Unreal scene. Mover animation is implemented by designating a 3D object in a map as a Mover, and specifying a sequence of positional changes (keys) and the time to move between each.
Cinematic animation
Related to mover animation, but employs defined motion paths for objects, including the depicted viewpoint, if desirable. The Matinee tool is used to create cinematic animation – InterpolationPoints are placed in a map to describe the motion path, and the SceneManager's Affect and/or AffectedActor properties are set to specify the object being moved. Actions and SubActions properties further define the motion characteristics.
Vertex animation

A method of creating motion in a 3D model mesh by directly manipulating the individual vertices of the mesh. This was the principal 3d mesh animation technique used in Unreal 1, and is still employed selectively in UT2003 for such objects as the waving-in-the-wind CTF flags and the bio-rifle goop blobs. Vertex animation of characters and some types of weapons is a laborious task, and has been largely superceded by the skeletal animation technique.

Vertex animation requires a modeling/animation program ( e.g., 3DS Max, Maya, or MilkShape) and the use of a utility (e.g., ActorX, 3ds2unr) for exporting the animated meshes to a form that can be imported into UEd. Currently vertex animation requires some Unreal Scripting to fully implement.

Skeletal animation

A technique for animating 3D meshes by using a controlling understructure, commonly called a skeleton, that is invisible in the game. The skeleton can be constructed to mimic the proportions and range of motion of a human skeleton, making it an ideal technique for animating humanoid characters, but it can be applied to many other animation needs as well. One of the strongest features of skeletal animation is that it can employ inverse kinematics, which greatly simplifies the creation of certain types of animated motion.

Skeletal animation requires a modeling/animation program ( e.g., 3DS Max, Maya) that supports the technique, and the use of a utility (e.g., ActorX, unEditor.mll) for exporting the skeletal animations to a form that can be imported into UEd.

Both gmax and Maya PLE, the freeware versions of Max and Maya that Discreet and Alias provide for non-commercial use, can be employed to produce 3D mesh animations, but their limitations can complicate the process of getting the result into UT2003.

The choice by a modeler/animator of which animation technique to use for a particular task depends on the nature of the motion to be simulated. The surface appearance of an object can be animated using the various moving texture types. For motion through virtual 3D space, when the form of a moving object does not change, mover animation is usually adequate. More complex motion paths, and "camera" motion, can be accomplished with cinematic animation. Motions requiring a 3D object to change its shape in a complex fashion (such as the multiple waveforms present in a breeze-blown banner) are best portrayed with vertex animation. Skeletal animation is most useful where sections of a mesh object move as separate units (such as an arm or leg), and the units can be "attached" to a skeletal understructure.


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