Animation System Overview

Creating animated characters in Unreal Engine 4 involves using several different Animation Tools (or Editors), each of which focus on different aspects of animation.

For instance, the Skeleton Editor is where everything starts as it is used to manage the bone (or joint hierarchy) that drives the Skeletal Mesh and the animation. The Skeletal Mesh Editor is used to modify the Skeletal Mesh that is linked to a Skeleton and is the outward appearance of a character. The Animation Editor allows you to create and modify your animation assets and is where the tuning/tweaking of animation assets are done. The Animation Blueprint Editor can be used to create logic that drives what animations a character uses and when as well as how animations are blended together. Finally, the Physics Asset Editor can be used to create and edit the physics bodies that will be used for your Skeletal Meshes collision.

An Animation Sequence is a single animation asset that can be played on a Skeletal Mesh. These contain keyframes that specify the position, rotation, and scale of a bone at a specific point in time. By playing these keyframes back in sequence, with blending between them, the bones of a Skeletal Mesh can be smoothly animated.

Animation Notifications (AnimNotifies or just Notifies) provide a way for animation programmers to setup events to occur at specific points during an Animation Sequence. Notifies are commonly used to add effects like footstep sounds during a walk or run animation or spawning a particle system during animation. However, they can have any number of different uses, as the system can be extended with custom notification types to cater to the needs of any type of game.

An Animation Blueprint is a specialized Blueprint that controls the animation of a Skeletal Mesh. Graphs are edited inside of the Animation Blueprint Editor, where you can perform animation blending, directly control the bones of a Skeleton, or setup logic that will ultimately define the final animation pose for a Skeletal Mesh to use per frame.

Blend Spaces are special assets which can be sampled in AnimGraphs that allow for blending of animations based on the values of two inputs. Simple blending between two animations based on a single input can be performed using one of the standard Blend nodes available in Animation Blueprints. Blend Spaces provide a means of doing more complex blending between multiple animations based on multiple values (currently limited to two).

The goal of Blend Spaces is to reduce the need for creating individual, hard-coded nodes to perform blending based on specific properties or conditions. By allowing the animator or programmer to specify the inputs, the animations, and how the inputs are used to blend between animations, virtually any type of blending can be performed using the generic Blend Space.

Animation Montages (or, "Montages", for short) enable a wide variety of animation effects, primarily related to exposing animation controls within Blueprint Visual Scripting or through code. They can also be used to create a wide variety of animation effects, including intelligent loops of animation, logic-based animation switching, and much more.

Skeletal Controls (also called SkelControls) enables direct control of bones within a Skeleton asset. These can be used within Animation Blueprints to control an individual bone, create IK chains, and more. This direct control of the underlying Skeleton provides the ability to create procedural, dynamically-driven animation. The Transform of one bone can be used to drive another, or can be used to conform the feet of a character to the ground while playing a walk animation. Any sort of modification can be used to tweak or completely override the bone transforms applied by Animation Sequences.

State Machines provide a graphical way to break the animation of a Skeletal Mesh into a series of States. These states are then governed by Transition Rules that control how to blend from one state to another. As a tool, they greatly simplify the design process for Skeletal Mesh animation, in that you can create a graph that easily controls how your characters can flow between types of animation without having to create a complex Blueprint network.

They also simplify conceptualization of your animation graph. You can start the design of your animation by thinking of the necessary states you will need and how a character may flow from one state to another. A great way to think of them is as a way to break all possible animations for your character into an easy-to-read flow chart, in which you can watch the Skeletal Mesh's state move throughout the chart.

For example, a character may have a state of "Idle" when not moving. Once the character's speed exceeds a certain value, the character may blend into another state of "Movement." There may be any number of other states, such as Falling, Jumping, Crouching, Sprinting, and so forth. By using State Machines, animators and artists can quickly visualize how data is flowing through their animation network.