Non Linear Animation with Blending Tools

An overview of the animation blending tools for non-linear animation.

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Overview

With the new Motion Blending tools, existing animation sequences can be aligned and blended to have characters seamlessly perform a series of animations. The engine automatically calculates offset transformations to align clips and stores that data within the animation sections.

Each animation sequence can overlap an existing animation sequence. The overlapping zone creates a blended region. Traditionally, this blended region would do a simple blending between two animations. This is problematic if you have two animations where the root motion is not located in the same space, then you will see the character transition to the second animation's root location. This is common when blending animations that might have come from different sources. To solve this, you can now blend animations based on a per-bone matching basis. This is particularly useful when blending based on a commonly known point such as when an actor runs, and his foot hits the ground.

Blending Root Motion of Skeletal Animation

You can now blend Skeletal Animation sequences based on their root motion. This means that it is now possible to blend several takes of gameplay animation cycles or keyframe animation to create new animation sequences. This opens new possibilities for using Unreal Engine as a content creation tool for new animations.

Setting Up Skeletal Animation Blending

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To set up a blending of skeletal animations, follow these steps:

  1. Open Sequencer.

  2. Create a new Animation Track.

  3. Add at least two skeletal animations to the animation track.

  4. Trim animation Sequences so that similar poses are at the ends of the sequences to be matched. Push Sequences together to ensure there are no spaces between Sequences.

  5. Right-click on the animation and you will see a new section called Motion Blending Options. Commonly used bones for matching include pelvis, right foot, and left foot.

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    These options include:

    • Match With This Bone In Previous Clip - Matches the selected bone with the previous clips matching the selected bone.

    • Match With This Bone In Next Clip - Matches the selected bone with the previous clips matching the selected bone.

    • Match X and Y Translation - Matches the translation of the root bone in X and Y axes.

    • Match Z Height - Matches the translation of the root bone in the Z axis only.

    • Match Yaw and Roll Rotations - Matches the Yaw and Roll rotation for the root bone.

    • Match Pitch Rotation - Matches the Pitch Rotation on the root bone.

  6. Smoothly blend clips by dragging the skeletal animations so that there is an overlapping region between both animations.

  7. You can now preview the skeleton of the animation on both clips that you are trying to match. Toggle this option on by selecting Show Skeleton. Enabling this shows a colored overlay of the current skeleton. You can manually move the skeleton for better alignment by using the transform tools to adjust it manually.

Along with the visualization of skeletons, you have the option to show a Root Motion Trail. This visualizes the motion and trajectory of the root motion. This can be turned on by right-clicking and under Display and enabling Show Root Motion Trail.

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Blending Non-Root Motion or Static Root Skeletal Animations

The default alignment works by moving the root bone of the skeleton, since gameplay root motion animations usually contain the dominant motion for the root. However, some animations, in particular those acquired by motion capture, may have a fixed root. In this case, you can still match the animation to a bone in the previous clip, but if you try to blend them, it may lead to errors since this is attempting to blend both of the offset roots and the distance between the roots and the first child. In this case, you want to blend the first child of the root, which ignores the root offset between the matched animation sequences and ensures a proper blend. Enable this by right-clicking on the Animation track and selecting Blend First Child of Root.

blended_root.gif

Blending root motion and non-root motion-based animations may not lead to smooth blending.

Control Rig Integration

Sometimes a minor tweak is needed to fix some flaw with the mocap or to change the behavior of an animation slightly to meet the requirements of the shot. Control Rig can be used for such fixes with the Additive Control Rig Solution.

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