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Hitstop Animation System
August 2023 - January 2024

The Hitstop Animation System is a project to create an attack impact based animation VFX system in Unreal Engine 4. It draws inspiration from traditional 2D beat-em-up and fighting games.

Leonardo and Donatello TMNT rigs courtesy of Agora.community

Highlights:

• Animated in Maya

• Implemented Animation VFX system with shared rig & blueprints for both characters
• Consists of two character mesh effects
  • Mesh offset (or Hitshake)
  • Animation pause or slow (Hitstop or Hitslow)
    

• Designer parameter control independent of blueprint scripts

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Mesh Offset (Hitshake)

When a hit occurs, the character mesh if offset on an oscillating system. The mesh is offset horizontally, held in offset position for a set duration, then reset to original mesh location. This repeats with a diminished offset for however remaining loops of the effect there are.

If the system were to be extended for vertical movement and jumping attacks, the mesh would also be offset in the vertical axis to preserve vertical momentum.

Hitshake system

Animation Pause & Slow (Hitstop & Hitslow)

Character animation is modified with a pause or slow depending if the animation is a defending or attacking animation respectively (denoted as Hitstop and Hitslow). The intent is to keep a consistent flow of motion for attackers, while defenders have a hard pause of momentum in interactions.

Hitstop & Hitslow work on a simple timer system of applying their animation modification, waiting for a set time, then resuming the normal animation play rate.

Hitstop & Hitslow timer systems

Hitstop

Hitslow

A key difference from the Hitshake system is applying the VFX when the animation is at marked keyframes that look best when held for multiple frames. Using animation notifiers in UE4, each animation marks their start frames when the animation pause/slow should wait.

This also allows an animator to modify the timing of their animation or which keyframe to hold on without directly affecting blueprint code.

Attack animations wait until impact keyframe for Hitslow

Defender animations wait until reaction keyframe for Hitstop

System Control

Design of the system focused on exposing control of the system in a way that would allow a designer to tune the feel and look without directly editing the blueprint code. Using Data Assets, hit VFX parameters are defined outside blueprints in their own directory within the project.

Data assets for the Hit Animation system consist of:

• Hitshake amplitude (how far the mesh offsets from origin position)
• Loops of effect
• Duration of hitstop/slow effect
• (For attack animations) Hitslow play rate change
  

DA_AttackVFX_Level1 controls animation system intensity for the 'basic' punch