The nuances of sprite animation

staff_james_vanniekerkI’m Katherine Tymchuk, 3D Artist and Animator for the upcoming mobile game The Horus Heresy: Drop Assault. 

The Basics of Motion

Tacticle MarineWhat personality would a seasoned Terminator have? Is he proud warrior with his shoulders up, or a primal beast, hunched over his lightning claws in anticipation of battle? How would the Heavy Support Squad run under the weight of his rocket launcher? How can we convey the Conversion Beamer tearing through all of time and space? These were some of the questions we asked ourselves when starting to work on the animations for The Horus Heresy: Drop Assault. We’re very luck in that there is a ton of great visual reference from the Warhammer 40,000 universe. However, there isn’t a lot of reference for these things in motion, which led to some unique challenges in creating our own animations for each troop type in Drop Assault.

Believe it or not one of the animator’s best tools is their body. We act everything out. Seriously! I wish I had videos of us running and jumping around our office pretending to be the Titan landing on a base or the Dreadnought scorching enemies with its Flamers. Acting and moving helps us understand how we want characters to move. Seeing that motion in action provides the best reference. We also spent time interacting with the various sculpts from Games Workshop to get a feel for how everything from vehicles to weapons to characters function. With our concepts and ideas firmly in place, we built animation “rigs”, a skeletal structure similar to puppetry used to bring our characters to life, and went to town.

The Devil is in the Details

Tacticle MarineSeveral challenges were introduced when we decided to use sprites instead of full 3D models for the troops and buildings in Drop Assault. Using sprites allowed for greater detail on our troops to be closer to the original Games Workshop models, while using less memory so our game could run on older devices such as the iPad Mini and the iPhone 4, however it meant extremely tight management of frame count and texture space.

This meant that we had to change our established animation workflow. Normally animations are done at 30 to 60 frames per second for use in game and animations are generally anywhere between 2-10 seconds in length. Most animations in Drop Assault have 6-10 frames in total. When rendering our characters in sprite form we had a very limited number of frames to work with. Every frame had to count. With each one we would need the character to strike just the right pose or to achieve a readable silhouette. Every animation was reviewed countless times to ensure that each frame added to the animation, and that the motion was smooth and fluid. Once animations were approved, we rendered all of our troops in a single lighting scene to add consistent light, shadow and special effects. That was the easy part.
We then packed each troop’s series of frames onto sprite sheets. Using these sheets, we re-created the animations in Unity. We used Unity’s Mecanim animation system to create animation trees for easy transitions and blending, but we also ran into further challenges.

That’s a Lot of Animation

Tacticle MarineEach troop had three or four animations (idle, walk, attack, etc.) and were rendered in 8 or 16 directions depending on how they looked when rotating (big tanks, for example, needed more directions to rotate smoothly). Each unit also has four different legions. For the Tactical Space Marine alone, that adds up to a total of 256 animations. To avoid setting up each animation manually in Unity, our tech team wrote tools for swapping frames on the fly. We also had to be smart with our sheet space. Tricks such as not rendering out the full Fire Raptor gunship five times when only the thrusters are animated were used wherever possible, to be efficient without sacrificing animation quality.

As a fellow Warhammer 40,000 player (go go Dark Eldar), it was an honour to work on the animations for Drop Assault. Seeing your army and the team’s hard work come to life has been the most satisfying part of this project, and now it’s hard to go back to the tabletop game without imagining my troops running around the battlefield slicing, shooting and blasting their way to victory!

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