Aug 28

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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staff_cory_chatwellI’m Cory Chatwell, 3D Team Lead on Horus Heresy: Drop Assault. As team lead my job is to listen to every department on the project. I sit down with designers, programmers and artists and gather all the goals and restrictions from the team and then try to find ways to satisfy all of these requirements while maintaining a balance between visual fidelity and performance.

Target Goals

The bulk of my input on a project is in the early planning stages. I wanted to share with our fans how we’ve gone about doing environment planning and map design.

The environments in The Horus Heresy: Drop Assault had to have depth. Going for a 3D approach with the environments (versus 2D like the unit sprites) allowed us to create a parallax effect and give players the feeling that they’re really interacting with the world.

We needed…

  • A building system to accommodate any number of map layouts
  • A variety of geographical regions to be represented
  • To capture the look and feel of a post-apocalyptic, recently virus-bombed Istvaan III
  • It to feel as intricate and detailed as the rest of the Warhammer Universe
  • And it had to look and run great on relatively low power devices like the iPhone 4.

It was clear early on that we would need a systematic approach for the majority of maps, a system that still held up visually and allowed the flexibility needed for designers to create their vision.



Each map consists of two regions: the playable area in the centre that needed to remain relatively flat and clear of obstacles to allow for the custom placement of defenses and troops, and the surrounding environment frame. The playable area was a challenge in that we needed the ability to make as many playable area layouts as the designers could dream up. We ended up creating a series of sixteen tile shapes as well as a map layout tool that would allow the map designer to place, rotate, flip and align tiles and defensive structures however they saw fit. Along the way designers would sometimes request unique pieces or additional elements to further flesh out the maps. Using a tile system meant it was simple to incorporate new elements along the way. Creating a quick and easy system for map design was a real focus in the early stages of development. Developing the tools and the process early on was key to producing the amount of content that we have.

The next step was the creation of the environment frames. While the playable areas were built systematically using tiles, the frames were all completely custom. We based the look of Istvaan III off established lore and conceptual art, drawing influence from the Horus Heresy books and the available kits from Games Workshop. These frames contain the rich details that flesh out the world: mountains, rivers, cathedrals, towering bridges, statues and more. The goal here was to match the already established architecture and visual design of the Warhammer universe and make the maps feel grounded in the world of Istvaan III. Fans of Warhammer will no doubt recognize the iconic gothic spires and steel plated fortifications from the “Wall of Martyrs” or “Fortress of Redemption” kits, and many others were directly referenced.  After recreating many of these elements in 3D, we had a lot of fun kit bashing and destroying them to create environments that we found would best represent the virus bombed surface of Istvaan III.  The player’s base is nestled in the remains of a shelled keep atop a cliff. This gives the player a sense of safety in their own fortress, while still conveying the apocalypse that has ravaged the old ruin. When the player ventures outside these walls they are met with fierce battles across the desert remains of urban centers, as well as more rural industrial areas, mining complexes and mountain ranges.

Another challenge that we faced was the technical restrictions on map size. In order for units to know where they could and could not walk and how to get where they were going, the map creation tool had to generate a “navigation mesh” based on the tile layout. These navigation maps could only be so large before they started to bog down performance on devices. Sometimes limitations can actually be helpful. In this case it allowed us to create environment frames that fit all sizes of map by modeling them at our maximum navigation mesh size. We created the foreground and background as separate sliding interlocking pieces, from there all we had to do was drop in the playable area and adjust the frame to match.

Working on the battle environments for Drop Assault has been a really fun and exciting challenge for us. We can’t wait to show you what else we have in store for the Horus Heresy: Drop Assault, so stay tuned for updates.