MAKING THE LAST BASTION
Ian Dean discovers how Blizzard Animation harnessed Houdini to create the dense foliage for its latest animated short
How Blizzard used Houdini on its latest animation
While the Overwatch game was released to acclaim earlier this year, Blizzard Animation has been steadily releasing short animated films to expand the back-stories of the leading characters. Of the five episodes, The Last Bastion stands out as an incredible technical achievement, and uses Houdini to create a large, dense forest environment and foliage.
The short presented some artistic challenges for the animators. Project director Ben Dai explains that one goal was “to tell the story of Bastion without any dialogue. Another major goal, like all the Overwatch animated shorts, was to expand the game universe by telling great stories about our heroes.”
For VFX supervisor Jeff Chamberlain, it also meant doing things a little differently. “I was hoping we could tell a story that wasn’t typically what you’d expect from Blizzard Animation, but still universally appealing enough to be accepted by our audience.”
Doing things differently meant pushing the FX as much as possible. Houdini has been the Blizzard FX department’s package of choice for the last few years, and FX supervisor David Stephens explains that many of Blizzard’s artists come from a film VFX background, so making more of Houdini seemed a good direction to go in.
“When we were going into this there was a question of whether the plant work would have to be done in Maya, in traditional rigging, or in FX, so getting some of the early results with the hair solver seemed to confirm that we were able to do it,” explains David. “Certainly when we were testing some of the heavier trees, when you get up to hundreds of thousands of branches and
millions of leaves, the fact that we could process that and get it to rig correctly was a good moment for us.”
Moving moss
The animated short includes plenty of standout moments, but it’s the undergrowth, forest foliage and shot of a flowing grassy field that are technically impressive.
“We were pretty fond of the shots where Bastion stands up and emerges from the undergrowth. These were a combination of plant wire simulations riding on top of PBD simulations. They were fun to see come together since so many people and techniques were involved,” says David.
To achieve the detailed feel, the team had to custom model the plants, leaves and trees, using the 3ds Max plug-in growfx, which the modellers then further modified and sculpted in Maya and Zbrush, allowing a fine degree of stylisation. The moss on Bastion was sculpted in Maya and then covered in fibres using Xgen.
“They [the art team] had to custom model a lot of the plants and growth that was around and on top of Bastion, and there was also a layer of some standard library plants as well. So effectively, we had to do a two or three layer thing: we had to take the shell of the moss and that was converted over into a PBD sim in order for that to all kick off as a mass when he’s standing up,” explains David, adding: “As to do the soil sim we had to reattach all of the Xgen moss hairs that had been generated over on the Maya side and reoutput those so that the moss would actually track with it, all in Houdini.”
For the plants, the team would end up merging the two or three different layouts
when you get up To hundreds of Thousands of Branches And Millions of Leaves… THAT WAS A good Moment For us david Stephens, FX supervisor, Blizzard animation
that they had made to create the different plants that lived on top of Bastion. These had been through the process of auto-rigging and had been broken down into their components – details, leaves, flowers and buds.
“eventually, you’d have this great big wire solve that is using the previously done soil simulation as a route anchor for those curves, and then all of that is simulated. Then all of the plants’ hero geometry is deformed based on those curves, and on additional procedural animation based on pivots for the leaves and buds, and [it all] stacks up two or three layers deep for the final result.”
“It’s one of the scariest networks of all time!” exclaims David. “It’s a large system that took months to build. The network is hundreds and hundreds of nodes, and networks within networks.”
Ground work
The development on the soil sims took three weeks. The plant system itself is something Blizzard developed over a period of months, and for The Last Bastion this is more an application of that wider system than something developed for the short.
“essentially, we had a combination of both library plants and then we had custom plants – that was kind of interesting as we just received this giant lump of greenery and we had to kind of go through that and break a few things out so we could convert them into rigs, that’s probably two or three more weeks of custom work setting up the plants,” reveals David.
Another standout moment comes towards the end of the animated short as Bastion
emerges from the forest and walks through a field, a sea of flowing grass. This was done using a Mantra volumetric shader created by senior artist Matt Cordner, to create the distant fields of moving grass, complete with independently moving grass blades.
“The grass is actually in three layers,” says David, with the closest part to the camera being the ‘hero portion’, where the character would walk through and interact with the grass. “Basically, every stalk in there is a wire going through a massive wire solve. So that ultimately ended up being the hero section of the film, and then a second section beyond that uses a Houdini hair system to set up a bunch of curves – some we use as hair renders that actually go back into Maya, but we also use it to drive some rigidly bound instances of some of the plants.”
David continues: “In the hero section, closer to the camera, each of the plants has a wire and fully deforms and bends. The next section out – maybe 50ft beyond that – ends up being a combination of hair and these instances that are being rotated based on a hair and follow the hair. Then, in a third zone beyond that, is a volume shader that was written for Mantra, which produces this lovely cheat from the distance that produces these moving stalks… a volumetric cheat, it’s pretty cool.”
shortcuts
In terms of ‘cheats’, Blizzard overcame the workload of a project like this by considering the shorts as a whole, and also thinking about how they fit into the video game production. The flashback battle scene in which Bastion remembers his war-torn past was one area that especially benefitted from this process.
“At the outset of producing these shorts, we consciously began building up a repertoire of FX techniques that would fit within the game’s art style, so with that battle scene, you’re seeing the amalgamation of many of those FX all in one place. each effect is reasonably stylised, but the scene complexity pushes the overall look back towards something that reads as real,” explains David.
Blizzard’s cinematics team developed a large number of gun-related effects that created with Houdini and Mantra, which came in useful for the battle scene. Over a period of weeks sever artists pieced it together. A HDA - Houdini Digital Asset (also known as OTL) written for The Last Bastion can be used in future cinematics.
“We tend to write a lot of tools for reuse or as starting points for later development, so there’s quite the suite of OTLS [HDAS] now for gun fire effects, lightning, and lately, plants,” explains David. “Because a lot of what we do is custom to the shots, in a lot of cases we have to leave things a little bit looser so that we have room to tear it apart and rebuild it for the next show. When I say we have one OTL [HDA] for a gun effect, we probably have five or six OTLS [HDAS] – from the flash to the sparks to the shells to the tracer fire, it’s a whole suite of tools.” David has been using Houdini for 20 years, so a project of this complexity didn’t phase him, but he does identify what has changed to help newcomers.
“Some of the Shelf buttons and interface advancements that have happened in the last few years help a lot. I think the Wrangle nodes help tremendously because you can get some decent sized programs going there without having to write HDK or do a compiled operator the way you did years ago, and so those things have really helped out and made it more accessible… It’s really very powerful, we wouldn’t change Houdini for anything but calling it easy and accessible does it a disservice.”
The SYSTEM we Created For The LAST BASTION is one of The SCARIEST networks of ALL Time! david Stephens, FX supervisor, Blizzard animation