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10 Tips: Getting the Most from Motion and Performance Capture

July 4, 2012 Article Start Page 1 of 3 Next
 

[In the second of Gamasutra's discipline-specific series gathering important tips and techniques direct from developers, Tristan Donovan delves into motion and performance capture. You can read his prior article on audio, here.]

Motion capture technology has come a long way in the past decade. Cameras are cheaper, the software is better, and even the challenges of tracking eye movements are being overcome. At the same time, motion capture has also become more commonplace in games -- so much so that it's more common to see motion capture than hand animation in most big-name console titles.

That's all well and good, but what makes the difference between a successful motion capture shoot and a mountain of useless data? What techniques allow you to get the most out of your actors -- and are there times you shouldn't even use trained actors at all?

In this feature we ask the motion capture pros behind games such as Halo: Reach, Fable III, Total War: Shogun 2 and Sniper Elite V2 for their nuggets of mo-cap wisdom.

1. Prepare, prepare, prepare

If there's one single piece of advice that everyone involved in performance capture agrees on it's that preparation is everything. "Of all the advice I have for successful motion and performance capture, this is the most important," says Kurt Nellis, the technical cinematic lead at Bungie.

"Before you set foot in the room with your talent suited up and the crew looking at you expectantly, know what you are shooting. It saves a tremendous amount of time, as you won't be caught with your pants down because you don't know the answers to the questions everyone will undoubtedly have on set."


Bungie's Halo: Reach

Pete Clapperton, motion capture manager at Creative Assembly, the studio behind the Total War games, adds that it's good to set out the rules of communication in advance, too. "During the shoot there's normally a lot of people, and it's always a good idea to make sure everybody knows exactly what role they are playing on the day, because you don't want three people giving directions. The main roles are the person working the system, the person watching for any markers that fall off, and the director -- there are other people, but they need to know when to shut up."

2. Save time with animation

When making Sniper Elite V2, Rebellion Developments waited until the game reached first pass standard before turning to motion capture. "This allowed us to fully explore the style of the animations and react quickly to the evolving design and code requirements as the project progressed," says lead animator Zsolt Avery-Tierney. This meant time and money wasn't wasted on collecting redundant or incompatible motion capture data and that the team entered the shoot with a clear idea of what they wanted.

"Everything in Sniper Elite V2 that we gained from our actors was initially defined and designed by our animators. This not only served better communication on the day but also ensured our animators retained ownership and remained devoted to the final delivery," he explains.

Another benefit was that because the content was already well defined, Rebellion could tell its mo-cap studio its exact prop requirements and measurements in advance: "This maximized time usage on the day, drastically reduced asset waste, and relieved the third pass burden on the animation team."


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Comments


TC Weidner
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Is there a library or collection developers could just tap and license? and if not, why not. I mean how many basic range of motions are there? How many ways are there to crouch and fire, jump? etc. It would seem to me like there is a lot of reinventing the wheel here. I'm ignorant in this area, so Im just asking.

Matías Goldberg
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Hi, there are a few free libraries out there, but they're far from perfect.

But regardless, the main problem is that each engine has it's own needs. Not all rigs have the same bone layout. Although for humans it's often more or less the same, they're different. Animation retargeting aims at solving that issue, but it still require a lot of user intervention.

Furthermore, some engines blend full animations together to create a composited animation, while others only blend a few bones independently, not all of them.

Some games require a run animation to be stationary, while other games require the animation to translate all of it's bones accordingly to the motion of the subject (games implementing motion extraction to prevent "sliding foot" and cause more realistic movement often require this)

In other words, the animation has a lot of technical requirements specific to the engine it is going to be used with. That's why Sniper Elite V2 waited so long. If your engine changes how it handles the animation, all your animation data (mocap and non-mocap) may suddenly become useless.

And jump? There's Assassin's Creed style jump (jump forward, low altitude, can't change direction), Mario jump (high altitude, non-realistic, instantaneous, can change direction), God of War jump (simple animation, but allows blending for attacking mid-air), Zelda jump (jumps only on spot when still or at edges while running). Which one do you need? They're all 4 very different styles of jumping, each adjusting to the gameplay needs.

While it looks like reinventing the wheel, it's more like creating a specific wheel tire for a weather condition that never repeats.

One could adapt the engine to a specific animation library (considering the mocap performs always use the same conventions and stay consistent in all of their animations) but you'll be limited in terms of gameplay & tech. This constraints creativity to Indie developers (their strong point) while big budget titles will prefer paying for a custom mocap (for many reasons). The void in between that can be filled with a licensable library may not be thaaat profitable.

TC Weidner
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@Matias

thanks Matias, that was very informative

Jimmy Corvan
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TC some places do keep a library of moves and license those moves out.

However, most major developers have more specific needs than a library will offer. For starters each game will have it's own frame count requirements making timing important. Additionally, your basic movements will vary, drastically, based on the characteristics of the character. That is, Master Chief needs to walk differently than, say, the Hero character of Fables.

TC Weidner
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ah, ok, thanks


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