The Camera Systems of God of War III!

God of War III is a hit title released by Santa Monica Studios and Sony Computer Entertainment.  As the third title in the God of War series, GOW III was released back in 2010 for the PlayStation 3.  As a third person action adventure game, GOW III falls into a category that is filled with great titles from various AAA developers.  Because of this reason, the developers of the GOW series needed to differentiate themselves in a way that had not been seen in the current market by players.  The main way the developers chose to do this was through the cinematic feel they imbued in the franchise, via their in game camera systems.  Since I have already covered the basics of camera systems in games in my previous blog post, this post will focus more on how GOW III designed, tweaked and implemented into their game to create these breathtaking cinematic experiences that have helped to cement this series as one of the greatest third person action titles of all time.

At the beginning of the development of the GOW III camera system, Sony Santa Monica realized that one of the main reasons their games have been so successful, is because of the camera systems that they have implemented in their two previous titles.  For this reason, SSM wanted their third title to have the most epic feelings possible for the player experience.  To accomplish this task, four of the 120 team members working on the title were given the sole tasks of creating and implementing this intricate scripted camera system for GOW III.  The teams theory behind having a completely scripted camera system tied in with their already outstanding gameplay mechanics that had been working for the past many years.  They felt that if the gameplay in a game is solid and fluid, why should the camera be focused solely on the characters close vicinity, when it could pan across a beautiful scene while the player hacks and slashes their enemies.

This scripted camera system is unlike most traditional third person games where the player is given control of camera movement, since in GOW III the player has no influence on camera position.  For this process to be successful in game however, there must be a significant amount of time put into each cameras exact position.  For the GOW III team, this whole process started out with simple level design sheets being provided to the camera team.  With these design sheets in hand, the team is able to figure out the best locations for camera placement based on enemy locations, where the player needs to be moving towards, and unlockables that need to be visible for the player.  Once all the cameras have been implemented and playtested, the camera team sends their work to the art department.  This is where the majority of the level and camera design time is spent, as the artists are required to create these massive and epic scenes around the camera design of the level.  Before the completion of a level, the art department will send the level back to the camera team, as many cameras will need micro adjustments to work within the level being designed.  This is a very tedious process for the team, but it is necessary to accomplish that cinematic feel that everyone looks for in a GOW title.

What the camera team sees while designing a level!

Now, since a scene can have anywhere form a few, to dozens of camera locations, the design team needed a way to keep everything within the frame, while simultaneously showing the landscapes and epic designs that the artists had spent so long working on.  The first system that I discovered while learning about the GOW III camera system was the rail/dolly system they used.  This system was mainly introduced in the GOW III as the technology had advanced enough to allow for this.  Usually this system was used in long linear sections of the game.  How this system works, is that the designers would set a NURBS curve along the path they want the character to take.  A camera is attached to this curve, as well as many points that the camera can smoothly interpolate towards.  The animations are mapped to the rail as well, and during each frame, the system calculates the nearest point on the rail in relation to the character model, and interpolate the camera to that point, making for a movie style dolly effect.  Now this works great for following the character, however the designers needed to implement what they called the boom of the camera as well.  This boom was used for calculating the look vector of the camera, starting at the dolly and ending at the target position (generally the character model).  This boom would allow for panning in and out of the scene, as well as up down movement of the camera to allow for showcasing of the beautiful environments of the game, while still keeping the player in the viewport.  

The Rail Driven system used in GOW III

 

Now the system shown above works great in many of the level traversal aspects of the game that are critical to the gameplay.  However, the team needed to design a system that would work for when the main character Kratos is fighting multiple enemies in a large, wide open setting.  For the camera system to work well, Kratos needs to always be in frame and the focal point, but the team also needed to keep all enemies visible for the player as well.  To deal with this dilemma, the team implemented a weighted average camera system.  How this functions is that each character is given a weighting of "importance" in the current scene.  Generally Kratos is the highest weighted the team wanted to keep him as the central atom of the camera.  These weighted positions are all added together and then divided by the sum of all the actual weightings of each character.  This gives the team a value that they can then feed to the boom system to use as the boom target, effectively keeping every character within the viewport of the scene.  An important note is how the team gets these weights for each character (ranging from 0 - 1).  We already mentioned the base weight of the character (how important the character is), but the team also takes into account the distance weight (distance from the hero, not the camera), as well as the activation weight of each character.  This activation weight is used to smoothly transition the camera when an NPC is spawned into the scene (a high weight) or when they are killed off (a low weight).  This value helped to remove the jerking around that occured with the camera when an enemy was killed and the cameras boom target value would change drastically from one from to the other.

This system worked great when the team was testing large battles with a plethora of enemies, but when testing one on one fights, they stumbled across an issue with the weighted average system.   

As seen in the image above, the camera is too far away from the action then the designers had originally planned.  So they decided that instead of implementing the weighted average system throughout the entirety of the fight scenes in the game, they would also implement a new system which they called prioritized framing.  Along with the weighted average system, the prioritized framing system is used in the majority of the large scale battle sequences in GOW III, so I felt it was important to cover the basics of this system as well.

The main focus of this new system, was to ensure that the highest priority entity (in this case Krators) is always remaining in the frame of the scene.  From here the system would work outwards by priority level, doing its best to include as many of the less important entities as possible, while still keeping an acceptable frame distance.  The system worked on an algorithm that functioned as followed five steps to function, the first being centering the camera on the heroes location.  From here, the algorithm calculates the extents of  the lowest of the priority levels.  Now that we have these extents, we can minimally track to frame extents of the current priority level we are focusing on.  Step for is variable in time to complete, as the algorithm must work its way through each priority level completing steps two and three of the process. Once all the priority levels have been completed however, we can calculate the delta to the Azimuth and the elevation that will be needed for the booms target location.  For a visual representation, the framing would begin as this: 

And end up as this, where the red is the out of frame area with NPC's still inhabiting the space:

It was a truly ingenious fix to the problem the team was having, as they came to the realization that not all of the enemies are relatively important enough to be on screen at all times.  Also, if we remember the zoomed out screenshot shown above, the fix implemented by the team showed through as the scene now looked like this: 

Zoomed in more and framed correctly!

The cameras implemented in God of War III are truly works of art that shine through in the gameplay.  Creating these epic cinematic sequences is no small feat by a team, and the work is definitely evident when a player takes control of Kratos.  Not only does that camera work as a viewing mechanism in the game, but it also becomes the players ally at times, giving hints on different unlockables, as well as panning slightly to reveal where the player must go next.  Its a truly remarkable system that I would personally love to see carried into more games in the future.  Hopefully the God of War team can bring this technology to a next-generation game and further prove to us how versatile and amazing a camera system can make a game! 

God of War IV would be pretty nice!