Lecture Building a 3D-game using XNA 1Elias Holmlid

 First part  General thoughts on game engine architecture, and some XNA considerations  Second part  Adding a skybox and mouse-look to our previous code Elias Holmlid2

 Engine (library)  Shared package (library)  The actual game  Editor  Playpen (sandbox)  Content pipeline- extensions Elias Holmlid3

 Break down code into smaller components  RenderingComponent  PhysicsComponent ▪ Collision ▪ Response  SoundComponent  Components should not be aware of eachother  You might use the already existing GameComponent-class Elias Holmlid4

 When working in teams, naturally breaks down responsibilities  Easier to replace code  Alot easier to nail down bugs and performance problems Elias Holmlid5

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 Since components are not aware of eachother, they have to use an indirect way to communicate  This can be accomplished using events Elias Holmlid7

 EventManager  Basically contains a dictionary from event type to a list of listeners for each event  When an event is sent, all the listeners are notified Elias Holmlid8

 Examples  PlayerDiedEvent  GameAboutToPauseEvent  LevelCompletedEvent Elias Holmlid9

 Break it down into separable parts: Elias Holmlid10

 Find a good way to quickly add new effects  For example, decide upon common variable / semantic names for different common  The application can then set the parameters automatically for you Elias Holmlid11

 SceneManager  CameraManager  LightManager  EffectManager Elias Holmlid12

 A tree containing the entire scene  Objects can be placed and rotated relatively to eachother  Easy to group objects Elias Holmlid13

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 Example1: EnemyObject  Contains common stuff like position, model etc  Enemies might have different behaviors: ChaseBehavior, JumpAroundBehavior...  Example2: Camera  Camera does not control itself, instead a CameraController-class is moving the camera Elias Holmlid16

 Use a fixed time-step or multiply all your movement calculations with the time passed since the last frame  Game.IsFixedTimeStep = true/false  No ”best” approach: Shawn Hargreaves has a good (as always) article about this: 7/07/25/understanding-gametime.aspx Elias Holmlid17

 Flips the back-buffer when the electron beam travels to the top-left of the screen (a state called vertical retrace)  SynchronizeWithVerticalRetrace property of GraphicsDeviceManager Elias Holmlid18

 The most important rule:  Never allocate reference type objects (classes) while the game is being played  Value types are ok (structs, primitive types...)  The garbage collector is a much bigger problem on the Xbox360 Elias Holmlid19

 Garbage collection  Memory allocated on the heap exceeds a given limit: ▪ GC kicks in to release unused memory  Unacceptable 1: GC triggers too often  Unacceptable 2: GC triggers infrequently but it takes a looong time for it to complete  Read more here: /07/02/twin-paths-to-garbage-collector- nirvana.aspx /07/02/twin-paths-to-garbage-collector- nirvana.aspx Elias Holmlid20

 Use pooling  For particle systems, enemies etc  Should use this in non-garbage collected environments anyway Elias Holmlid21

 So, allocate everything while the game is loading  You might also force garbage collection through System.GC.Collect() which will reset memory count to zero ▪ Do not do this while playing the game though! Elias Holmlid22

 CPU or GPU bound? Elias Holmlid23

 How can you tell if you are GPU/CPU bound?  Some detective work is needed  Example: run the game at a tiny resolution. Does the framerate improve?  In that case, you are bound by the pixel shader stage ▪ Try doing cheaper pixel calculations ▪ Or if you are happy with the framerate, you can do more heavy vertex processing for free Elias Holmlid24

 Two blog-posts I recommend:  03/31/an-elf-in-a-box.aspx 03/31/an-elf-in-a-box.aspx  04/11/santa-s-production-line.aspx 04/11/santa-s-production-line.aspx  (Read them in that order)  Elias Holmlid25

 Subscribe to Shawn Hargreaves blog:   Hang around at the Creators Club Forum:   People there are really friendly, and if you’re lucky, Shawn himself will answer your questions Elias Holmlid26

 A cheap way to simulate scenery far far away  Imagine walking around in the center of a textured sphere, where the sphere is always moving along with you Elias Holmlid27

 We can use a cubemap for the sky-texture Elias Holmlid28

Elias Holmlid29  Use the local position of the vertex as a direction vector for lookup into the cube texture

 Turn off backside culling for sphere or change cullmode (we’ll be inside the sphere)  Always pass depth test and write maximum depth (1.0) for each pixel to depth-buffer  Nothing in the scene should be farther away than the sky Elias Holmlid30

 Cubemaps constructed with special tools  CubeMapGen is a free tool from AMD: pages/default.aspx pages/default.aspx Elias Holmlid31