Administrivia

1
Administrivia

• Any questions?
• Homework 1 (second hw)

2
XNA (XNA Not Acronymed ?)

• Derive from Game class
• Must override
• Initialize setup (one time)
• Update compute game logic
• Draw display
• Separation of logic and display is an important
  model
• Not just for games, but in general this is a good
  idea
• Game.Run starts the game loop

3
Fixed-Step Game Loop
Initialize

• Set Game.IsFixedTimeStep to true (default)
• TargetElapsedTime default 1/60th of a sec
• Slow IsRunningSlowly (bool)

Update
Times up
Set Slow
Not Time Yet
Draw
Times up
Not Time Yet
Wait
4
Variable-Step Game Loop

• Set Game.IsFixedTimeStep to false
• TargetElapsedTime ignored
• ElapsedGameTime time since last call to Update
• This works in either model

Initialize
Update
Draw
5
Contrast The Two Models

• What if user has lots of other tasks running?
• What if you use two different computers?
• If you have a sprite moving across the screen,
  how will it behave?
• Note debugger entrance causes timer to be
  suspended

6
GameComponent

• Game provides a collection of GameComponent
  objects or DrawableGameComponent objects
• Mechanism to modularize your solution
• Good if you want to create components that are
  reusable
• Game.Components.Add

7
GameServices

• Allows interface to services
• Look up by finding a service that implements an
  interface
• Dont have to use explicit object reference
• Good for modularity and reusability
• Services.AddService( typeof( IMyService ),
  myobject )
• IMyService myservice (IMyService)Services.GetSer
  vice( typeof(IMyService) )
• Graphics services, networking services, etc.

8
Game Content

• Problem how do you make it easy for content
  authors and programmers to work together?
• Artists create content using many different
  Digital Content Creation (DCC) tools
• Problem how do you deal with Windows and Xbox
  360 assets?
• Solution XNA Content Pipeline

9
Content Pipeline Architecture

• XNA provides content importers and processors
  that will load and process the content for your
  game
• Creates Managed Object with Strong Typing
• Content manager (Content.Load)

10
Standard Importers

• Autodesk FBX format
• Directx Effects File format
• Sprite Font file
• Texture importer (.bmp, .dds, .dib, .hdr, .jpg,
  .pfm, .png, .ppm, and .tga)
• DirectX X file format (coordinates)
• XACT for sounds
• XML Content
• Note 3rd party importers available or you can
  write your own

11
Understanding the Displays
12
Back Buffer

• Title safe area is inner 80 of the back buffer

13
2D Graphics

• Drawing sprites
• Sprite origin normally upper left corner, but you
  can change that
• Sprite depth (floating point number) between 0
  (front) and 1 (back)
• Use sourceRectangle if you want to draw part of a
  texture
• You can also scale the texture in the Draw
  command (uniform or non-uniform)
• SpriteBatch lets you do a transformation matrix
  (rotation, translation, scaling)

14
3D Graphics

• Triangles, triangles, triangles lots of them
• 3 vertices
• Vertex X,Y,Z coordinates, color, normal, etc.
• World Coordinate space (position of vertices)
• Position camera to view triangles

Map to 2D
15
3D Graphics - 2

• Shader and effects
• Allow display of vertices (and pixels) using a
  program written in HLSL (High Level Shader
  language)
• Transparent, semi-transparent, use particular
  colors, etc.
• In XNA always have to use an shader/effect
• Matrix transformations to vertices
• Translation
• Rotation
• Scale
• Apply texture to a triangle
• Specify lighting location
• Vertex and Index buffers to stream lots of points
  to the graphics device for rendering

16
Multiplayer

• See Tutorial 5 Adding Multiplayer and
  Networking Support to the Game
• Support for
• Gamer sign in
• Gamer creating or joining a session
• Lobby waiting for players
• Reading and writing network packets of the game
  state
• Think about Two-Player, Networked Game
• Issue is what do you send back and forth
• Reduce network traffic and lag time by reducing
  what you send