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Xbox 360 Programming Considerations

Summarizes several issues that XNA Framework programmers should consider when creating Xbox 360 games.

Graphics Considerations

The most important graphics consideration for programming for the Xbox 360 console is the wide variety of televisions that the Xbox 360 system supports. The Xbox 360 system supports both HDTV and normal television sets, at multiple resolutions (480p, 720p, 1080i, and 1080p), and multiple aspect ratios (4:3, 16:9, and 16:10). The console automatically scales the output of a game to the resolution of the owner's display, and if the game is using a widescreen aspect ratio, the console automatically adds "black bars" (letterboxing) if the owner's display is not widescreen.

There are still two things, however, XNA Framework programmers should consider when programming for the Xbox 360: the title safe region, and aspect ratios.

Title Safe Region

On standard tube televisions, the display area of the television normally is not a perfect rectangle. In fact, a significant amount of the display may not be visible on a CRT tube. In television, the inner 80 percent to 90 percent of the picture is considered the "title safe" region. Any graphics displayed outside of this region on a standard television may be obscured or distorted.

Programmers should ensure that any critical information (score, number of lives, ammo, and so on) is displayed within the title safe region while drawing the background or a 3D scene across the entire display. Critical text should be displayed within the inner 80 percent of the screen. Programmers should also ensure that any text displayed on the screen is large enough to be legible on a standard television.

Aspect Ratio

If the aspect ratio of the back buffer is widescreen and the aspect ratio of the owner's display is not, the Xbox 360 will add black bars at the top of the display so that the entire back buffer is on the screen. To avoid letterboxing, developers must program their games to use both standard and widescreen aspect ratios, and adjust their display to the default aspect ratio offered by the Xbox 360. For this reason, a single widescreen back buffer for Xbox games is recommended.

To detect the console display setting, you can use the DisplayMode property on the GraphicsDevice. This will be valid during or after your game's Initialize method. Some common display modes are listed here.

Xbox display settingDisplayMode width and height
AV (composite)640×480
480p (normal)640×480
480p (widescreen)640×480
720p (widescreen)1280×720
1080i/1080p (widescreen)1920×1080

Multisampling

Because 4×AA multisampling is provided for free by the Xbox 360, it is recommended. Developers should be aware that this will often activate predicated tiling.

Multiple Render Targets

Render targets function similarly on both Xbox 360 and Windows. By default, the content of a render target is always cleared when the render target is resolved unless persistence is specified during construction of the render target. Developers can avoid problems by rendering fully to each render target before using a new render target, and by rendering their final scene after all the other render targets are resolved.

Input Considerations

The Xbox 360 supports three input devices: the game controller, the Xbox LIVE Vision camera, and an optional USB keyboard. Mice are not supported, and most Xbox 360 users will not have a keyboard connected to their console. The XNA Framework does not support the Vision camera. Games for the Xbox 360 should be programmed to accept all critical input from the gamepad.

Audio Considerations

XACT audio wave banks, sound banks, and settings files are platform-specific. The XNA Framework Content Pipeline will automatically process XACT project files (.xap) into the correct platform type if the project file is added to Solution Explorer. If you are building the XACT project manually, ensure you are using the correct built files for your platform type when you load the built files into your game. Failure to use the correct platform-specific files will result in an error.

Storage Considerations

Accessing a player's storage on Xbox 360 (to let them save a game, for example) requires displaying the Storage Device Guide where the user can choose between the hard drive or memory units. The best way to do this is to use the BeginShowSelector method as demonstrated in Getting a StorageDevice Asynchronously. The largest space available on a memory unit is 52 MB so any saved games must not exceed that size.

The maximum size of an XNA Framework project on an Xbox 360 console is 2 GB so the entire game, including support files (level data, sound, and so on), must not exceed that size.

Source Code Considerations

Xbox 360 projects define an XBOX symbol for use with conditional compilation directives such as #if. You can use this to maintain source code that acts differently on Windows and Xbox 360 if that source is shared between projects.

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