DirectX and Windows XP

This topic contains tips for using Microsoft?DirectX?on Microsoft Windows?XP.

Handling Multiple Users
Fast User Switching
File Storage
Registry Storage

Handling Multiple Users

Windows XP allows multiple users to be logged on to one computer at the same time. If your application cannot run multiple instances simultaneously, you should check to see if another instance is running before starting a new instance. You cannot use FindWindow across desktop sessions. FindWindow only works within the current session.

To see if an instance of the application is already running, use a global mutex. If an instance is running, you can use FindWindow to see if the instance is in the current session and restore the window. Otherwise, notify users that they cannot use the application.

Fast User Switching

Fast User Switching allows users to switch between sessions. Users do not have to terminate their applications or log out for another user to start a session. Instead, they use Fast User Switching, which enables another user to log on and work on the computer.

DirectX applications should be prepared to handle this situation. Windows will send out a WM_WTSSESSION_CHANGE message when a user session changes. In order to receive this message, your application must register its window handle by calling WTSRegisterSessionNotification.

Note Microsoft DirectDraw?and Microsoft Direct3D?applications that set the window to full screen by default will not allow Fast User Switching.

File Storage

There are two types of users on Windows XP: administrators and limited users. Administrators have read/write access to all of the hard drive. Limited users are restricted to a few areas of the hard drive where they can write data.

The only areas of the hard drive that limited users have write access to, and therefore the only place DirectX applications should store information for limited users, are the following (default) directories:

CSIDL value	Folder
CSIDL_COMMON_DOCUMENTS	C:\Documents and Settings\All Users\Documents
CSIDL_PERSONAL	C:\Documents and Settings\<username>\MyDocuments
CSIDL_COMMON_APPDATA	C:\Documents and Settings\All Users\Application Data
CSIDL_LOCAL_APPDATA	C:\Documents and Settings\<username>\Application Data

Because installation should be to the Program Files directory (CSIDL_PROGRAM_FILES) by default, only an administrator can install an application. If a limited user is trying to install an application, an informational message box should be displayed telling the user that they need administrator privileges to install.

All of these locations should be determined by passing the appropriate CSIDL to the SHGetFolderPath function, rather than being hard-coded.

Data files generated by an application should be stored with limited users in mind. Use the following table to determine where to store the data.

Data available for:	CSIDL value	Can user load, view, and alter data?	Example
All users	CSIDL_COMMON_APPDATA	NO	System configuration
Current user	CSIDL_LOCAL_APPDATA	NO	Keyboard bindings
All users	CSIDL_COMMON_DOCUMENTS	YES	Shared saved files
Current user	CSIDL_PERSONAL	YES	Private saved files

Note If the user is meant to load, view, and alter data, ensure that there is a file association and icon representative to the application.

Registry Storage

To correctly store data in the registry, use the following guidelines.

Require administrator privileges for installation.
Be sure that each registry key item is less than 64 KB of data.
Registry data can exist in HKEY_LOCAL_MACHINE or HKEY_CURRENT_USER.
HKEY_LOCAL_MACHINE
- Only administrators have access, so do not store information that limited users will need to access in HKEY_LOCAL_MACHINE.
- If you have data that few users must access, place it in HKEY_LOCAL_MACHINE.
- Store computer configuration data in HKEY_LOCAL_MACHINE.
HKEY_CURRENT_USER
- Both administrators and limited users have access.
- Any data that the "limited users" will need to access should be in HKEY_CURRENT_USER.
- Store user configuration data in HKEY_CURRENT_USER.
- When the game is first started, check the registry keys in HKEY_CURRENT_USER and make sure the default values exist.