The Microsoft® Pocket PowerPoint® application can use secondary displays if the display driver maintains certain registry keys when it is loaded and unloaded. At initialization, the driver should create a subkey for itself within the HKEY_LOCAL_MACHINE\Drivers\Display\Active key. This key is used to specify the secondary display driver’s DLL name, as well as the driver’s buffer and tap information. For more information, see Registry Keys for Display Drivers. For removable display adapters, such as PC Card–based adapters, this initialization should take place when the Device Manager calls the display driver’s XXX_Init function.
Pocket PowerPoint loads the secondary display driver’s DDI library by calling the CreateDC function with the secondary display driver’s DDI library name. For example, if the Drivers\Display\Active\Voyager\Dll subkey has the value PCARDVGA.DLL, Pocket PowerPoint calls CreateDC and passes the string PCARDVGA.DLL as an input parameter.
After the driver loads and initializes, Pocket PowerPoint calls the GetDeviceCaps function to identify the display device’s resolution and color depth. The secondary display driver typically stores this information internally. When the driver supports multiple resolutions and those resolutions are selected by a separate application, such as a Control Panel application, this information may optionally be kept in the registry.
When the secondary display driver is unloaded, it should remove the Drivers\Display\Active subkey that it created during initialization. This indicates that the driver is no longer available. For removable display adapters, this de-initialization should take place when the Device Manager calls the drivers XXX_Deinit function after the user disconnects the display adapter from the system.