Multiple Monitor System Metrics
The GetSystemMetrics function returns values for the primary monitor, except for SM_CXMAXTRACK and SM_CYMAXTRACK, which refer to the entire desktop. The following metrics are the same for all device drivers: SM_CXCURSOR, SM_CYCURSOR, SM_CXICON, SMCYICON. The following display capabilities are the same for all monitors: LOGPIXELSX, LOGPIXELSY, DESTOPHORZRES, DESKTOPVERTRES.
GetSystemMetrics also has constants that refer only to a Multiple Monitor system. SM_XVIRTUALSCREEN and SM_YVIRTUALSCREEN identify the upper-left corner of the virtual screen, SM_CXVIRTUALSCREEN and SM_CYVIRTUALSCREEN are the vertical and horizontal measurements of the virtual screen, SM_CMONITORS is the number of monitors attached to the desktop, and SM_SAMEDISPLAYFORMAT indicates whether all the monitors on the desktop have the same color format.
To get information about a single display monitor or all of the display monitors in a desktop, use EnumDisplayMonitors. The rectangle of the desktop window returned by GetWindowRect or GetClientRect is always equal to the rectangle of the primary monitor, for compatibility with existing applications. Thus, the result of
rc.left = 0; rc.top = 0; rc.right = GetSystemMetrics (SM_CXSCREEN); rc.bottom = GetSystemMetrics (SM_CYSCREEN);
To change the work area of a monitor, call SystemParametersInfo with SPI_SETWORKAREA and pvParam pointing to a RECT structure that is on the desired monitor. If pvParam is NULL, the work area of the primary monitor is modified. Using SPI_GETWORKAREA always returns the work area of the primary monitor. To get the work area of a monitor other than the primary monitor, call GetMonitorInfo.