I am writing an application where it would be helpful to automatically switch between having Windows XP's desktop in dualview or cloned. The application uses a small wxWidgets window for the GUI. It would be nice to have a button within the GUI that could easily switch between dualview and cloned.
Is there a c/c++ library that gives access to controlling dualview or cloned?
Check out this script which, as far as I can tell, is supposed to enable or disable multiview. While it is written in a scripting language, it does leverage normal WinAPI functions, so you should be able to find out what is happening by looking at them.
As far as I can tell, it appears that disabling a second monitor is done by calling ChangeDisplaySettingsEx on the second monitor and providing a width, height, colour depth and refresh rate of 0. To reenable it, one would call ChangeDisplaySettingsEx a second time with valid parameters presumably.
Anyway it would probably be best to try the script (the interpreter is available for free on the homepage) and see if it achieves the functionality you're looking for (note that the script is hardcoded for two particular monitors, you will have to replace them with the names of your monitors to get it to work).
The following code sort of works. It doesn't keep the monitor resolution.
void AppFrame::OnButtonModify(wxCommandEvent& event)
{
static bool bSwitch = false;
if (bSwitch)
{
ExtendExternalDisplay();
}
else
{
CloneExternalDisplay();
}
bSwitch = !bSwitch;
}
void AppFrame::ExtendExternalDisplay()
{
int nModeSwitch = NULL;
DEVMODE dmPrimary, dmSecondary, dmThird, savedmSecondary;
#define szPrimaryDisplay TEXT( "\\\\.\\DISPLAY1" )
#define szSecondaryDisplay TEXT( "\\\\.\\DISPLAY2" )
#define szThirdDisplay TEXT( "\\\\.\\DISPLAY3" )
ZeroMemory( &dmPrimary, sizeof(dmPrimary) );
dmPrimary.dmSize = sizeof(dmPrimary);
ZeroMemory( &dmSecondary, sizeof(dmSecondary) );
dmSecondary.dmSize = sizeof(dmSecondary);
ZeroMemory( &dmThird, sizeof(dmThird) );
dmThird.dmSize = sizeof(dmThird);
ZeroMemory( &dmThird, sizeof(dmThird) );
dmThird.dmSize = sizeof(dmThird);
BOOL result;
HDC handle;
DWORD iDevNum = 0;
DWORD dwFlags = 0;
DISPLAY_DEVICE lpDisplayDevice, lpDisplayDeviceOne, lpDisplayDeviceTwo;
ZeroMemory(&lpDisplayDevice, sizeof(lpDisplayDevice));
ZeroMemory(&lpDisplayDeviceOne, sizeof(lpDisplayDeviceOne));
ZeroMemory(&lpDisplayDeviceTwo, sizeof(lpDisplayDeviceTwo));
lpDisplayDevice.cb = sizeof(lpDisplayDevice);
lpDisplayDeviceOne.cb = sizeof(lpDisplayDeviceOne);
lpDisplayDeviceTwo.cb = sizeof(lpDisplayDeviceTwo);
// All this does is confirm the number of display devices the graphics board is capable of handling
while(EnumDisplayDevices(NULL, iDevNum, &lpDisplayDevice, dwFlags))
{
if (iDevNum == 0)
{
lpDisplayDeviceOne = lpDisplayDevice;
TRACE("DeviceName: '%s'\n", lpDisplayDeviceOne.DeviceName);
TRACE("DeviceString: '%s'\n", lpDisplayDeviceOne.DeviceString);
TRACE("Flags: %08X %s%s\n", lpDisplayDeviceOne.StateFlags,((lpDisplayDeviceOne.StateFlags & DISPLAY_DEVICE_ATTACHED_TO_DESKTOP) ? "Desktop " : ""), ((lpDisplayDeviceOne.StateFlags & DISPLAY_DEVICE_PRIMARY_DEVICE) ? "Primary" : ""));
}
if (iDevNum == 1)
{
lpDisplayDeviceTwo = lpDisplayDevice;
TRACE("DeviceName: '%s'\n", lpDisplayDeviceTwo.DeviceName);
TRACE("DeviceString: '%s'\n", lpDisplayDeviceTwo.DeviceString);
TRACE("Flags: %08X %s%s\n", lpDisplayDeviceTwo.StateFlags,((lpDisplayDeviceTwo.StateFlags & DISPLAY_DEVICE_ATTACHED_TO_DESKTOP) ? "Desktop " : ""), ((lpDisplayDeviceTwo.StateFlags & DISPLAY_DEVICE_PRIMARY_DEVICE) ? "Primary" : ""));
}
iDevNum ++;
}
// load DISPLAY1 monitor information // ENUM_CURRENT_SETTINGS
if (!EnumDisplaySettings(szPrimaryDisplay, ENUM_REGISTRY_SETTINGS, (DEVMODE*)&dmPrimary))
{
TRACE("EnumDisplaySettings unable to enumerate primary display\n");
return;
}
if (!EnumDisplaySettings(szSecondaryDisplay, ENUM_REGISTRY_SETTINGS, (DEVMODE*)&dmSecondary))
TRACE("EnumDisplaySettings unable to enumerate secondary display display\n");
// these don't enumerate in clone mode
if (!EnumDisplaySettings(szSecondaryDisplay, ENUM_CURRENT_SETTINGS, (DEVMODE*)&savedmSecondary))
TRACE("EnumDisplaySettings unable to enumerate secondary display using ENUM_CURRENT_SETTINGS settings\n");
// disable a display, doesn't work
// nModeSwitch = ChangeDisplaySettingsEx (szSecondaryDisplay, NULL, NULL, NULL, NULL);
// CDdx::ErrorDisplayDevice(nModeSwitch); // test and TRACE result
dmPrimary.dmFields = DM_POSITION;
dmPrimary.dmPosition.x = 0; // set DISPLAY1 as the primary display
dmPrimary.dmPosition.y = 0; // set DISPLAY1 as the primary display
// set DISPLAY1 as primary display (dmPosition.x = 0)
nModeSwitch = ChangeDisplaySettingsEx (szPrimaryDisplay, (DEVMODE*)&dmPrimary, NULL, (CDS_UPDATEREGISTRY | CDS_NORESET), NULL);
// CDdx::ErrorDisplayDevice(nModeSwitch); // test and TRACE result
// despite the other lines of code this next line is neccesary to wake the video projector
dmSecondary = dmPrimary;
dmSecondary.dmFields = DM_POSITION | DM_PELSWIDTH | DM_PELSHEIGHT;
dmSecondary.dmPosition.x = dmPrimary.dmPelsWidth + 1;
dmSecondary.dmPosition.y = 0;
dmSecondary.dmPelsWidth = dmPrimary.dmPelsWidth; // resize the primary display to match the secondary display
dmSecondary.dmPelsHeight = dmPrimary.dmPelsHeight; // resize the primary display to match the secondary display
nModeSwitch = ChangeDisplaySettingsEx (szSecondaryDisplay, (DEVMODE*)&dmSecondary, NULL, (CDS_UPDATEREGISTRY | CDS_NORESET), NULL);
// CDdx::ErrorDisplayDevice(nModeSwitch); // test and TRACE result
// load DISPLAY3 monitor information
if (!EnumDisplaySettings(szThirdDisplay, ENUM_CURRENT_SETTINGS, (DEVMODE*)&dmThird))
{
TRACE("EnumDisplaySettings unable to enumerate third display display\n");
}
else
{
dmThird.dmPelsWidth = dmSecondary.dmPelsWidth; // resize the primary display to match the secondary display
dmThird.dmPelsHeight = dmSecondary.dmPelsHeight; // resize the primary display to match the secondary display
dmThird.dmPosition.x = -dmThird.dmPelsWidth; // set DISPLAY3 as the third display
dmPrimary.dmPosition.y = 0; // set DISPLAY1 as the third display
// set DISPLAY3 as third display (-dmThird.dmPelsWidth)
nModeSwitch = ChangeDisplaySettingsEx (szThirdDisplay, (DEVMODE*)&dmThird, NULL, (CDS_UPDATEREGISTRY | CDS_NORESET), NULL);
// CDdx::ErrorDisplayDevice(nModeSwitch); // test and TRACE result
}
// really important line makes the whole thing happen
nModeSwitch = ChangeDisplaySettingsEx (NULL, NULL, NULL, 0, NULL);
// CDdx::ErrorDisplayDevice(nModeSwitch); // test and TRACE result
}
void AppFrame::CloneExternalDisplay()
{
int nModeSwitch = NULL;
DEVMODE dmPrimary, dmSecondary, dmThird;
#define szPrimaryDisplay TEXT( "\\\\.\\DISPLAY1" )
#define szSecondaryDisplay TEXT( "\\\\.\\DISPLAY2" )
#define szThirdDisplay TEXT( "\\\\.\\DISPLAY3" )
ZeroMemory( &dmPrimary, sizeof(dmPrimary) );
dmPrimary.dmSize = sizeof(dmPrimary);
ZeroMemory( &dmSecondary, sizeof(dmSecondary) );
dmSecondary.dmSize = sizeof(dmSecondary);
ZeroMemory( &dmThird, sizeof(dmThird) );
// load DISPLAY1 monitor information
if (!EnumDisplaySettings(szPrimaryDisplay, ENUM_CURRENT_SETTINGS, (DEVMODE*)&dmPrimary))
{
TRACE("EnumDisplaySettings unable to enumerate primary display\n");
return;
}
if (!EnumDisplaySettingsEx(szSecondaryDisplay, ENUM_REGISTRY_SETTINGS, (DEVMODE*)&dmSecondary, 0))
TRACE("EnumDisplaySettings unable to enumerate secondary display display\n");
dmPrimary.dmFields = DM_POSITION;
dmPrimary.dmPosition.x = 0; // set DISPLAY1 as the primary display
dmPrimary.dmPosition.y = 0; // set DISPLAY1 as the primary display
// set DISPLAY1 as primary display (dmPosition.x = 0)
nModeSwitch = ChangeDisplaySettingsEx (szPrimaryDisplay, (DEVMODE*)&dmPrimary, NULL, (CDS_UPDATEREGISTRY | CDS_NORESET), NULL);
// CDdx::ErrorDisplayDevice(nModeSwitch); // test and TRACE result
// this should disable display
dmSecondary.dmFields = DM_PELSWIDTH|DM_PELSHEIGHT;
dmSecondary.dmPelsWidth = 0; //dmPrimary.dmPelsWidth; // resize the primary display to match the secondary display
dmSecondary.dmPelsHeight = 0;//dmPrimary.dmPelsHeight; // resize the primary display to match the secondary display
// this should clone the display
dmSecondary.dmFields |= DM_POSITION;
dmSecondary.dmPosition.x = 0; // set DISPLAY1 as the primary display
dmSecondary.dmPosition.y = 0; // set DISPLAY1 as the primary display
nModeSwitch = ChangeDisplaySettingsEx (szSecondaryDisplay, (DEVMODE*)&dmSecondary, NULL, (CDS_UPDATEREGISTRY | CDS_NORESET), NULL);
// CDdx::ErrorDisplayDevice(nModeSwitch); // test and TRACE result
nModeSwitch = ChangeDisplaySettingsEx (NULL, NULL, NULL, 0, NULL); // set DISPLAY1 as the primary display
// CDdx::ErrorDisplayDevice(nModeSwitch); // test and TRACE result
}