Multiple Monitor Support

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Multiple Monitor Support

Whilst working on a screensaver for a client I came across the problem of multiple monitors. No, not myself as I am too poor to have two monitors on one system. However the client has a PC set up grand enough to make Cape Canaveral quake in its cowboy boots and run like a buffalo.

For those of you not aware of the problems of multiple monitors let me explain. Say we take Mr. Monitor here. He uses points to provide a location on his screen. Using an X and a Y co-ordinate like ( 20, 100 ). These points are taken relative to (0,0) which is the very top-left hand corner of the screen.

This is fine, however when creating a screen saver you need to know the boundaries that the screen saver can go up to. There is no point in making a screen saver that over-flows the screen. So for getting the screen parameters you may use this:

CRect rect;
  Rect.left = 0;
  Rect.top = 0;
  Rect.right = rect.left + ::GetSystemMetrics(SM_CYSCREEN);
  Rect.bottom = rect.top + ::GetSystemMetrics(SM_CXSCREEN);

This code will provide the bottom and right hand boundaries as well as defining the top and left as zero. From this you can create your window size using this:

const char* myWndClass = AfxRegisterWndClass(CS_HREDRAW|CS_VREDRAW|
  CSSAVEBITS|CSDBLCLKS, NULL);

  CWnd::CreateEx(WS_EX_TOPMOST, myWndClass, " ", WS_POPUP | WS_VISIBLE, 
  rect.left, rect.top, rectWidth(), rect.Height(), hwndParent, NULL );

If anyone using a multiple monitor system views the app with this code they will only see the screensaver on their primary monitor and will view the desktop on the others. For this we need to include a header file and change a little bit of code.

The header file is multimon.h and is available from Microsoft. Or in the source zip on this page. Add Multimon.h to your project and add the line:

#include "multimon.h"

to your Window class source file.

Then we change the code from:

CRect rect;
  Rect.left = 0;
  Rect.top = 0;
  Rect.right = rect.left + ::GetSystemMetrics(SM_CYSCREEN);
  Rect.bottom = rect.top + ::GetSystemMetrics(SM_CXSCREEN);

To

CRect rect;
  Rect.left = ::GetSystemMetrics(SM_XVIRTUALSCREEN);
  Rect.top = ::GetSystemMetrics(SM_YVIRTUALSCREEN);
  Rect.right = rect.left + ::GetSystemMetrics(SM_CYVIRTUALSCREEN);
  Rect.bottom = rect.top + ::GetSystemMetrics(SM_CXVIRTUALSCREEN);

That's it! The screensaver will now run over the entire virtual desktop.

Updates:

July 2nd 2002 - Added Demo Projects. Both in zip folder, one for single display support and one for multi monitor support.