Display Duplicate optionally with three monitors connected in the OS

Question

I am trying to display with 3 monitors, ordered in 1,2,3.  I need to config the 3 monitors by programming. How to clone or duplicate 2 of the 3 monitors optionally? For example 1|2 or 2|3 or 1|3 duplicate?
I do not know which API I can use to do this function. Do you have idea or sample code for reference?
Thanks!

Answer 1

Hello,

Take 1|2 duplicate as an example.

1. Find active path (associate with monitor 1) via DISPLAYCONFIG_PATH_ACTIVE which indicates that the path is active and part of the desktop.
2. Find available target (associate with monitor 2) via targetAvailable. It has a different targetInfo.id (compared to active path's targetInfo.id).
3. Assign the same source id and modeInfoIdx to the path you target. Set DISPLAYCONFIG_PATH_ACTIVE flat to enable this path. Call SetDisplayConfig to duplicate. (clone)

The following is an example you can refer to:

#include <iostream>  
#include <windows.h>  
#include <vector>  
  
int main()  
{  
 UINT32 cPath = 0;  //path count  
 UINT32 cMode = 0;  //mode count  
 HRESULT hr;  
 UINT32 activePathIndex = 0;  
 UINT32 activeTargetId = 0;  
  
 hr = GetDisplayConfigBufferSizes(QDC_ALL_PATHS, &cPath, &cMode);  
 std::vector<DISPLAYCONFIG_PATH_INFO> pathArray(cPath);  
 std::vector<DISPLAYCONFIG_MODE_INFO> modeArray(cMode);  
 hr = QueryDisplayConfig(QDC_ALL_PATHS, &cPath, &pathArray[0], &cMode, &modeArray[0], NULL);  
  
 for (UINT32 i = 0; i < cPath; i++)  
 {  
 if (pathArray[i].flags & DISPLAYCONFIG_PATH_ACTIVE)  
 {  
 activePathIndex = i;  
 activeTargetId = pathArray[i].targetInfo.id;  
 printf("activePathIndex: %d, activeTargetId: %d\n", i, activeTargetId);  
 continue;  
 }  
  
 if (activeTargetId == pathArray[i].targetInfo.id)  
 continue;  
  
 if (!pathArray[i].targetInfo.targetAvailable)  
 continue;  
  
 pathArray[i].flags |= DISPLAYCONFIG_PATH_ACTIVE;  
 pathArray[i].sourceInfo.modeInfoIdx = pathArray[0].sourceInfo.modeInfoIdx;   //same source  
 pathArray[i].sourceInfo.id = pathArray[0].sourceInfo.id;       //same source  
  
 hr = SetDisplayConfig(cPath, &pathArray[0], cMode, &modeArray[0], SDC_APPLY | SDC_USE_SUPPLIED_DISPLAY_CONFIG | SDC_ALLOW_CHANGES | SDC_SAVE_TO_DATABASE);  
 if (hr == ERROR_SUCCESS) {   
 printf("Duplicate succeed !");  
 break;  
 }  
 }  
}  

Thank you!

Answer 2

Hi @Rita Han - MSFT , I can't get this to work and I'm desperate need to get this working, could you please help me with it. Thanks is advance !