Disconnect and Reconnect Displays Programmatically

Question

Question: What is the best way to programmatically disconnect and reconnect displays programmatically?

The Goal: Kill the video output (black screen with no backlight) on a display and later turn it back on. Imagine unplugging the video cord from the monitor, then plugging it back in.

My Attempt:

// Get the monitor to disable
uint iDevNum = 0;
DISPLAY_DEVICE displayDevice = new DISPLAY_DEVICE();
displayDevice.cb = Marshal.SizeOf(displayDevice);
EnumDisplayDevices(null, iDevNum, ref displayDevice, 0))

DEVMODE devMode = new DEVMODE();
EnumDisplaySettings(displayDevice.DeviceName, 0, ref devMode);

//
// Do something here to disable this display device!
//

// Save the display settings
ChangeDisplaySettingsEx(displayDevice.DeviceName, ref devMode, 
    IntPtr.Zero, ChangeDisplaySettingsFlags.CDS_NONE, IntPtr.Zero);

I can interact with each display, but I can't figure out how to disconnect one.

It is similar to "Disconnect this display" in the Screen Resolution properties in Windows 7:

Windows 7 Screen Resolution Properties

Notes:

Turning off video output on all displays won't work because I need the other monitors to stay on.
The desktop area on the "dead" display does NOT need to be usable when it is off. Also, it is fine if windows move around.

References:

score 3 · Accepted Answer · edited May 23 '17 at 12:34

1) Get MultiMonitorHelper from here: https://github.com/ChrisEelmaa/MultiMonitorHelper/tree/master

2) Extend Win7Display to disconnect the display:

using MultiMonitorHelper.DisplayModels.Win7.Enum;
using MultiMonitorHelper.DisplayModels.Win7.Struct;

/// <summary>
/// Disconnect a display.
/// </summary>
public void DisconnectDisplay(int displayNumber)
{
    // Get the necessary display information
    int numPathArrayElements = -1;
    int numModeInfoArrayElements = -1;
    StatusCode error = CCDWrapper.GetDisplayConfigBufferSizes(
        QueryDisplayFlags.OnlyActivePaths,
        out numPathArrayElements,
        out numModeInfoArrayElements);

    DisplayConfigPathInfo[] pathInfoArray = new DisplayConfigPathInfo[numPathArrayElements];
    DisplayConfigModeInfo[] modeInfoArray = new DisplayConfigModeInfo[numModeInfoArrayElements];
    error = CCDWrapper.QueryDisplayConfig(
        QueryDisplayFlags.OnlyActivePaths,
        ref numPathArrayElements,
        pathInfoArray,
        ref numModeInfoArrayElements,
        modeInfoArray,
        IntPtr.Zero);
    if (error != StatusCode.Success)
    {
        // QueryDisplayConfig failed
    }

    // Check the index
    if (pathInfoArray[displayNumber].sourceInfo.modeInfoIdx < modeInfoArray.Length)
    {
        // Disable and reset the display configuration
        pathInfoArray[displayNumber].flags = DisplayConfigFlags.Zero;
        error = CCDWrapper.SetDisplayConfig(
            pathInfoArray.Length,
            pathInfoArray,
            modeInfoArray.Length,
            modeInfoArray,
            (SdcFlags.Apply | SdcFlags.AllowChanges | SdcFlags.UseSuppliedDisplayConfig));
        if (error != StatusCode.Success)
        {
            // SetDisplayConfig failed
        }
    }
}

3) Extend Win7Display to reconnect the display using an answer from this post:

using System.Diagnostics;

/// <summary>
/// Reconnect all displays.
/// </summary>
public void ReconnectDisplays()
{
    DisplayChanger.Start();
}

private static Process DisplayChanger = new Process
{
    StartInfo =
    {
        CreateNoWindow = true,
        WindowStyle = ProcessWindowStyle.Hidden,
        FileName = "DisplaySwitch.exe",
        Arguments = "/extend"
    }
};

4) Update the methods in IDisplay.

5) Implement the methods:

IDisplayModel displayModel = DisplayFactory.GetDisplayModel();
List<IDisplay> displayList = displayModel.GetActiveDisplays().ToList();

displayList[0].DisconnectDisplay(0);
displayList[0].ReconnectDisplays();

The GitHub link does not work anymore, any idea if this is still available — Horst Walter, Jun 16 '23 at 09:40
@HorstWalter Try searching GitHub for other repos with the same name. One of them might be similar. — AndrewRalon, Jun 20 '23 at 19:29

score 2 · Answer 2 · edited May 23 '17 at 12:10

There's a github project that I STILL haven't got around, but it's a starting point. You need to use Win7 specific API in order to change settings. ChangeDisplaySettings won't work.

Have a look: https://github.com/ChrisEelmaa/MultiMonitorHelper

This is what you need to do:

update the IDisplay interface to support TurnOff() method,

and then call it:

var displayModel = DisplayFactory.GetDisplayModel();
var displayList = displayModel.GetActiveDisplays().ToList();
var firstDisplay = displayList[0].TurnOff();

How to implement TurnOff()? I WOULD imagine this is how(I might be wrong here now):

You need to break the connection between GPU & monitor through breaking the "paths". You can break path between source and target like this:

Call SetDisplayConfig() and pass inside specific paths and make sure you map out the DISPLAYCONFIG_PATH_ACTIVE from the DISPLAY_PATH_INFO structure flags integer.

http://msdn.microsoft.com/en-us/library/windows/hardware/ff553945(v=vs.85).aspx

Sorry for not being more helpful, but this is pretty hardcore stuff, it took me quite a while to even understand the basics of that API. It's a starting point :-),

take a look at the example how to rotate specific monitor in Win7: How do I set the monitor orientation in Windows 7?

In all honesty, just wrap the DisplaySwitch.exe for Win7, and pass /internal or /external(depending if you want to disable/enable first/second monitor), this might or might not work for >2 monitors.

your github is down, would it be possible for you to reopen it — Anthony, May 16 '18 at 23:23

Disconnect and Reconnect Displays Programmatically

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