How to display Unity scene in a Qt window

I tried the same thing today and found a working solution based on the example from unity command line options page: http://docs.unity3d.com/Manual/CommandLineArguments.html.

My Code:

    //GET FILE
     QString fileName = QFileDialog::getOpenFileName(this,
         tr("Open Unity Build"), "D:/tmp/", tr("Unity Build (*.exe)"));
 
     // PASS ARGS
     QString _args = QString("-parentHWND %1 -force-opengl").arg(ui->unityWidget->effectiveWinId());
 
     //
     PROCESS_INFORMATION procInfo = {0};
     STARTUPINFO startupInfo = {0};
     startupInfo.cb = sizeof(startupInfo);
     startupInfo.dwFlags = STARTF_USESTDHANDLES;
     startupInfo.hStdInput = GetStdHandle(STD_INPUT_HANDLE);
     startupInfo.hStdOutput = GetStdHandle(STD_OUTPUT_HANDLE);
     startupInfo.hStdError = GetStdHandle(STD_ERROR_HANDLE);
 
     //
     HWND hwnd = (HWND) ui->unityWidget->effectiveWinId();
     LPWSTR cmd = (LPWSTR) fileName.utf16();
     LPWSTR args = (LPWSTR) _args.utf16();
 
     BOOL bProcessStarted = CreateProcess(cmd,args , NULL, NULL, TRUE, CREATE_NO_WINDOW,
              NULL, NULL, &startupInfo, &procInfo);
     if(!bProcessStarted) ;// TODO: show error
 
     //WAIT FOR START
     qint64 before = QDateTime::currentMSecsSinceEpoch();
     Sleep(100);
 //  WaitForInputIdle(ProcessInfo.hProcess, INFINITE);
     qint64 after = QDateTime::currentMSecsSinceEpoch();
     qDebug() << "Waited " << (after-before);
 
     //GET UNITY WINDOW HANDLE
     EnumChildWindows(hwnd, MainWindow::EnumChildGet, 0);

It Only works on Windows and Unity 4.5+. I hope it helps! I needed a whole workday to make it work.

Hi ahrakos,

thanks for your answer. Sorry for beeing late, I have made some tries to get to my solution. Actually, I think that I am very close to what expected, just one little thing to solve, and the solution will be perfect. After reading my question, I recognize that there is something important on which I haven't been clear enough, that is why you gave me this answer. When I talk about catching the unity output, I mean that Qt must not only know the image handle, but it must also be the window itself. So, a pixels copy is necessary (I suppose...). Anyway ahrakos, I am sure some people will be very interested by your solution which is simpler and more natural.

So here are a few hints for people with the same issue : - First, I implemented a communication channel between unity and Qt processes via a shared memory with a plugin (http://qt-project.org/doc/qt-4.8/ipc-sharedmemory.html) - Then, I implemented in another plugin a command to get the handle of unity window and hiding it (http://stackoverflow.com/questions/1888863/how-to-get-main-window-handle-from-process-id) - Now I can hide the unity window, send it some commands and kill it at the end of the Qt process.

Last thing that I need, is to be able to retrieve pixels matrix from unity. I have succeeded to get the rendering texture to create a png file (using Texture2D.ReadPixels). Now, instead of getting the file, I have to copy the unity image in the shared memory which will be read back by Qt for displaying. I guess that I will have to use the functions Texture.GetNativeTexturePtr() and IntPtr.ToPointer, but I am a bit stuck for completion.

Honestly, I have no idea of the output performance. So many copies to do is not what we could call an optimized process, but for a prototype, we can live with that.

UPDATE: Corrected the link

For displaying, you need to use following:

-parentHWND (Windows only) - Embeds Windows Standalone application into another application, you have to pass parent application’s window
handle to Windows Standalone application. See this example for more information. http://docs.unity3d.com/uploads/Examples/EmbeddedWindow.zip

For communication, you can use Shared Memory via QSharedMemory, or better QLocalSocket with native plugin. You can also use loopback TCP/IP or Registry Hives. It's up to you.

Interesting topic. I implemented a Qt application in C++ with embedded unity player. There is just one point not working and I see the same problem in EmbeddedWindow.zip C# application: mouse interaction with embedded unity player is not working at stat-up. Just after the application window resize the mouse interaction works. Any idea?

Regards Gianni

Good morning, could someone explain better how to integrate Unity in a QT window? I am new in using Qt and I don't know where to start. Thanks.