How to Embed a TCanvas in External Applications

Here is a short HOWTO showing the few steps required to embed a TCanvas in an application created with toolkits as QT, FOX, MFC, and probably many more.

*** IMPORTANT: Do not call TApplication::Run() ***

• In the application constructor or in main(), create a TApplication

     // create an instance of TApplication
   
     gMyRootApp = new TApplication("My ROOT Application", &argc, argv);
   
     // tell application to return from run
     gMyRootApp->SetReturnFromRun(true);

• Create a timer to process Root events, e.g.:

     void MyWindow::OnRefreshTimer() {
   
        // Process Root events when a timer message is received
   
        gApplication->StartIdleing();
        gSystem->InnerLoop();
        gApplication->StopIdleing();
     }

• Get the id of the window where you want to embed the TCanvas :

     void MyWindow::Create() {
   
        // Add this window to TVirtualX list of windows
        // in return get its TVirtualX identifier
        int wid = gVirtualX->AddWindow((ULong_t)getid(), getWidth(), getHeight());
   
        // Create a new TCanvas, specifying this window's id as parent
        fCanvas = new TCanvas("fCanvas", getWidth(), getHeight(), wid);
     }

• Forward messages to the Canvas, e.g.:

     void MyWindow::OnPaint() {
   
        // Handle Paint events
   
        if (fCanvas) fCanvas->Update();
     }
   
     void MyWindow::OnSize() {
   
        // Handle Resize events
   
        if (fCanvas) fCanvas->Resize();
     }
   
     void MyWindow::OnMouseMove() {
   
        // Handle Mouse move events
   
        if (!fCanvas) return;
   
        if (ev->state & LEFTBUTTONMASK)
           fCanvas->HandleInput(kButton1Motion, ev->win_x, ev->win_y);
        else 
           fCanvas->HandleInput(kMouseMotion, ev->win_x, ev->win_y);
     }
   
     void MyWindow::OnLMouseDown() {
   
        // Handle Mouse Left button down event
   
        if (fCanvas) fCanvas->HandleInput(kButton1Down, ev->x, ev->y);
     }

Screenshots of TCanvas embedded in external application

MFC & ROOT
Qt & ROOT
FOX & ROOT