webgui: let specify place where canvas should be shown

By defauly, ROOT will try to crate local window with CEF or Qt5.
If not available, default browser will be started.
If place is specified, it should be program name like:
   canvas->Show("/usr/bin/opera");
   canvas->Show("firefox");

One could show canvas in several different places.

graf2d/gpad/v7/inc/ROOT/TCanvas.hxx

@@ -125,8 +125,8 @@ public:
    /// Remove an object from the list of primitives.
    // TODO: void Wipe();
 
-   /// Actually display the canvas.
-   void Show();
+   /// Display the canvas.
+   void Show(const std::string &where = "");
 
    // Indicates that any object was modified
    void Modified();

graf2d/gpad/v7/inc/ROOT/TVirtualCanvasPainter.hxx

@@ -62,6 +62,8 @@ public:
    /// perform special action when drawing is ready
    virtual void DoWhenReady(const std::string &, const std::string &) = 0;
 
+   virtual void NewDisplay(const std::string &where) = 0;
+
    /// Loads the plugin that implements this class.
    static std::unique_ptr<TVirtualCanvasPainter> Create(const TCanvas &canv, bool batch_mode = false);
 };

graf2d/gpad/v7/src/TCanvas.cxx

@@ -73,17 +73,22 @@ std::shared_ptr<ROOT::Experimental::TCanvas> ROOT::Experimental::TCanvas::Create
    return pCanvas;
 }
 
-void ROOT::Experimental::TCanvas::Show()
+void ROOT::Experimental::TCanvas::Show(const std::string &where)
 {
-   if (fPainter)
+   if (fPainter) {
+      if (!where.empty()) fPainter->NewDisplay(where);
       return;
+   }
+
    bool batch_mode = gROOT->IsBatch();
    if (!fModified)
       fModified = 1; // 0 is special value, means no changes and no drawings
 
    fPainter = Internal::TVirtualCanvasPainter::Create(*this, batch_mode);
-   if (fPainter)
-      fPainter->CanvasUpdated(fModified, false);
+   if (fPainter) {
+      fPainter->NewDisplay(where);
+      fPainter->CanvasUpdated(fModified, true); // trigger async display
+   }
 }
 
 void ROOT::Experimental::TCanvas::SaveAs(const std::string &filename)

gui/canvaspainter/v7/src/TCanvasPainter.cxx

@@ -201,7 +201,6 @@ class TCanvasPainter : public THttpWSHandler,
    ROOT::Experimental::Internal::TDrawable *FindDrawable(const ROOT::Experimental::TCanvas &can, const std::string &id);
 
    void CreateHttpServer(Bool_t with_http = kFALSE);
-   void PopupBrowser();
    void CheckDataToSend();
 
    bool WaitWhenCanvasPainted(uint64_t ver);
@@ -222,7 +221,6 @@ class TCanvasPainter : public THttpWSHandler,
    {
       CreateHttpServer();
       gServer->Register("/web7gui", this);
-      PopupBrowser();
    }
 
    virtual bool IsBatchMode() const { return fBatchMode; }
@@ -236,6 +234,9 @@ class TCanvasPainter : public THttpWSHandler,
    /// perform special action when drawing is ready
    virtual void DoWhenReady(const std::string &cmd, const std::string &arg) final;
 
+   // open new display for the canvas
+   virtual void NewDisplay(const std::string &where) override;
+
    // void ReactToSocketNews(...) override { SendCanvas(); }
 
    /** \class CanvasPainterGenerator
@@ -302,18 +303,18 @@ void TCanvasPainter::CreateHttpServer(Bool_t with_http)
    gServer->CreateEngine(TString::Format("http:%s?websocket_timeout=10000", port).Data());
 }
 
-void TCanvasPainter::PopupBrowser()
+void TCanvasPainter::NewDisplay(const std::string &where)
 {
    TString addr;
 
    Func_t symbol_qt5 = gSystem->DynFindSymbol("*", "webgui_start_browser_in_qt5");
-   if (symbol_qt5) {
+   if (symbol_qt5 && (where.empty() || (where == "qt5") || (where == "native"))) {
       typedef void (*FunctionQt5)(const char *, void *, bool);
 
       addr.Form("://dummy:8080/web7gui/%s/draw.htm?longpollcanvas%s", GetName(), (IsBatchMode() ? "&batch_mode" : ""));
       // addr.Form("example://localhost:8080/Canvases/%s/draw.htm", Canvas()->GetName());
 
-      Info("PopupBrowser", "Show canvas in Qt5 window:  %s", addr.Data());
+      Info("NewDisplay", "Show canvas in Qt5 window:  %s", addr.Data());
 
       FunctionQt5 func = (FunctionQt5)symbol_qt5;
       func(addr.Data(), gServer, IsBatchMode());
@@ -323,13 +324,14 @@ void TCanvasPainter::PopupBrowser()
    Func_t symbol_cef = gSystem->DynFindSymbol("*", "webgui_start_browser_in_cef3");
    const char *cef_path = gSystem->Getenv("CEF_PATH");
    const char *rootsys = gSystem->Getenv("ROOTSYS");
-   if (symbol_cef && cef_path && !gSystem->AccessPathName(cef_path) && rootsys) {
+   if (symbol_cef && cef_path && !gSystem->AccessPathName(cef_path) && rootsys &&
+       (where.empty() || (where == "cef") || (where == "native"))) {
       typedef void (*FunctionCef3)(const char *, void *, bool, const char *, const char *);
 
       // addr.Form("/web7gui/%s/draw.htm?cef_canvas%s", GetName(), (IsBatchMode() ? "&batch_mode" : ""));
       addr.Form("/web7gui/%s/draw.htm?cef_canvas%s", GetName(), (IsBatchMode() ? "&batch_mode" : ""));
 
-      Info("PopupBrowser", "Show canvas in CEF window:  %s", addr.Data());
+      Info("NewDisplay", "Show canvas in CEF window:  %s", addr.Data());
 
       FunctionCef3 func = (FunctionCef3)symbol_cef;
       func(addr.Data(), gServer, IsBatchMode(), rootsys, cef_path);
@@ -343,12 +345,14 @@ void TCanvasPainter::PopupBrowser()
 
    TString exec;
 
-   if (gSystem->InheritsFrom("TMacOSXSystem"))
+   if (!where.empty() && (where != "native"))
+      exec.Form("%s %s", where.c_str(), addr.Data());
+   else if (gSystem->InheritsFrom("TMacOSXSystem"))
       exec.Form("open %s", addr.Data());
    else
       exec.Form("xdg-open %s &", addr.Data());
 
-   Info("PopupBrowser", "Show canvas in browser with cmd:  %s", exec.Data());
+   Info("NewDisplay", "Show canvas in browser with cmd:  %s", exec.Data());
 
    gSystem->Exec(exec);
 }
@@ -360,7 +364,8 @@ void TCanvasPainter::CanvasUpdated(uint64_t ver, bool async)
 
    CheckDataToSend();
 
-   if (!async) WaitWhenCanvasPainted(ver);
+   if (!async)
+      WaitWhenCanvasPainted(ver);
 }
 
 bool TCanvasPainter::WaitWhenCanvasPainted(uint64_t ver)
@@ -371,15 +376,19 @@ bool TCanvasPainter::WaitWhenCanvasPainted(uint64_t ver)
    bool had_connection = false;
 
    while (true) {
-      if (fWebConn.size() > 0) had_connection = true;
-      if ((fWebConn.size()==0) && (had_connection || (cnt>1000))) return false; // wait ~1 min if no new connection established
-      if (fSnapshotDelivered >= ver) { printf("PAINT READY!!!\n"); return true; }
+      if (fWebConn.size() > 0)
+         had_connection = true;
+      if ((fWebConn.size() == 0) && (had_connection || (cnt > 1000)))
+         return false; // wait ~1 min if no new connection established
+      if (fSnapshotDelivered >= ver) {
+         printf("PAINT READY!!!\n");
+         return true;
+      }
       gSystem->ProcessEvents();
-      gSystem->Sleep((++cnt<500) ? 1 : 100); // increase sleep interval when do very often
+      gSystem->Sleep((++cnt < 500) ? 1 : 100); // increase sleep interval when do very often
    }
 
    return false;
-
 }
 
 void TCanvasPainter::DoWhenReady(const std::string &cmd, const std::string &arg)

tutorials/v7/draw_v6.cxx

@@ -35,7 +35,9 @@ void draw_v6()
    auto canvas = Experimental::TCanvas::Create("v7 TCanvas showing a v6 TGraph");
    canvas->Draw(gr);
 
-   canvas->Show();
+   canvas->Show(); // one could use canvas->Show("/usr/bin/opera"); or canvas->Show("firefox");
+
+   canvas->Update(); // wait until painting is finished
 
    canvas->SaveAs("draw.png"); // only .svg and .png are supported for the moment, asynchron
 }