webgui: provide callback argument for Canvas::SaveAs method

Callback function called when file is created (or command fails)

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

@@ -16,15 +16,15 @@
 #ifndef ROOT7_TCanvas
 #define ROOT7_TCanvas
 
+#include "ROOT/TDrawable.hxx"
+#include "ROOT/TypeTraits.hxx"
+#include "ROOT/TVirtualCanvasPainter.hxx"
+
 #include <experimental/string_view>
 #include <memory>
 #include <string>
 #include <vector>
 
-#include "ROOT/TDrawable.hxx"
-#include "ROOT/TypeTraits.hxx"
-#include "ROOT/TVirtualCanvasPainter.hxx"
-
 namespace ROOT {
 namespace Experimental {
 
@@ -139,7 +139,7 @@ public:
    void Update(bool async = false);
 
    /// Save canvas in image file
-   void SaveAs(const std::string &filename, bool async = false);
+   void SaveAs(const std::string &filename, bool async = false, CanvasCallback_t callback = nullptr);
 
    /// Get the canvas's title.
    const std::string &GetTitle() const { return fTitle; }

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

@@ -16,13 +16,16 @@
 #ifndef ROOT7_TVirtualCanvasPainter
 #define ROOT7_TVirtualCanvasPainter
 
-#include <memory>
-
 #include "ROOT/TDisplayItem.hxx"
 
+#include <memory>
+#include <functional>
+
 namespace ROOT {
 namespace Experimental {
 
+using CanvasCallback_t = std::function<void(bool)>;
+
 class TCanvas;
 
 namespace Internal {
@@ -60,7 +63,7 @@ public:
    virtual bool IsCanvasModified(uint64_t) const = 0;
 
    /// perform special action when drawing is ready
-   virtual void DoWhenReady(const std::string &, const std::string &, bool) = 0;
+   virtual void DoWhenReady(const std::string &, const std::string &, bool, CanvasCallback_t) = 0;
 
    virtual void NewDisplay(const std::string &where) = 0;
 

graf2d/gpad/v7/src/TCanvas.cxx

@@ -101,14 +101,14 @@ void ROOT::Experimental::TCanvas::Show(const std::string &where)
    }
 }
 
-void ROOT::Experimental::TCanvas::SaveAs(const std::string &filename, bool async)
+void ROOT::Experimental::TCanvas::SaveAs(const std::string &filename, bool async, CanvasCallback_t callback)
 {
    if (!fPainter)
       fPainter = Internal::TVirtualCanvasPainter::Create(*this, true);
    if (filename.find(".svg") != std::string::npos)
-      fPainter->DoWhenReady("SVG", filename, async);
+      fPainter->DoWhenReady("SVG", filename, async, callback);
    else if (filename.find(".png") != std::string::npos)
-      fPainter->DoWhenReady("PNG", filename, async);
+      fPainter->DoWhenReady("PNG", filename, async, callback);
 }
 
 // TODO: removal from GetHeldCanvases().

gui/canvaspainter/v7/src/TCanvasPainter.cxx

@@ -177,7 +177,8 @@ class TCanvasPainter : public THttpWSHandler,
       std::string fName;     ///<! command name
       std::string fArg;      ///<! command arg
       bool fRunning;         ///<! true when command submitted
-      WebCommand() : fId(), fName(), fArg(), fRunning(false) {}
+      ROOT::Experimental::CanvasCallback_t fCallback; ///<! callback function associated with command
+      WebCommand() : fId(), fName(), fArg(), fRunning(false), fCallback() {}
    };
 
    typedef std::list<WebConn> WebConnList;
@@ -248,7 +249,7 @@ class TCanvasPainter : public THttpWSHandler,
    virtual bool IsCanvasModified(uint64_t) const override;
 
    /// perform special action when drawing is ready
-   virtual void DoWhenReady(const std::string &cmd, const std::string &arg, bool async) final;
+   virtual void DoWhenReady(const std::string &cmd, const std::string &arg, bool async, ROOT::Experimental::CanvasCallback_t callback) final;
 
    // open new display for the canvas
    virtual void NewDisplay(const std::string &where) override;
@@ -430,7 +431,7 @@ bool TCanvasPainter::WaitWhenCanvasPainted(uint64_t ver)
    return false;
 }
 
-void TCanvasPainter::DoWhenReady(const std::string &name, const std::string &arg, bool async)
+void TCanvasPainter::DoWhenReady(const std::string &name, const std::string &arg, bool async, ROOT::Experimental::CanvasCallback_t callback)
 {
    if (!async && !fWaitingCmdId.empty()) {
       Error("DoWhenReady", "Fail to submit sync command when previous is still awaited - use async");
@@ -442,6 +443,7 @@ void TCanvasPainter::DoWhenReady(const std::string &name, const std::string &arg
    cmd.fName = name;
    cmd.fArg = arg;
    cmd.fRunning = false;
+   cmd.fCallback = callback;
    fCmds.push_back(cmd);
 
    if (!async) fWaitingCmdId = cmd.fId;
@@ -472,13 +474,15 @@ void TCanvasPainter::DoWhenReady(const std::string &name, const std::string &arg
 /// Remove front command from the command queue
 /// If necessary, configured call-back will be invoked
 
-void TCanvasPainter::PopFrontCommand(bool)
+void TCanvasPainter::PopFrontCommand(bool result)
 {
    if (fCmds.size() == 0) return;
 
    // simple condition, which will be checked in waiting loop
    if (!fWaitingCmdId.empty() && (fWaitingCmdId == fCmds.front().fId)) fWaitingCmdId.clear();
 
+   if (fCmds.front().fCallback) fCmds.front().fCallback(result);
+
    fCmds.pop_front();
 }
 

tutorials/v7/draw_v6.cxx

@@ -42,7 +42,11 @@ void draw_v6()
 
    canvas->Update(); // synchronous, wait until painting is finished
 
-   canvas->SaveAs("draw.png"); // asynchronous
+   // request to create PNG file in asynchronous mode and specify lambda function as callback
+   // when request processed by the client, callback called with result value
+   canvas->SaveAs("draw.png", true, [](bool res) { std::cout << "Producing PNG done res = " << (res ? "true" : "false") << std::endl; }); // asynchronous
 
+   // this function executed in synchronous mode (async = false is default),
+   // mean previous file saving will be completed as well at this point
    canvas->SaveAs("draw.svg"); // asynchronous
 }