Extend TCanvasImp interface

- let create TVirtualPadPainter via the TCanvasImp.
- handling of TCanvas::Update() can be perfromed in TCanvasImp

core/base/inc/TCanvasImp.h

@@ -25,7 +25,7 @@
 #include "Rtypes.h"
 
 class TCanvas;
-
+class TVirtualPadPainter;
 
 class TCanvasImp {
 friend class TCanvas;
@@ -42,6 +42,9 @@ friend class TCanvas;
    virtual void   Unlock() { }
    virtual Bool_t IsLocked() { return kFALSE; }
 
+   virtual Bool_t PerformUpdate() { return kFALSE; }
+   virtual TVirtualPadPainter *CreatePadPainter() { return 0; }
+
 public:
    TCanvasImp(TCanvas *c=0) : fCanvas(c) { }
    TCanvasImp(TCanvas *c, const char *name, UInt_t width, UInt_t height);

graf2d/gpad/src/TCanvas.cxx

@@ -2249,14 +2249,18 @@ void TCanvas::Update()
 
    fUpdating = kTRUE;
 
-   if (!IsBatch()) FeedbackMode(kFALSE);      // Goto double buffer mode
+   if (!fCanvasImp->PerformUpdate()) {
 
-   if (!UseGL())
-      PaintModified();           // Repaint all modified pad's
+      if (!IsBatch()) FeedbackMode(kFALSE);      // Goto double buffer mode
 
-   Flush();                   // Copy all pad pixmaps to the screen
+      if (!UseGL())
+         PaintModified();           // Repaint all modified pad's
+
+      Flush();                   // Copy all pad pixmaps to the screen
+
+      SetCursor(kCross);
+   }
 
-   SetCursor(kCross);
    fUpdating = kFALSE;
 }
 
@@ -2299,9 +2303,10 @@ void TCanvas::CreatePainter()
 {
    //Even for batch mode painter is still required, just to delegate
    //some calls to batch "virtual X".
-   if (!UseGL() || fBatch)
-      fPainter = new TPadPainter;//Do not need plugin manager for this!
-   else {
+   if (!UseGL() || fBatch) {
+      fPainter = !fCanvasImp ? 0 : fCanvasImp->CreatePadPainter();
+      if (!fPainter) fPainter = new TPadPainter;//Do not need plugin manager for this!
+   } else {
       fPainter = TVirtualPadPainter::PadPainter("gl");
       if (!fPainter) {
          Error("CreatePainter", "GL Painter creation failed! Will use default!");