Fix button widget when used with multiple viewports

vtkTexturedButtonRepresentation2D is a composite representation that
uses vtkBalloonRepresentation internally. The representation would need
to compensate the active viewport origin when deciding whether the
button was clicked.

Interaction/Widgets/vtkBalloonRepresentation.cxx

@@ -426,10 +426,21 @@ ComputeInteractionState(int X, int Y, int)
 {
   // Is it in the text region or the image region?
   double x0[3], x2[3];
+  int origin[2] = {0, 0};
+  if (this->Renderer)
+  {
+    origin[0] = (this->Renderer->GetOrigin())[0];
+    origin[1] = (this->Renderer->GetOrigin())[1];
+  }
   if ( this->ImageVisible )
   {
     this->TexturePoints->GetPoint(0,x0);
     this->TexturePoints->GetPoint(2,x2);
+    for (int i = 0; i < 2; ++i)
+    {
+      x0[i] += origin[i];
+      x2[i] += origin[i];
+    }
     if ( (x0[0] <= X && X <= x2[0]) && (x0[1] <= Y && Y <= x2[1]) )
     {
       return vtkBalloonRepresentation::OnImage;
@@ -440,6 +451,11 @@ ComputeInteractionState(int X, int Y, int)
   {
     this->FramePoints->GetPoint(0,x0);
     this->FramePoints->GetPoint(2,x2);
+    for (int i = 0; i < 2; ++i)
+    {
+      x0[i] += origin[i];
+      x2[i] += origin[i];
+    }
     if ( (x0[0] <= X && X <= x2[0]) && (x0[1] <= Y && Y <= x2[1]) )
     {
       return vtkBalloonRepresentation::OnText;

Interaction/Widgets/vtkButtonWidget.cxx

@@ -55,6 +55,29 @@ void vtkButtonWidget::CreateDefaultRepresentation()
   }
 }
 
+//----------------------------------------------------------------------
+void vtkButtonWidget::SetEnabled(int enabling)
+{
+  if ( enabling ) //----------------
+  {
+    if (this->Interactor)
+    {
+      if (!this->CurrentRenderer)
+      {
+        int X=this->Interactor->GetEventPosition()[0];
+        int Y=this->Interactor->GetEventPosition()[1];
+        this->SetCurrentRenderer(this->Interactor->FindPokedRenderer(X,Y));
+      }
+      this->CreateDefaultRepresentation();
+      this->WidgetRep->SetRenderer(this->CurrentRenderer);
+    }
+  }
+  else
+  {
+    this->SetCurrentRenderer(nullptr);
+  }
+  Superclass::SetEnabled(enabling);
+}
 
 //----------------------------------------------------------------------------------
 void vtkButtonWidget::MoveAction(vtkAbstractWidget *w)

Interaction/Widgets/vtkButtonWidget.h

@@ -96,6 +96,15 @@ public:
    */
   void CreateDefaultRepresentation() VTK_OVERRIDE;
 
+  /**
+   * The method for activating and deactivating this widget. This method
+   * must be overridden because it is a composite widget and does more than
+   * its superclasses' vtkAbstractWidget::SetEnabled() method. The
+   * method finds and sets the active viewport on the internal balloon
+   * representation.
+   */
+  void SetEnabled(int) VTK_OVERRIDE;
+
 protected:
   vtkButtonWidget();
   ~vtkButtonWidget() VTK_OVERRIDE {}

Interaction/Widgets/vtkTexturedButtonRepresentation2D.cxx

@@ -204,6 +204,7 @@ void vtkTexturedButtonRepresentation2D::PlaceWidget(double anchor[3], int size[2
 int vtkTexturedButtonRepresentation2D
 ::ComputeInteractionState(int X, int Y, int vtkNotUsed(modify))
 {
+  this->Balloon->SetRenderer(this->GetRenderer());
   if ( this->Balloon->ComputeInteractionState(X,Y) == vtkBalloonRepresentation::OnImage )
   {
     this->InteractionState = vtkButtonRepresentation::Inside;