ScreenshotCommand uses hooks in AudacityCommand and Effect dialogs...

... so that they don't have a static linkage dependency on it, and that frees
it from dependency cycles, to a high level

src/commands/AudacityCommand.cpp

@@ -44,10 +44,27 @@ ShuttleGui.
 #include "../widgets/HelpSystem.h"
 #include "../widgets/ErrorDialog.h"
 
-#include "../commands/ScreenshotCommand.h"
-
 #include <unordered_map>
 
+namespace {
+
+AudacityCommand::VetoDialogHook &GetVetoDialogHook()
+{
+   static AudacityCommand::VetoDialogHook sHook = nullptr;
+   return sHook;
+}
+
+}
+
+auto AudacityCommand::SetVetoDialogHook( VetoDialogHook hook )
+   -> VetoDialogHook
+{
+   auto &theHook = GetVetoDialogHook();
+   auto result = theHook;
+   theHook = hook;
+   return result;
+}
+
 AudacityCommand::AudacityCommand()
 {
    mProgress = NULL;
@@ -105,7 +122,8 @@ bool AudacityCommand::ShowInterface(wxWindow *parent, bool WXUNUSED(forceModal))
    mUIDialog->SetMinSize(mUIDialog->GetSize());
 
    // The Screenshot command might be popping this dialog up, just to capture it.
-   if( ScreenshotCommand::MayCapture( mUIDialog ) )
+   auto hook = GetVetoDialogHook();
+   if( hook && hook( mUIDialog ) )
       return false;
 
    bool res = mUIDialog->ShowModal() != 0;

src/commands/AudacityCommand.h

@@ -45,6 +45,11 @@ class AUDACITY_DLL_API AudacityCommand /* not final */ : public wxEvtHandler,
  public:
    AudacityCommand();
    virtual ~AudacityCommand();
+   
+   // Type of a registered function that, if it returns true,
+   // causes ShowInterface to return early without making any dialog
+   using VetoDialogHook = bool (*) ( wxDialog* );
+   static VetoDialogHook SetVetoDialogHook( VetoDialogHook hook );
 
    // ComponentInterface implementation
 

src/commands/ScreenshotCommand.cpp

@@ -20,6 +20,8 @@ small calculations of rectangles.
 #include "../Audacity.h"
 #include "ScreenshotCommand.h"
 
+#include <mutex>
+
 #include "../Project.h"
 #include <wx/toplevel.h>
 #include <wx/dcscreen.h>
@@ -31,6 +33,7 @@ small calculations of rectangles.
 
 #include "../AdornedRulerPanel.h"
 #include "../TrackPanel.h"
+#include "../effects/Effect.h"
 #include "../toolbars/ToolManager.h"
 #include "../Prefs.h"
 #include "../Shuttle.h"
@@ -87,7 +90,19 @@ kBackgroundStrings[ ScreenshotCommand::nBackgrounds ] =
 };
 
 
-bool ScreenshotCommand::DefineParams( ShuttleParams & S ){ 
+ScreenshotCommand::ScreenshotCommand()
+{
+   mbBringToTop=true;
+   mIgnore=NULL;
+   
+   static std::once_flag flag;
+   std::call_once( flag, []{
+      AudacityCommand::SetVetoDialogHook( MayCapture );
+      Effect::SetVetoDialogHook( MayCapture );
+   });
+}
+
+bool ScreenshotCommand::DefineParams( ShuttleParams & S ){
    S.Define(                               mPath,        wxT("Path"),         wxT(""));
    S.DefineEnum(                           mWhat,        wxT("CaptureWhat"),  kwindow,kCaptureWhatStrings, nCaptureWhats );
    S.DefineEnum(                           mBack,        wxT("Background"),   kNone, kBackgroundStrings, nBackgrounds );

src/commands/ScreenshotCommand.h

@@ -78,7 +78,7 @@ public:
       nCaptureWhats
    };
 
-   ScreenshotCommand(){ mbBringToTop=true;mIgnore=NULL;};
+   ScreenshotCommand();
    // ComponentInterface overrides
    ComponentInterfaceSymbol GetSymbol() override {return SCREENSHOT_PLUGIN_SYMBOL;};
    wxString GetDescription() override {return _("Takes screenshots.");};