added GetIfActive() method returning non-NULL engine only if themes are not only available, but really use

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@30630 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/uxtheme.h

@@ -261,6 +261,10 @@ public:
     // get the theme engine or NULL if themes are not available
     static wxUxThemeEngine *Get();
 
+    // get the theme enging or NULL if themes are not available or not used for
+    // this application
+    static wxUxThemeEngine *GetIfActive();
+
     // all uxtheme.dll functions
     wxUX_THEME_DECLARE(PFNWXUOPENTHEMEDATA, OpenThemeData)
     wxUX_THEME_DECLARE(PFNWXUCLOSETHEMEDATA, CloseThemeData)
@@ -343,6 +347,14 @@ private:
     DECLARE_NO_COPY_CLASS(wxUxThemeEngine)
 };
 
+/* static */ inline wxUxThemeEngine *wxUxThemeEngine::GetIfActive()
+{
+    wxUxThemeEngine *engine = Get();
+    return engine && engine->IsAppThemed() && engine->IsThemeActive()
+                ? engine
+                : NULL;
+}
+
 #if !wxUSE_UXTHEME
 
 /* static */ inline wxUxThemeEngine *wxUxThemeEngine::Get()
@@ -350,6 +362,11 @@ private:
     return NULL;
 }
 
+/* static */ inline wxUxThemeEngine *wxUxThemeEngine::GetIfActive()
+{
+    return NULL;
+}
+
 #endif // !wxUSE_UXTHEME
 
 // ----------------------------------------------------------------------------