Refactor wxGCDC to delegate acquiring/releasing HDC to wxGraphicsContext

Instead of implementing MSW-specific code to handle HDC for GDI+ context
directly in wxGCDC delegate acquiring/releasing HDC to underlying
wxGraphicsContext. Decoupling GDI+-specific code from wxGCDC will allow
us to implement handling HDC in other graphics renderers in a clean way.

include/wx/dcgraph.h

@@ -38,7 +38,7 @@ public:
 
 #ifdef __WXMSW__
     // override wxDC virtual functions to provide access to HDC associated with
-    // this Graphics object (implemented in src/msw/graphics.cpp)
+    // underlying wxGraphicsContext
     virtual WXHDC AcquireHDC() wxOVERRIDE;
     virtual void ReleaseHDC(WXHDC hdc) wxOVERRIDE;
 #endif // __WXMSW__

include/wx/graphics.h

@@ -881,6 +881,11 @@ public:
     void SetContentScaleFactor(double contentScaleFactor);
     double GetContentScaleFactor() const { return m_contentScaleFactor; }
 
+#ifdef __WXMSW__
+    virtual WXHDC GetNativeHDC() = 0;
+    virtual void ReleaseNativeHDC(WXHDC hdc) = 0;
+#endif
+
 protected:
     // These fields must be initialized in the derived class ctors.
     wxDouble m_width,

src/common/dcgraph.cpp

@@ -110,6 +110,25 @@ wxGCDC::~wxGCDC()
 {
 }
 
+#ifdef __WXMSW__
+WXHDC wxGCDC::AcquireHDC()
+{
+    wxGraphicsContext* const gc = GetGraphicsContext();
+    wxCHECK_MSG(gc, NULL, "can't acquire HDC because there is no wxGraphicsContext");
+    return gc->GetNativeHDC();
+}
+
+void wxGCDC::ReleaseHDC(WXHDC hdc)
+{
+    if ( !hdc )
+        return;
+
+    wxGraphicsContext* const gc = GetGraphicsContext();
+    wxCHECK_RET(gc, "can't release HDC because there is no wxGraphicsContext");
+    gc->ReleaseNativeHDC(hdc);
+}
+#endif // __WXMSW__
+
 wxIMPLEMENT_ABSTRACT_CLASS(wxGCDCImpl, wxDCImpl);
 
 wxGCDCImpl::wxGCDCImpl(wxDC *owner, wxGraphicsContext* context) :

src/generic/graphicc.cpp

@@ -512,6 +512,18 @@ public:
                                 wxDouble *descent, wxDouble *externalLeading ) const wxOVERRIDE;
     virtual void GetPartialTextExtents(const wxString& text, wxArrayDouble& widths) const wxOVERRIDE;
 
+#ifdef __WXMSW__
+    virtual WXHDC GetNativeHDC() wxOVERRIDE
+    {
+        wxFAIL_MSG("Can't get HDC from Cairo context");
+        return NULL;
+    };
+    virtual void ReleaseNativeHDC(WXHDC WXUNUSED(hdc)) wxOVERRIDE
+    {
+        wxFAIL_MSG("Can't release HDC for Cairo context");
+    };
+#endif
+
 protected:
     virtual void DoDrawText( const wxString &str, wxDouble x, wxDouble y ) wxOVERRIDE;
 

src/msw/graphics.cpp

@@ -483,6 +483,9 @@ public:
 
     Graphics* GetGraphics() const { return m_context; }
 
+    virtual WXHDC GetNativeHDC() wxOVERRIDE;
+    virtual void ReleaseNativeHDC(WXHDC hdc) wxOVERRIDE;
+
 protected:
     // Used from ctors (including those in the derived classes) and takes
     // ownership of the graphics pointer that must be non-NULL.
@@ -2506,6 +2509,17 @@ void wxGDIPlusContext::GetDPI(wxDouble* dpiX, wxDouble* dpiY) const
     }
 }
 
+WXHDC wxGDIPlusContext::GetNativeHDC()
+{
+    return m_context->GetHDC();
+}
+
+void wxGDIPlusContext::ReleaseNativeHDC(WXHDC hdc)
+{
+    if ( hdc )
+        m_context->ReleaseHDC((HDC)hdc);
+}
+
 //-----------------------------------------------------------------------------
 // wxGDIPlusPrintingContext implementation
 //-----------------------------------------------------------------------------
@@ -3003,39 +3017,4 @@ private:
 
 wxIMPLEMENT_DYNAMIC_CLASS(wxGDIPlusRendererModule, wxModule);
 
-// ----------------------------------------------------------------------------
-// wxMSW-specific parts of wxGCDC
-// ----------------------------------------------------------------------------
-
-WXHDC wxGCDC::AcquireHDC()
-{
-    wxGraphicsContext * const gc = GetGraphicsContext();
-    if ( !gc )
-        return NULL;
-
-    // we can't get the HDC if it is not a GDI+ context
-    wxCHECK_MSG(gc->GetRenderer() == wxGraphicsRenderer::GetGDIPlusRenderer(), NULL,
-                "can't get HDC because this is not GDI+ context");
-
-    Graphics * const g = static_cast<Graphics *>(gc->GetNativeContext());
-    return g ? g->GetHDC() : NULL;
-}
-
-void wxGCDC::ReleaseHDC(WXHDC hdc)
-{
-    if ( !hdc )
-        return;
-
-    wxGraphicsContext * const gc = GetGraphicsContext();
-    wxCHECK_RET( gc, "can't release HDC because there is no wxGraphicsContext" );
-
-    wxCHECK_RET(gc->GetRenderer() == wxGraphicsRenderer::GetGDIPlusRenderer(),
-                "can't release HDC because this is not GDI+ context");
-
-    Graphics * const g = static_cast<Graphics *>(gc->GetNativeContext());
-    wxCHECK_RET( g, "can't release HDC because there is no Graphics" );
-
-    g->ReleaseHDC((HDC)hdc);
-}
-
 #endif // wxUSE_GRAPHICS_GDIPLUS

src/msw/graphicsd2d.cpp

@@ -3836,6 +3836,8 @@ public:
     void PushState() wxOVERRIDE {}
     void PopState() wxOVERRIDE {}
     void Flush() wxOVERRIDE {}
+    WXHDC GetNativeHDC() wxOVERRIDE { return NULL; };
+    void ReleaseNativeHDC(WXHDC WXUNUSED(hdc)) wxOVERRIDE {};
 
 protected:
     void DoDrawText(const wxString&, wxDouble, wxDouble) wxOVERRIDE {}
@@ -3992,6 +3994,16 @@ public:
         return GetRenderTarget();
     }
 
+    WXHDC GetNativeHDC() wxOVERRIDE
+    {
+        wxFAIL_MSG("Can't get HDC from Direct2D context");
+        return NULL;
+    };
+    void ReleaseNativeHDC(WXHDC WXUNUSED(hdc)) wxOVERRIDE
+    {
+        wxFAIL_MSG("Can't release HDC for Direct2D context");
+    };
+
 private:
     void Init();