Add default ctor to wxGLCanvas

It didn't make any sense to have Create() functions in this class
without the default ctor as they could be never used -- calling them
would result in creating the window twice.

Add the default ctor to make this class more similar to all the other
windows.

include/wx/gtk/glcanvas.h

@@ -29,6 +29,8 @@ class WXDLLIMPEXP_GL wxGLCanvas : public wxGLCanvasImpl
 {
     typedef wxGLCanvasImpl BaseType;
 public:
+    wxGLCanvas() = default;
+
     wxGLCanvas(wxWindow *parent,
                const wxGLAttributes& dispAttrs,
                wxWindowID id = wxID_ANY,

include/wx/msw/glcanvas.h

@@ -47,6 +47,8 @@ private:
 class WXDLLIMPEXP_GL wxGLCanvas : public wxGLCanvasBase
 {
 public:
+    wxGLCanvas() = default;
+
     explicit // avoid implicitly converting a wxWindow* to wxGLCanvas
     wxGLCanvas(wxWindow *parent,
                const wxGLAttributes& dispAttrs,
@@ -115,9 +117,6 @@ public:
 #endif // wxUSE_PALETTE
 
 protected:
-    // common part of all ctors
-    void Init();
-
     // the real window creation function, Create() may reuse it twice as we may
     // need to create an OpenGL window to query the available extensions and
     // then potentially delete and recreate it with another pixel format
@@ -133,7 +132,7 @@ protected:
 
 
     // HDC for this window, we keep it all the time
-    HDC m_hDC;
+    HDC m_hDC = nullptr;
 
 private:
     wxDECLARE_EVENT_TABLE();

include/wx/osx/glcanvas.h

@@ -60,6 +60,8 @@ private:
 class WXDLLIMPEXP_GL wxGLCanvas : public wxGLCanvasBase
 {
 public:
+    wxGLCanvas() = default;
+
     wxGLCanvas(wxWindow *parent,
                const wxGLAttributes& dispAttrs,
                wxWindowID id = wxID_ANY,
@@ -126,7 +128,7 @@ protected:
                               long style,
                   const wxString& name);
 
-    WXGLPixelFormat m_glFormat;
+    WXGLPixelFormat m_glFormat = nullptr;
     wxGLAttributes m_GLAttrs;
 
     wxDECLARE_EVENT_TABLE();

include/wx/qt/glcanvas.h

@@ -34,6 +34,8 @@ public:
 class WXDLLIMPEXP_GL wxGLCanvas : public wxGLCanvasBase
 {
 public:
+    wxGLCanvas() = default;
+
     explicit // avoid implicitly converting a wxWindow* to wxGLCanvas
     wxGLCanvas(wxWindow *parent,
                const wxGLAttributes& dispAttrs,

include/wx/x11/glcanvas.h

@@ -17,6 +17,8 @@
 class WXDLLIMPEXP_GL wxGLCanvas : public wxGLCanvasX11
 {
 public:
+    wxGLCanvas() = default;
+
     wxGLCanvas(wxWindow *parent,
                const wxGLAttributes& dispAttrs,
                wxWindowID id = wxID_ANY,

interface/wx/glcanvas.h

@@ -785,6 +785,15 @@ enum
 class wxGLCanvas : public wxWindow
 {
 public:
+    /**
+        Default constructor not creating the window.
+
+        Create() must be used to actually create it later.
+
+        @since 3.3.0
+     */
+    wxGLCanvas();
+
     /**
         Creates a window with the given parameters. Notice that you need to
         create and use a wxGLContext to output to this window.

src/msw/glcanvas.cpp

@@ -641,11 +641,6 @@ wxEND_EVENT_TABLE()
 // wxGLCanvas construction
 // ----------------------------------------------------------------------------
 
-void wxGLCanvas::Init()
-{
-    m_hDC = nullptr;
-}
-
 wxGLCanvas::wxGLCanvas(wxWindow *parent,
                        const wxGLAttributes& dispAttrs,
                        wxWindowID id,
@@ -655,8 +650,6 @@ wxGLCanvas::wxGLCanvas(wxWindow *parent,
                        const wxString& name,
                        const wxPalette& palette)
 {
-    Init();
-
     (void)Create(parent, dispAttrs, id, pos, size, style, name, palette);
 }
 
@@ -669,8 +662,6 @@ wxGLCanvas::wxGLCanvas(wxWindow *parent,
                        const wxString& name,
                        const wxPalette& palette)
 {
-    Init();
-
     (void)Create(parent, id, pos, size, style, name, attribList, palette);
 }
 

src/osx/glcanvas_osx.cpp

@@ -465,7 +465,6 @@ bool wxGLCanvas::Create(wxWindow *parent,
                         const wxString& name,
                         const wxPalette& WXUNUSED(palette))
 {
-    m_glFormat = nullptr;
     // Don't allow an empty list
     if ( !dispAttrs.GetGLAttrs() )
     {