Improve wxQt OpenGL canvas implementation:

- Support wxGLContext::SetCurrent.
- Pass GL canvas attributes via ParseAttribList to handle defaults.
- Remove OpenGL not implemented message.
- Prevent QGLWidget from changing OpenGL state before we paint.
- Set Qt::StrongFocus for wxQtGLWidget to allow keyboard input.
- Use QtCanPaintWithoutActivePainter to fix wxPaintDCImpl assert when using wxGLCanvas.

include/wx/qt/glcanvas.h

@@ -24,6 +24,9 @@ public:
 
     virtual bool SetCurrent(const wxGLCanvas& win) const override;
 
+private:
+    QGLContext* m_glContext = nullptr;
+
     wxDECLARE_CLASS(wxGLContext);
 };
 
@@ -78,7 +81,9 @@ public:
 
     virtual bool SwapBuffers() override;
 
-    static bool ConvertWXAttrsToQtGL(const int *wxattrs, QGLFormat &format);
+    virtual bool QtCanPaintWithoutActivePainter() const override;
+
+    static bool ConvertWXAttrsToQtGL(const wxGLAttributes &glattrs, const wxGLContextAttrs ctxAttrs, QGLFormat &format);
 
 private:
     wxDECLARE_CLASS(wxGLCanvas);

include/wx/qt/window.h

@@ -151,6 +151,7 @@ public:
     void QtSetPicture( QPicture* pict );
 
     QPainter *QtGetPainter();
+    virtual bool QtCanPaintWithoutActivePainter() const;
 
     virtual bool QtHandlePaintEvent  ( QWidget *handler, QPaintEvent *event );
     virtual bool QtHandleResizeEvent ( QWidget *handler, QResizeEvent *event );