Add GetOpenGLScaleFactor() to abstract OpenGL coordinates scaling

The fix for OpenGL coordinates when using high DPI in b134589cbb (Fix
OpenGL samples when using HiDPI displays, 2019-08-06) did fix it for GTK
3 and macOS, but broke it for MSW and other platforms not using pixel
scaling, as window coordinates are the same as OpenGL ones there, while
GetContentScaleFactor() can still return values > 1 even on these
platforms.

Provide new GetOpenGLScaleFactor() function abstracting this platform
difference and use it in all OpenGL samples to make them work correctly
in high DPI under all platforms.

Closes https://github.com/wxWidgets/wxWidgets/pull/1944

Closes #17391.

docs/changes.txt

@@ -83,7 +83,7 @@ Changes in behaviour not resulting in compilation errors
 
 - wxGLCanvas now uses physical pixels on high DPI displays under platforms
   where they're different from logical ones (wxGTK3, wxOSX). Multiply logical
-  coordinates, e.g. returned by wxWindow::GetSize() by GetContentScaleFactor()
+  coordinates, e.g. returned by wxWindow::GetSize() by GetOpenGLScaleFactor()
   before using them with OpenGL functions.
 
 - wxGTK now uses wxID_NONE item ID for wxEVT_MENU_HIGHLIGHT events sent when

include/wx/glcanvas.h

@@ -258,6 +258,11 @@ public:
     // as a parameter
     wxGLContextAttrs& GetGLCTXAttrs() { return m_GLCTXAttrs; }
 
+    // Return the factor to apply to transform window coordinates (e.g. sizes)
+    // to OpenGL coordinates: it can be different from 1 on the platforms where
+    // logical pixels are different from physical ones (i.e. wxGTK3 and wxOSX).
+    virtual double GetOpenGLScaleFactor() const;
+
     // deprecated methods using the implicit wxGLContext
 #if WXWIN_COMPATIBILITY_2_8
     wxDEPRECATED( wxGLContext* GetContext() const );

include/wx/gtk/glcanvas.h

@@ -60,6 +60,8 @@ public:
 
     virtual bool SetBackgroundStyle(wxBackgroundStyle style) wxOVERRIDE;
 
+    virtual double GetOpenGLScaleFactor() const wxOVERRIDE;
+
     // implement wxGLCanvasX11 methods
     // --------------------------------
 

include/wx/osx/glcanvas.h

@@ -100,7 +100,7 @@ public:
 
     // implement wxGLCanvasBase methods
     virtual bool SwapBuffers() wxOVERRIDE;
-
+    virtual double GetOpenGLScaleFactor() const wxOVERRIDE;
 
     // Mac-specific functions
     // ----------------------

interface/wx/glcanvas.h

@@ -752,7 +752,7 @@ enum
     platforms where wxWindow uses logical pixels, affected by the coordinate
     scaling, on high DPI displays. Thus, if you want to set the OpenGL view
     port to the size of entire window, you must multiply the result returned by
-    wxWindow::GetClientSize() by wxWindow::GetContentScaleFactor() before
+    wxWindow::GetClientSize() by wxGLCanvas::GetOpenGLScaleFactor() before
     passing it to @c glViewport(). Same considerations apply to other OpenGL
     functions and other coordinates, notably those retrieved from wxMouseEvent
     in the event handlers.
@@ -936,6 +936,23 @@ public:
     */
     bool SetCurrent(const wxGLContext& context) const;
 
+    /**
+        Returns the scale factor for transformation between logical and
+        physical OpenGL coordinates.
+
+        This factor is always 1 on the platforms where logical pixels are the
+        same as physical ones, in any DPI (such as MSW), but can be different
+        from it on the platforms where logical and physical pixels may differ
+        due to DPI scaling (such as GTK 3 or macOS).
+
+        To handle the differences between the platforms, always multiply the
+        values expressed in window coordinates (window sizes, mouse position
+        etc) by this factor before passing them to OpenGL functions.
+
+        @since 3.1.4
+    */
+    double GetOpenGLScaleFactor() const;
+
     /**
         Swaps the double-buffer of this window, making the back-buffer the
         front-buffer and vice versa, so that the output of the previous OpenGL

samples/opengl/cube/cube.cpp

@@ -349,7 +349,7 @@ void TestGLCanvas::OnPaint(wxPaintEvent& WXUNUSED(event))
     // multiple canvases: If we updated the viewport in the wxSizeEvent
     // handler, changing the size of one canvas causes a viewport setting that
     // is wrong when next another canvas is repainted.
-    const wxSize ClientSize = GetClientSize() * GetContentScaleFactor();
+    const wxSize ClientSize = GetClientSize() * GetOpenGLScaleFactor();
 
     TestGLContext& canvas = wxGetApp().GetContext(this, m_useStereo);
     glViewport(0, 0, ClientSize.x, ClientSize.y);

samples/opengl/isosurf/isosurf.cpp

@@ -280,7 +280,7 @@ void TestGLCanvas::OnSize(wxSizeEvent& event)
     // This is OK here only because there is only one canvas that uses the
     // context. See the cube sample for that case that multiple canvases are
     // made current with one context.
-    const wxSize size = event.GetSize() * GetContentScaleFactor();
+    const wxSize size = event.GetSize() * GetOpenGLScaleFactor();
     glViewport(0, 0, size.x, size.y);
 }
 

samples/opengl/penguin/penguin.cpp

@@ -306,7 +306,7 @@ void TestGLCanvas::ResetProjectionMode()
     // or more than one wxGLContext in the application.
     SetCurrent(*m_glRC);
 
-    const wxSize ClientSize = GetClientSize() * GetContentScaleFactor();
+    const wxSize ClientSize = GetClientSize() * GetOpenGLScaleFactor();
 
     // It's up to the application code to update the OpenGL viewport settings.
     // In order to avoid extensive context switching, consider doing this in

samples/opengl/pyramid/pyramid.cpp

@@ -565,7 +565,7 @@ void MyGLCanvas::OnSize(wxSizeEvent& event)
     SetCurrent(*m_oglContext);
 
     // It's up to the application code to update the OpenGL viewport settings.
-    const wxSize size = event.GetSize() * GetContentScaleFactor();
+    const wxSize size = event.GetSize() * GetOpenGLScaleFactor();
     m_winHeight = size.y;
     m_oglManager->SetViewport(0, 0, size.x, m_winHeight);
 

src/common/glcmn.cpp

@@ -376,6 +376,11 @@ bool wxGLCanvasBase::ParseAttribList(const int *attribList,
     return true;
 }
 
+double wxGLCanvasBase::GetOpenGLScaleFactor() const
+{
+    return 1.0;
+}
+
 // ============================================================================
 // compatibility layer for OpenGL 3 and OpenGL ES
 // ============================================================================

src/gtk/glcanvas.cpp

@@ -271,4 +271,13 @@ void wxGLCanvas::GTKInitImplicitContext()
 
 #endif // WXWIN_COMPATIBILITY_2_8
 
+double wxGLCanvas::GetOpenGLScaleFactor() const
+{
+#ifdef __WXGTK3__
+    return GetContentScaleFactor();
+#else
+    return 1.0;
+#endif
+}
+
 #endif // wxUSE_GLCANVAS

src/osx/glcanvas_osx.cpp

@@ -562,6 +562,11 @@ bool wxGLCanvas::IsAGLMultiSampleAvailable()
     return s_isMultiSampleAvailable != 0;
 }
 
+double wxGLCanvas::GetOpenGLScaleFactor() const
+{
+    return GetContentScaleFactor();
+}
+
 /* static */
 bool wxGLCanvasBase::IsDisplaySupported(const wxGLAttributes& dispAttrs)
 {