Merge branch 'gtk-dpi'

A bunch of improvements for per-monitor DPI support in wxGTK and
wxGraphicsContext more generally.

Closes https://github.com/wxWidgets/wxWidgets/pull/995

include/wx/display.h

@@ -49,6 +49,10 @@ public:
     // primary display and the only one which is always supported
     wxDisplay(unsigned n = 0);
 
+    // create display object corresponding to the display of the given window
+    // or the default one if the window display couldn't be found
+    explicit wxDisplay(const wxWindow* window);
+
     // dtor is not virtual as this is a concrete class not meant to be derived
     // from
 

include/wx/graphics.h

@@ -452,7 +452,7 @@ private:
 class WXDLLIMPEXP_CORE wxGraphicsContext : public wxGraphicsObject
 {
 public:
-    wxGraphicsContext(wxGraphicsRenderer* renderer);
+    wxGraphicsContext(wxGraphicsRenderer* renderer, wxWindow* window = NULL);
 
     virtual ~wxGraphicsContext();
 
@@ -490,6 +490,9 @@ public:
     // create a context that can be used for measuring texts only, no drawing allowed
     static wxGraphicsContext * Create();
 
+    // Return the window this context is associated with, if any.
+    wxWindow* GetWindow() const { return m_window; }
+
     // begin a new document (relevant only for printing / pdf etc) if there is a progress dialog, message will be shown
     virtual bool StartDoc( const wxString& message );
 
@@ -788,6 +791,12 @@ protected:
                                          wxDouble angle,
                                          const wxGraphicsBrush& backgroundBrush);
 
+private:
+    // The associated window, if any, i.e. if one was passed directly to
+    // Create() or the associated window of the wxDC this context was created
+    // from.
+    wxWindow* const m_window;
+
     wxDECLARE_NO_COPY_CLASS(wxGraphicsContext);
     wxDECLARE_ABSTRACT_CLASS(wxGraphicsContext);
 };

include/wx/private/display.h

@@ -81,8 +81,11 @@ public:
     // return the depth or 0 if unknown
     virtual int GetDepth() const = 0;
 
-    // return the resolution of the display, uses GetSizeMM() by default but
-    // can be also overridden directly
+    // return the scale factor used to convert logical pixels to physical ones
+    virtual double GetScaleFactor() const { return 1.0; }
+
+    // return the resolution of the display, uses GetSize(), GetScaleFactor()
+    // and GetSizeMM() by default but can be also overridden directly
     virtual wxSize GetPPI() const;
 
     // return the physical size of the display or (0, 0) if unknown: this is
@@ -115,6 +118,11 @@ protected:
     // create the object providing access to the display with the given index
     wxDisplayImpl(unsigned n) : m_index(n) { }
 
+    // Compute PPI from the sizes in pixels and mm.
+    //
+    // Return (0, 0) if physical size (in mm) is not known, i.e. 0.
+    static wxSize ComputePPI(int pxX, int pxY, int mmX, int mmY);
+
 
     // the index of this display (0 is always the primary one)
     const unsigned m_index;