Add wxDisplay::GetPPI() to use instead of wxGetDisplayPPI()

While this is not done for all the ports yet, the new API allows
returning different PPI values for different monitors, unlike the old
(and still existing, but implemented in terms of the new one) global
function.

include/wx/display.h

@@ -11,6 +11,7 @@
 #define _WX_DISPLAY_H_BASE_
 
 #include "wx/defs.h"
+#include "wx/gdicmn.h"      // wxSize
 
 // NB: no #if wxUSE_DISPLAY here, the display geometry part of this class (but
 //     not the video mode stuff) is always available but if wxUSE_DISPLAY == 0
@@ -77,6 +78,9 @@ public:
     // get the depth, i.e. number of bits per pixel (0 if unknown)
     int GetDepth() const;
 
+    // get the resolution of this monitor in pixels per inch
+    wxSize GetPPI() const;
+
     // name may be empty
     wxString GetName() const;
 

include/wx/gdicmn.h

@@ -1080,6 +1080,9 @@ extern WXDLLIMPEXP_DATA_CORE(const wxPoint) wxDefaultPosition;
 extern void WXDLLIMPEXP_CORE wxInitializeStockLists();
 extern void WXDLLIMPEXP_CORE wxDeleteStockLists();
 
+// Note: all the display-related functions here exist for compatibility only,
+// please use wxDisplay class in the new code
+
 // is the display colour (or monochrome)?
 extern bool WXDLLIMPEXP_CORE wxColourDisplay();
 

include/wx/private/display.h

@@ -81,6 +81,15 @@ 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
+    virtual wxSize GetPPI() const;
+
+    // return the physical size of the display or (0, 0) if unknown: this is
+    // only used by GetPPI() implementation in the base class, so if GetPPI()
+    // is overridden, this one doesn't have to be implemented
+    virtual wxSize GetSizeMM() const { return wxSize(0, 0); }
+
     // return the name (may be empty)
     virtual wxString GetName() const { return wxString(); }