Add wxDC::GetFontMetrics() and implement it for wxMSW.

Add a new wxDC method allowing to retrieve the font characteristics not
available from GetTextExtent(), notably the internal leading (and also the
average font width).

Currently this is implemented for wxMSW only, the internal leading is always 0
in the other ports.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67063 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/dc.h

@@ -114,6 +114,27 @@ enum wxMappingMode
     wxMM_POINTS
 };
 
+// Description of text characteristics.
+struct wxFontMetrics
+{
+    wxFontMetrics()
+    {
+        height =
+        ascent =
+        descent =
+        internalLeading =
+        externalLeading =
+        averageWidth = 0;
+    }
+
+    int height,             // Total character height.
+        ascent,             // Part of the height above the baseline.
+        descent,            // Part of the height below the baseline.
+        internalLeading,    // Intra-line spacing.
+        externalLeading,    // Inter-line spacing.
+        averageWidth;       // Average font width, a.k.a. "x-width".
+};
+
 #if WXWIN_COMPATIBILITY_2_8
 
 //-----------------------------------------------------------------------------
@@ -375,6 +396,18 @@ public:
 
     virtual wxCoord GetCharHeight() const = 0;
     virtual wxCoord GetCharWidth() const = 0;
+
+    // The derived classes should really override DoGetFontMetrics() to return
+    // the correct values in the future but for now provide a default
+    // implementation in terms of DoGetTextExtent() to avoid breaking the
+    // compilation of all other ports as wxMSW is the only one to implement it.
+    virtual void DoGetFontMetrics(int *height,
+                                  int *ascent,
+                                  int *descent,
+                                  int *internalLeading,
+                                  int *externalLeading,
+                                  int *averageWidth) const;
+
     virtual void DoGetTextExtent(const wxString& string,
                                  wxCoord *x, wxCoord *y,
                                  wxCoord *descent = NULL,
@@ -840,6 +873,15 @@ public:
     wxCoord GetCharWidth() const
         { return m_pimpl->GetCharWidth(); }
 
+    wxFontMetrics GetFontMetrics() const
+    {
+        wxFontMetrics fm;
+        m_pimpl->DoGetFontMetrics(&fm.height, &fm.ascent, &fm.descent,
+                                  &fm.internalLeading, &fm.externalLeading,
+                                  &fm.averageWidth);
+        return fm;
+    }
+
     void GetTextExtent(const wxString& string,
                        wxCoord *x, wxCoord *y,
                        wxCoord *descent = NULL,