Number renderers using consecutive digits in the sample

This has the disadvantage of not using the same accelerators in
different wxWidgets builds, but the advantage of appearing logical to a
casual user when running the sample, while having "0, 1, 3, 4" sequence
was surprising.

Alternatively, we could always add all menu items, but disable the ones
that are not available in the current build. It could be surprising to
see "GDI+" under non-MSW systems too though.

samples/drawing/drawing.cpp

@@ -2262,17 +2262,39 @@ MyFrame::MyFrame(const wxString& title, const wxPoint& pos, const wxSize& size)
 
     wxMenu *menuFile = new wxMenu;
 #if wxUSE_GRAPHICS_CONTEXT
-    m_menuItemUseDC = menuFile->AppendRadioItem(File_DC, "Use wx&DC\t0");
-    menuFile->AppendRadioItem(File_GC_Default, "Use default wx&GraphicContext\t1");
+    // Number the different renderer choices consecutively, starting from 0.
+    int accel = 0;
+    m_menuItemUseDC = menuFile->AppendRadioItem
+                      (
+                        File_DC,
+                        wxString::Format("Use wx&DC\t%d", accel++)
+                      );
+    menuFile->AppendRadioItem
+              (
+                File_GC_Default,
+                wxString::Format("Use default wx&GraphicContext\t%d", accel++)
+              );
 #if wxUSE_CAIRO
-    menuFile->AppendRadioItem(File_GC_Cairo, "Use &Cairo\t2");
+    menuFile->AppendRadioItem
+              (
+                File_GC_Cairo,
+                wxString::Format("Use &Cairo\t%d", accel++)
+              );
 #endif // wxUSE_CAIRO
 #ifdef __WXMSW__
 #if wxUSE_GRAPHICS_GDIPLUS
-    menuFile->AppendRadioItem(File_GC_GDIPlus, "Use &GDI+\t3");
+    menuFile->AppendRadioItem
+              (
+                File_GC_GDIPlus,
+                wxString::Format("Use &GDI+\t%d", accel++)
+              );
 #endif
 #if wxUSE_GRAPHICS_DIRECT2D
-    menuFile->AppendRadioItem(File_GC_Direct2D, "Use &Direct2D\t4");
+    menuFile->AppendRadioItem
+              (
+                File_GC_Direct2D,
+                wxString::Format("Use &Direct2D\t%d", accel++)
+              );
 #endif
 #endif // __WXMSW__
 #endif // wxUSE_GRAPHICS_CONTEXT