added initial version of the Doxygen manual

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@51901 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/doxygen/overviews/dc.h

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+/////////////////////////////////////////////////////////////////////////////
+// Name:        dc
+// Purpose:     topic overview
+// Author:      wxWidgets team
+// RCS-ID:      $Id$
+// Licence:     wxWindows license
+/////////////////////////////////////////////////////////////////////////////
+
+/*!
+ 
+ @page dc_overview Device context overview
+ 
+ Classes: #wxBufferedDC, #wxBufferedPaintDC, #wxDC, #wxPostScriptDC,
+ #wxMetafileDC, #wxMemoryDC, #wxPrinterDC,
+ #wxScreenDC, #wxClientDC, #wxPaintDC,
+ #wxWindowDC.
+ A wxDC is a @e device context onto which graphics and text can be drawn.
+ The device context is intended to represent a number of output devices in a generic way,
+ with the same API being used throughout.
+ Some device contexts are created temporarily in order to draw on a window.
+ This is @true of #wxScreenDC, #wxClientDC, #wxPaintDC,
+ and #wxWindowDC. The following describes the differences between
+ these device contexts and when you should use them.
+ 
+ 
+  @b wxScreenDC. Use this to paint on the screen, as opposed to an individual window.
+  @b wxClientDC. Use this to paint on the client area of window (the part without
+ borders and other decorations), but do not use it from within an #wxPaintEvent.
+  @b wxPaintDC. Use this to paint on the client area of a window, but @e only from
+ within a #wxPaintEvent.
+  @b wxWindowDC. Use this to paint on the whole area of a window, including decorations.
+ This may not be available on non-Windows platforms.
+ 
+ 
+ To use a client, paint or window device context, create an object on the stack with
+ the window as argument, for example:
+ 
+ @code
+ void MyWindow::OnMyCmd(wxCommandEvent& event)
+   {
+     wxClientDC dc(window);
+     DrawMyPicture(dc);
+   }
+ @endcode
+ 
+ Try to write code so it is parameterised by wxDC - if you do this, the same piece of code may
+ write to a number of different devices, by passing a different device context. This doesn't
+ work for everything (for example not all device contexts support bitmap drawing) but
+ will work most of the time.
+ 
+ */
+ 
+