docs/latex/wx/tdc.tex

   1 \section{Device context overview}\label{dcoverview}
   2
   3 Classes: \helpref{wxDC}{wxdc}, \helpref{wxPostScriptDC}{wxpostscriptdc},\rtfsp
   4 \rtfsp\helpref{wxMetafileDC}{wxmetafiledc}, \helpref{wxMemoryDC}{wxmemorydc}, \helpref{wxPrinterDC}{wxprinterdc},\rtfsp
   5 \helpref{wxScreenDC}{wxscreendc}, \helpref{wxClientDC}{wxclientdc}, \helpref{wxPaintDC}{wxpaintdc},\rtfsp
   6 \helpref{wxWindowDC}{wxwindowdc}.
   7
   8 A wxDC is a {\it device context} onto which graphics and text can be drawn.
   9 The device context is intended to represent a number of output devices in a generic way,
  10 with the same API being used throughout.
  11
  12 Some device contexts are created temporarily in order to draw on a window.
  13 This is true of \helpref{wxScreenDC}{wxscreendc}, \helpref{wxClientDC}{wxclientdc}, \helpref{wxPaintDC}{wxpaintdc},
  14 and \helpref{wxWindowDC}{wxwindowdc}. The following describes the differences between
  15 these device contexts and when you should use them.
  16
  17 \begin{itemize}\itemsep=0pt
  18 \item {\bf wxScreenDC.} Use this to paint on the screen, as opposed to an individual window.
  19 \item {\bf wxClientDC.} Use this to paint on the client area of window (the part without
  20 borders and other decorations), but do not use it from within an \helpref{wxPaintEvent}{wxpaintevent}.
  21 \item {\bf wxPaintDC.} Use this to paint on the client area of a window, but {\it only} from
  22 within a \helpref{wxPaintEvent}{wxpaintevent}.
  23 \item {\bf wxWindowDC.} Use this to paint on the whole area of a window, including decorations.
  24 This may not be available on non-Windows platforms.
  25 \end{itemize}
  26
  27 To use a client, paint or window device context, create an object on the stack with
  28 the window as argument, for example:
  29
  30 \begin{verbatim}
  31   void MyWindow::OnMyCmd(wxCommandEvent& event)
  32   {
  33     wxClientDC dc(window);
  34     DrawMyPicture(dc);
  35   }
  36 \end{verbatim}
  37
  38 Try to write code so it is parameterised by wxDC - if you do this, the same piece of code may
  39 write to a number of different devices, by passing a different device context. This doesn't
  40 work for everything (for example not all device contexts support bitmap drawing) but
  41 will work most of the time.
  42