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by Daniel T Chen
Import Debian 2.6.3.2.1 |
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\section{Device context overview}\label{dcoverview} |
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Classes: \helpref{wxBufferedDC}{wxbuffereddc}, \helpref{wxBufferedPaintDC}{wxbufferedpaintdc}, \helpref{wxDC}{wxdc}, \helpref{wxPostScriptDC}{wxpostscriptdc},\rtfsp |
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\rtfsp\helpref{wxMetafileDC}{wxmetafiledc}, \helpref{wxMemoryDC}{wxmemorydc}, \helpref{wxPrinterDC}{wxprinterdc},\rtfsp |
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\helpref{wxScreenDC}{wxscreendc}, \helpref{wxClientDC}{wxclientdc}, \helpref{wxPaintDC}{wxpaintdc},\rtfsp |
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\helpref{wxWindowDC}{wxwindowdc}. |
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A wxDC is a {\it device context} onto which graphics and text can be drawn. |
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The device context is intended to represent a number of output devices in a generic way, |
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with the same API being used throughout. |
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Some device contexts are created temporarily in order to draw on a window. |
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This is true of \helpref{wxScreenDC}{wxscreendc}, \helpref{wxClientDC}{wxclientdc}, \helpref{wxPaintDC}{wxpaintdc}, |
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and \helpref{wxWindowDC}{wxwindowdc}. The following describes the differences between |
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these device contexts and when you should use them. |
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\begin{itemize}\itemsep=0pt |
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\item {\bf wxScreenDC.} Use this to paint on the screen, as opposed to an individual window. |
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\item {\bf wxClientDC.} Use this to paint on the client area of window (the part without |
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borders and other decorations), but do not use it from within an \helpref{wxPaintEvent}{wxpaintevent}. |
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\item {\bf wxPaintDC.} Use this to paint on the client area of a window, but {\it only} from |
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within a \helpref{wxPaintEvent}{wxpaintevent}. |
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\item {\bf wxWindowDC.} Use this to paint on the whole area of a window, including decorations. |
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This may not be available on non-Windows platforms. |
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\end{itemize} |
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To use a client, paint or window device context, create an object on the stack with |
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the window as argument, for example: |
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\begin{verbatim} |
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void MyWindow::OnMyCmd(wxCommandEvent& event)
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{
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wxClientDC dc(window); |
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DrawMyPicture(dc); |
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}
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\end{verbatim} |
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Try to write code so it is parameterised by wxDC - if you do this, the same piece of code may |
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write to a number of different devices, by passing a different device context. This doesn't |
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work for everything (for example not all device contexts support bitmap drawing) but |
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will work most of the time. |
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