9b50920f5e
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@42795 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
97 lines
3.2 KiB
TeX
97 lines
3.2 KiB
TeX
\section{\class{wxMemoryDC}}\label{wxmemorydc}
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A memory device context provides a means to draw graphics onto a bitmap. When
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drawing in to a mono-bitmap, using {\tt wxWHITE}, {\tt wxWHITE\_PEN} and
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{\tt wxWHITE\_BRUSH}
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will draw the background colour (i.e. 0) whereas all other colours will draw the
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foreground colour (i.e. 1).
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\wxheading{Derived from}
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\helpref{wxDC}{wxdc}\\
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\helpref{wxObject}{wxobject}
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\wxheading{Include files}
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<wx/dcmemory.h>
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\wxheading{Remarks}
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A bitmap must be selected into the new memory DC before it may be used
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for anything. Typical usage is as follows:
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\begin{verbatim}
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// Create a memory DC
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wxMemoryDC temp_dc;
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temp_dc.SelectObject(test_bitmap);
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// We can now draw into the memory DC...
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// Copy from this DC to another DC.
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old_dc.Blit(250, 50, BITMAP_WIDTH, BITMAP_HEIGHT, temp_dc, 0, 0);
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\end{verbatim}
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Note that the memory DC {\it must} be deleted (or the bitmap selected out of it) before a bitmap
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can be reselected into another memory DC.
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\wxheading{See also}
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\helpref{wxBitmap}{wxbitmap}, \helpref{wxDC}{wxdc}
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\latexignore{\rtfignore{\wxheading{Members}}}
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\membersection{wxMemoryDC::wxMemoryDC}\label{wxmemorydcctor}
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\func{}{wxMemoryDC}{\void}
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Constructs a new memory device context.
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Use the \helpref{IsOk}{wxdcisok} member to test whether the constructor was successful
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in creating a usable device context.
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Don't forget to select a bitmap into the DC before drawing on it.
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\func{}{wxMemoryDC}{\param{wxBitmap\& }{bitmap}}
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Constructs a new memory device context and calls \helpref{SelectObject}{wxmemorydcselectobject}
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with the given bitmap.
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Use the \helpref{IsOk}{wxdcisok} member to test whether the constructor was successful
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in creating a usable device context.
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\membersection{wxMemoryDC::SelectObject}\label{wxmemorydcselectobject}
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\func{void}{SelectObject}{\param{wxBitmap\& }{bitmap}}
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Works exactly like \helpref{SelectObjectAsSource}{wxmemorydcselectobjectassource} but
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this is the function you should use when you select a bitmap because you want to modify
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it, e.g. drawing on this DC.
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Be careful to use this function and not \helpref{SelectObjectAsSource}{wxmemorydcselectobjectassource}
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when you want to modify the bitmap you are selecting otherwise you may incurr in some
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problems related to wxBitmap being a reference counted object
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(see \helpref{reference counting overview}{trefcount}).
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\wxheading{See also}
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\helpref{wxDC::DrawBitmap}{wxdcdrawbitmap}
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\membersection{wxMemoryDC::SelectObjectAsSource}\label{wxmemorydcselectobjectassource}
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\func{void}{SelectObjectAsSource}{\param{const wxBitmap\& }{bitmap}}
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Selects the given bitmap into the device context, to use as the memory
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bitmap. Selecting the bitmap into a memory DC allows you to draw into
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the DC (and therefore the bitmap) and also to use \helpref{wxDC::Blit}{wxdcblit} to copy
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the bitmap to a window. For this purpose, you may find \helpref{wxDC::DrawIcon}{wxdcdrawicon}\rtfsp
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easier to use instead.
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If the argument is wxNullBitmap (or some other uninitialised wxBitmap) the current bitmap is
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selected out of the device context, and the original bitmap restored, allowing the current bitmap to
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be destroyed safely.
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\wxheading{See also}
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\helpref{wxMemoryDC::SelectObject}{wxmemorydcselectobject}
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