f20f1e944c
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@49561 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
113 lines
3.6 KiB
TeX
113 lines
3.6 KiB
TeX
\section{\class{wxMemoryDC}}\label{wxmemorydc}
|
|
|
|
A memory device context provides a means to draw graphics onto a bitmap. When
|
|
drawing in to a mono-bitmap, using {\tt wxWHITE}, {\tt wxWHITE\_PEN} and
|
|
{\tt wxWHITE\_BRUSH}
|
|
will draw the background colour (i.e. 0) whereas all other colours will draw the
|
|
foreground colour (i.e. 1).
|
|
|
|
\wxheading{Derived from}
|
|
|
|
\helpref{wxDC}{wxdc}\\
|
|
\helpref{wxObject}{wxobject}
|
|
|
|
\wxheading{Include files}
|
|
|
|
<wx/dcmemory.h>
|
|
|
|
\wxheading{Library}
|
|
|
|
\helpref{wxCore}{librarieslist}
|
|
|
|
\wxheading{Remarks}
|
|
|
|
A bitmap must be selected into the new memory DC before it may be used
|
|
for anything. Typical usage is as follows:
|
|
|
|
\begin{verbatim}
|
|
// Create a memory DC
|
|
wxMemoryDC temp_dc;
|
|
temp_dc.SelectObject(test_bitmap);
|
|
|
|
// We can now draw into the memory DC...
|
|
// Copy from this DC to another DC.
|
|
old_dc.Blit(250, 50, BITMAP_WIDTH, BITMAP_HEIGHT, temp_dc, 0, 0);
|
|
\end{verbatim}
|
|
|
|
Note that the memory DC {\it must} be deleted (or the bitmap selected out of it) before a bitmap
|
|
can be reselected into another memory DC.
|
|
|
|
And, before performing any other operations on the bitmap data, the bitmap must
|
|
be selected out of the memory DC:
|
|
|
|
\begin{verbatim}
|
|
temp_dc.SelectObject(wxNullBitmap)
|
|
\end{verbatim}
|
|
|
|
(this happens automatically when wxMemoryDC object goes out of scope).
|
|
|
|
|
|
\wxheading{See also}
|
|
|
|
\helpref{wxBitmap}{wxbitmap}, \helpref{wxDC}{wxdc}
|
|
|
|
\latexignore{\rtfignore{\wxheading{Members}}}
|
|
|
|
\membersection{wxMemoryDC::wxMemoryDC}\label{wxmemorydcctor}
|
|
|
|
\func{}{wxMemoryDC}{\void}
|
|
|
|
Constructs a new memory device context.
|
|
|
|
Use the \helpref{IsOk}{wxdcisok} member to test whether the constructor was successful
|
|
in creating a usable device context.
|
|
Don't forget to select a bitmap into the DC before drawing on it.
|
|
|
|
\func{}{wxMemoryDC}{\param{wxBitmap\& }{bitmap}}
|
|
|
|
Constructs a new memory device context and calls \helpref{SelectObject}{wxmemorydcselectobject}
|
|
with the given bitmap.
|
|
Use the \helpref{IsOk}{wxdcisok} member to test whether the constructor was successful
|
|
in creating a usable device context.
|
|
|
|
|
|
\membersection{wxMemoryDC::SelectObject}\label{wxmemorydcselectobject}
|
|
|
|
\func{void}{SelectObject}{\param{wxBitmap\& }{bitmap}}
|
|
|
|
Works exactly like \helpref{SelectObjectAsSource}{wxmemorydcselectobjectassource} but
|
|
this is the function you should use when you select a bitmap because you want to modify
|
|
it, e.g. drawing on this DC.
|
|
|
|
Using \helpref{SelectObjectAsSource}{wxmemorydcselectobjectassource} when modifying
|
|
the bitmap may incurr some problems related to wxBitmap being a reference counted object
|
|
(see \helpref{reference counting overview}{trefcount}).
|
|
|
|
Also, before using the updated bitmap data, make sure to select it out of context first
|
|
(for example by selecting wxNullBitmap into the device context).
|
|
|
|
\wxheading{See also}
|
|
|
|
\helpref{wxDC::DrawBitmap}{wxdcdrawbitmap}
|
|
|
|
|
|
|
|
\membersection{wxMemoryDC::SelectObjectAsSource}\label{wxmemorydcselectobjectassource}
|
|
|
|
\func{void}{SelectObjectAsSource}{\param{const wxBitmap\& }{bitmap}}
|
|
|
|
Selects the given bitmap into the device context, to use as the memory
|
|
bitmap. Selecting the bitmap into a memory DC allows you to draw into
|
|
the DC (and therefore the bitmap) and also to use \helpref{wxDC::Blit}{wxdcblit} to copy
|
|
the bitmap to a window. For this purpose, you may find \helpref{wxDC::DrawIcon}{wxdcdrawicon}\rtfsp
|
|
easier to use instead.
|
|
|
|
If the argument is wxNullBitmap (or some other uninitialised wxBitmap) the current bitmap is
|
|
selected out of the device context, and the original bitmap restored, allowing the current bitmap to
|
|
be destroyed safely.
|
|
|
|
\wxheading{See also}
|
|
|
|
\helpref{wxMemoryDC::SelectObject}{wxmemorydcselectobject}
|
|
|