wxBufferedDC

This class provides a simple way to avoid flicker: when drawing on it, everything is in fact first drawn on an in-memory buffer (a wxBitmap) and then copied to the screen, using the associated wxDC, only once, when this object is destroyed. wxBufferedDC itself is typically associated with wxClientDC, if you want to use it in your EVT_PAINT handler, you should look at wxBufferedPaintDC instead.

When used like this, a valid dc must be specified in the constructor while the buffer bitmap doesn't have to be explicitly provided, by default this class will allocate the bitmap of required size itself. However using a dedicated bitmap can speed up the redrawing process by eliminating the repeated creation and destruction of a possibly big bitmap. Otherwise, wxBufferedDC can be used in the same way as any other device context.

There is another possible use for wxBufferedDC is to use it to maintain a backing store for the window contents. In this case, the associated dc may be NULL but a valid backing store bitmap should be specified.

Finally, please note that GTK+ 2.0 as well as OS X provide double buffering themselves natively. You can either use wxWindow::IsDoubleBuffered to determine whether you need to use buffering or not, or use wxAutoBufferedPaintDC to avoid needless double buffering on the systems which already do it automatically.

Derived from

wxMemoryDC
wxDC
wxObject

Include files

<wx/dcbuffer.h>

See also

wxDC, wxMemoryDC, wxBufferedPaintDC, wxAutoBufferedPaintDC

Members

wxBufferedDC::wxBufferedDC
wxBufferedDC::Init
wxBufferedDC::~wxBufferedDC

wxBufferedDC::wxBufferedDC

wxBufferedDC()

wxBufferedDC(wxDC *dc, const wxSize& area, int style = wxBUFFER_CLIENT_AREA)

wxBufferedDC(wxDC *dc, wxBitmap& buffer, int style = wxBUFFER_CLIENT_AREA)

If you use the first, default, constructor, you must call one of the Init methods later in order to use the object.

The other constructors initialize the object immediately and Init() must not be called after using them.

Parameters

dc

The underlying DC: everything drawn to this object will be flushed to this DC when this object is destroyed. You may pass NULL in order to just initialize the buffer, and not flush it.

area

The size of the bitmap to be used for buffering (this bitmap is created internally when it is not given explicitly).

buffer

Explicitly provided bitmap to be used for buffering: this is the most efficient solution as the bitmap doesn't have to be recreated each time but it also requires more memory as the bitmap is never freed. The bitmap should have appropriate size, anything drawn outside of its bounds is clipped.

style

wxBUFFER_CLIENT_AREA to indicate that just the client area of the window is buffered, or wxBUFFER_VIRTUAL_AREA to indicate that the buffer bitmap covers the virtual area (in which case PrepareDC is automatically called for the actual window device context).

wxBufferedDC::Init

void Init(wxDC *dc, const wxSize& area, int style = wxBUFFER_CLIENT_AREA)

void Init(wxDC *dc, wxBitmap& buffer, int style = wxBUFFER_CLIENT_AREA)

These functions initialize the object created using the default constructor. Please see constructors documentation for details.

wxBufferedDC::~wxBufferedDC

Copies everything drawn on the DC so far to the underlying DC associated with this object, if any.