A memory device context provides a means to draw graphics onto a bitmap. When drawing in to a mono-bitmap, using wxWHITE, wxWHITE_PEN and wxWHITE_BRUSH will draw the background colour (i.e. 0) whereas all other colours will draw the foreground colour (i.e. 1).

Derived from


Include files



A bitmap must be selected into the new memory DC before it may be used for anything. Typical usage is as follows:

  // Create a memory DC
  wxMemoryDC temp_dc;

  // 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);

Note that the memory DC must be deleted (or the bitmap selected out of it) before a bitmap can be reselected into another memory DC.

See also

wxBitmap, wxDC



Constructs a new memory device context.

Use the Ok 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.


void SelectObject(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 Blit to copy the bitmap to a window. For this purpose, you may find wxDC::DrawIcon 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.

ymasuda 平成17年11月19日