interface/wx/dcmemory.h

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        dcmemory.h
   3 // Purpose:     interface of wxMemoryDC
   4 // Author:      wxWidgets team
   5 // RCS-ID:      $Id$
   6 // Licence:     wxWindows license
   7 /////////////////////////////////////////////////////////////////////////////
   8
   9 /**
  10     @class wxMemoryDC
  11
  12     A memory device context provides a means to draw graphics onto a bitmap.
  13     When drawing in to a mono-bitmap, using @c wxWHITE, @c wxWHITE_PEN and
  14     @c wxWHITE_BRUSH will draw the background colour (i.e. 0) whereas all other
  15     colours will draw the foreground colour (i.e. 1).
  16
  17     A bitmap must be selected into the new memory DC before it may be used for
  18     anything. Typical usage is as follows:
  19
  20     @code
  21     // Create a memory DC
  22     wxMemoryDC temp_dc;
  23     temp_dc.SelectObject(test_bitmap);
  24
  25     // We can now draw into the memory DC...
  26     // Copy from this DC to another DC.
  27     old_dc.Blit(250, 50, BITMAP_WIDTH, BITMAP_HEIGHT, temp_dc, 0, 0);
  28     @endcode
  29
  30     Note that the memory DC must be deleted (or the bitmap selected out of it)
  31     before a bitmap can be reselected into another memory DC.
  32
  33     And, before performing any other operations on the bitmap data, the bitmap
  34     must be selected out of the memory DC:
  35
  36     @code
  37     temp_dc.SelectObject(wxNullBitmap);
  38     @endcode
  39
  40     This happens automatically when wxMemoryDC object goes out of scope.
  41
  42     @library{wxcore}
  43     @category{dc}
  44
  45     @see wxBitmap, wxDC
  46 */
  47 class wxMemoryDC : public wxDC
  48 {
  49 public:
  50     /**
  51         Constructs a new memory device context.
  52
  53         Use the wxDC::IsOk() member to test whether the constructor was
  54         successful in creating a usable device context. Don't forget to select
  55         a bitmap into the DC before drawing on it.
  56     */
  57     wxMemoryDC();
  58     /**
  59         Constructs a new memory device context and calls SelectObject() with
  60         the given bitmap.
  61
  62         Use the wxDC::IsOk() member to test whether the constructor was
  63         successful in creating a usable device context.
  64     */
  65     wxMemoryDC(wxBitmap& bitmap);
  66
  67     /**
  68         Works exactly like SelectObjectAsSource() but this is the function you
  69         should use when you select a bitmap because you want to modify it, e.g.
  70         drawing on this DC.
  71
  72         Using SelectObjectAsSource() when modifying the bitmap may incurr some
  73         problems related to wxBitmap being a reference counted object (see
  74         @ref overview_refcount).
  75
  76         Also, before using the updated bitmap data, make sure to select it out
  77         of context first (for example by selecting ::wxNullBitmap into the device
  78         context).
  79
  80         @see wxDC::DrawBitmap()
  81     */
  82     void SelectObject(wxBitmap& bitmap);
  83
  84     /**
  85         Selects the given bitmap into the device context, to use as the memory
  86         bitmap. Selecting the bitmap into a memory DC allows you to draw into
  87         the DC (and therefore the bitmap) and also to use wxDC::Blit() to copy
  88         the bitmap to a window. For this purpose, you may find wxDC::DrawIcon()
  89         easier to use instead.
  90
  91         If the argument is ::wxNullBitmap (or some other uninitialised wxBitmap)
  92         the current bitmap is selected out of the device context, and the
  93         original bitmap restored, allowing the current bitmap to be destroyed
  94         safely.
  95     */
  96     void SelectObjectAsSource(const wxBitmap& bitmap);
  97 };
  98