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 licence
   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     /**
  60         Constructs a new memory device context having the same characteristics
  61         as the given existing device context.
  62
  63         This constructor creates a memory device context @e compatible with @a
  64         dc in wxMSW, the argument is ignored in the other ports. If @a dc is
  65         @NULL, a device context compatible with the screen is created, just as
  66         with the default constructor.
  67      */
  68     wxMemoryDC(wxDC *dc);
  69
  70     /**
  71         Constructs a new memory device context and calls SelectObject() with
  72         the given bitmap.
  73
  74         Use the wxDC::IsOk() member to test whether the constructor was
  75         successful in creating a usable device context.
  76     */
  77     wxMemoryDC(wxBitmap& bitmap);
  78
  79     /**
  80         Works exactly like SelectObjectAsSource() but this is the function you
  81         should use when you select a bitmap because you want to modify it, e.g.
  82         drawing on this DC.
  83
  84         Using SelectObjectAsSource() when modifying the bitmap may incur some
  85         problems related to wxBitmap being a reference counted object (see
  86         @ref overview_refcount).
  87
  88         Before using the updated bitmap data, make sure to select it out of
  89         context first either by selecting ::wxNullBitmap into the device
  90         context or destroying the device context entirely.
  91
  92         If the bitmap is already selected in this device context, nothing is
  93         done. If it is selected in another context, the function asserts and
  94         drawing on the bitmap won't work correctly.
  95
  96         @see wxDC::DrawBitmap()
  97     */
  98     void SelectObject(wxBitmap& bitmap);
  99
 100     /**
 101         Selects the given bitmap into the device context, to use as the memory
 102         bitmap. Selecting the bitmap into a memory DC allows you to draw into
 103         the DC (and therefore the bitmap) and also to use wxDC::Blit() to copy
 104         the bitmap to a window. For this purpose, you may find wxDC::DrawIcon()
 105         easier to use instead.
 106
 107         If the argument is ::wxNullBitmap (or some other uninitialised wxBitmap)
 108         the current bitmap is selected out of the device context, and the
 109         original bitmap restored, allowing the current bitmap to be destroyed
 110         safely.
 111     */
 112     void SelectObjectAsSource(const wxBitmap& bitmap);
 113 };
 114