interface/wx/dcmemory.h

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        dcmemory.h
   3 // Purpose:     interface of wxMemoryDC
   4 // Author:      wxWidgets team
   5 // Licence:     wxWindows licence
   6 /////////////////////////////////////////////////////////////////////////////
   7
   8 /**
   9     @class wxMemoryDC
  10
  11     A memory device context provides a means to draw graphics onto a bitmap.
  12     When drawing in to a mono-bitmap, using @c wxWHITE, @c wxWHITE_PEN and
  13     @c wxWHITE_BRUSH will draw the background colour (i.e. 0) whereas all other
  14     colours will draw the foreground colour (i.e. 1).
  15
  16     A bitmap must be selected into the new memory DC before it may be used for
  17     anything. Typical usage is as follows:
  18
  19     @code
  20     // Create a memory DC
  21     wxMemoryDC temp_dc;
  22     temp_dc.SelectObject(test_bitmap);
  23
  24     // We can now draw into the memory DC...
  25     // Copy from this DC to another DC.
  26     old_dc.Blit(250, 50, BITMAP_WIDTH, BITMAP_HEIGHT, temp_dc, 0, 0);
  27     @endcode
  28
  29     Note that the memory DC must be deleted (or the bitmap selected out of it)
  30     before a bitmap can be reselected into another memory DC.
  31
  32     And, before performing any other operations on the bitmap data, the bitmap
  33     must be selected out of the memory DC:
  34
  35     @code
  36     temp_dc.SelectObject(wxNullBitmap);
  37     @endcode
  38
  39     This happens automatically when wxMemoryDC object goes out of scope.
  40
  41     @library{wxcore}
  42     @category{dc}
  43
  44     @see wxBitmap, wxDC
  45 */
  46 class wxMemoryDC : public wxDC
  47 {
  48 public:
  49     /**
  50         Constructs a new memory device context.
  51
  52         Use the wxDC::IsOk() member to test whether the constructor was
  53         successful in creating a usable device context. Don't forget to select
  54         a bitmap into the DC before drawing on it.
  55     */
  56     wxMemoryDC();
  57
  58     /**
  59         Constructs a new memory device context having the same characteristics
  60         as the given existing device context.
  61
  62         This constructor creates a memory device context @e compatible with @a
  63         dc in wxMSW, the argument is ignored in the other ports. If @a dc is
  64         @NULL, a device context compatible with the screen is created, just as
  65         with the default constructor.
  66      */
  67     wxMemoryDC(wxDC *dc);
  68
  69     /**
  70         Constructs a new memory device context and calls SelectObject() with
  71         the given bitmap.
  72
  73         Use the wxDC::IsOk() member to test whether the constructor was
  74         successful in creating a usable device context.
  75     */
  76     wxMemoryDC(wxBitmap& bitmap);
  77
  78     /**
  79         Works exactly like SelectObjectAsSource() but this is the function you
  80         should use when you select a bitmap because you want to modify it, e.g.
  81         drawing on this DC.
  82
  83         Using SelectObjectAsSource() when modifying the bitmap may incur some
  84         problems related to wxBitmap being a reference counted object (see
  85         @ref overview_refcount).
  86
  87         Before using the updated bitmap data, make sure to select it out of
  88         context first either by selecting ::wxNullBitmap into the device
  89         context or destroying the device context entirely.
  90
  91         If the bitmap is already selected in this device context, nothing is
  92         done. If it is selected in another context, the function asserts and
  93         drawing on the bitmap won't work correctly.
  94
  95         @see wxDC::DrawBitmap()
  96     */
  97     void SelectObject(wxBitmap& bitmap);
  98
  99     /**
 100         Selects the given bitmap into the device context, to use as the memory
 101         bitmap. Selecting the bitmap into a memory DC allows you to draw into
 102         the DC (and therefore the bitmap) and also to use wxDC::Blit() to copy
 103         the bitmap to a window. For this purpose, you may find wxDC::DrawIcon()
 104         easier to use instead.
 105
 106         If the argument is ::wxNullBitmap (or some other uninitialised wxBitmap)
 107         the current bitmap is selected out of the device context, and the
 108         original bitmap restored, allowing the current bitmap to be destroyed
 109         safely.
 110     */
 111     void SelectObjectAsSource(const wxBitmap& bitmap);
 112 };
 113