interface/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     @wxheader{dcmemory.h}
  12
  13     A memory device context provides a means to draw graphics onto a bitmap.
  14     When drawing in to a mono-bitmap, using @c wxWHITE, @c wxWHITE_PEN and
  15     @c wxWHITE_BRUSH will draw the background colour (i.e. 0) whereas all other
  16     colours will draw the foreground colour (i.e. 1).
  17
  18     A bitmap must be selected into the new memory DC before it may be used for
  19     anything. Typical usage is as follows:
  20
  21     @code
  22     // Create a memory DC
  23     wxMemoryDC temp_dc;
  24     temp_dc.SelectObject(test_bitmap);
  25
  26     // We can now draw into the memory DC...
  27     // Copy from this DC to another DC.
  28     old_dc.Blit(250, 50, BITMAP_WIDTH, BITMAP_HEIGHT, temp_dc, 0, 0);
  29     @endcode
  30
  31     Note that the memory DC must be deleted (or the bitmap selected out of it)
  32     before a bitmap can be reselected into another memory DC.
  33
  34     And, before performing any other operations on the bitmap data, the bitmap
  35     must be selected out of the memory DC:
  36
  37     @code
  38     temp_dc.SelectObject(wxNullBitmap);
  39     @endcode
  40
  41     This happens automatically when wxMemoryDC object goes out of scope.
  42
  43     @library{wxcore}
  44     @category{dc}
  45
  46     @see wxBitmap, wxDC
  47 */
  48 class wxMemoryDC : public wxDC
  49 {
  50 public:
  51     /**
  52         Constructs a new memory device context.
  53
  54         Use the wxDC::Ok() member to test whether the constructor was
  55         successful in creating a usable device context. Don't forget to select
  56         a bitmap into the DC before drawing on it.
  57     */
  58     wxMemoryDC();
  59     /**
  60         Constructs a new memory device context and calls SelectObject() with
  61         the given bitmap.
  62
  63         Use the wxDC::Ok() member to test whether the constructor was
  64         successful in creating a usable device context.
  65     */
  66     wxMemoryDC(wxBitmap& bitmap);
  67
  68     /**
  69         Works exactly like SelectObjectAsSource() but this is the function you
  70         should use when you select a bitmap because you want to modify it, e.g.
  71         drawing on this DC.
  72
  73         Using SelectObjectAsSource() when modifying the bitmap may incurr some
  74         problems related to wxBitmap being a reference counted object (see
  75         @ref overview_refcount).
  76
  77         Also, before using the updated bitmap data, make sure to select it out
  78         of context first (for example by selecting wxNullBitmap into the device
  79         context).
  80
  81         @see wxDC::DrawBitmap()
  82     */
  83     void SelectObject(wxBitmap& bitmap);
  84
  85     /**
  86         Selects the given bitmap into the device context, to use as the memory
  87         bitmap. Selecting the bitmap into a memory DC allows you to draw into
  88         the DC (and therefore the bitmap) and also to use wxDC::Blit() to copy
  89         the bitmap to a window. For this purpose, you may find wxDC::DrawIcon()
  90         easier to use instead.
  91
  92         If the argument is wxNullBitmap (or some other uninitialised wxBitmap)
  93         the current bitmap is selected out of the device context, and the
  94         original bitmap restored, allowing the current bitmap to be destroyed
  95         safely.
  96     */
  97     void SelectObjectAsSource(const wxBitmap& bitmap);
  98 };
  99