wxWidgets/interface/wx/dcmemory.h

/////////////////////////////////////////////////////////////////////////////
// Name:        dcmemory.h
// Purpose:     interface of wxMemoryDC
// Author:      wxWidgets team
// RCS-ID:      $Id$
// Licence:     wxWindows license
/////////////////////////////////////////////////////////////////////////////

/**
    @class wxMemoryDC

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

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

    @code
    // Create a memory DC
    wxMemoryDC temp_dc;
    temp_dc.SelectObject(test_bitmap);

    // 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);
    @endcode

    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.

    And, before performing any other operations on the bitmap data, the bitmap
    must be selected out of the memory DC:

    @code
    temp_dc.SelectObject(wxNullBitmap);
    @endcode

    This happens automatically when wxMemoryDC object goes out of scope.

    @library{wxcore}
    @category{dc}

    @see wxBitmap, wxDC
*/
class wxMemoryDC : public wxDC
{
public:
    /**
        Constructs a new memory device context.

        Use the wxDC::IsOk() 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.
    */
    wxMemoryDC();

    /**
        Constructs a new memory device context having the same characteristics
        as the given existing device context.

        This constructor creates a memory device context @e compatible with @a
        dc in wxMSW, the argument is ignored in the other ports. If @a dc is
        @NULL, a device context compatible with the screen is created, just as
        with the default constructor.
     */
    wxMemoryDC(wxDC *dc);

    /**
        Constructs a new memory device context and calls SelectObject() with
        the given bitmap.

        Use the wxDC::IsOk() member to test whether the constructor was
        successful in creating a usable device context.
    */
    wxMemoryDC(wxBitmap& bitmap);

    /**
        Works exactly like SelectObjectAsSource() but this is the function you
        should use when you select a bitmap because you want to modify it, e.g.
        drawing on this DC.

        Using SelectObjectAsSource() when modifying the bitmap may incurr some
        problems related to wxBitmap being a reference counted object (see
        @ref overview_refcount).

        Also, before using the updated bitmap data, make sure to select it out
        of context first (for example by selecting ::wxNullBitmap into the device
        context).

        @see wxDC::DrawBitmap()
    */
    void SelectObject(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 wxDC::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.
    */
    void SelectObjectAsSource(const wxBitmap& bitmap);
};