wxWidgets/interface/wx/dcmemory.h

/////////////////////////////////////////////////////////////////////////////
// Name:        dcmemory.h
// Purpose:     interface of wxMemoryDC
// Author:      wxWidgets team
// Licence:     wxWindows licence
/////////////////////////////////////////////////////////////////////////////

/**
    @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 incur some
        problems related to wxBitmap being a reference counted object (see
        @ref overview_refcount).

        Before using the updated bitmap data, make sure to select it out of
        context first either by selecting ::wxNullBitmap into the device
        context or destroying the device context entirely.

        If the bitmap is already selected in this device context, nothing is
        done. If it is selected in another context, the function asserts and
        drawing on the bitmap won't work correctly.

        @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);
};