fixed memory allocation code of wxStreamBuffer to not realloc() new[]ed memory any...

[wxWidgets.git] / src / msw / bitmap.cpp

/////////////////////////////////////////////////////////////////////////////
// Name:        bitmap.cpp
// Purpose:     wxBitmap
// Author:      Julian Smart
// Modified by:
// Created:     04/01/98
// RCS-ID:      $Id$
// Copyright:   (c) Julian Smart and Markus Holzem
// Licence:     wxWindows license
/////////////////////////////////////////////////////////////////////////////

// ============================================================================
// declarations
// ============================================================================

// ----------------------------------------------------------------------------
// headers
// ----------------------------------------------------------------------------

#ifdef __GNUG__
    #pragma implementation "bitmap.h"
#endif

// For compilers that support precompilation, includes "wx.h".
#include "wx/wxprec.h"

#ifdef __BORLANDC__
    #pragma hdrstop
#endif

#ifndef WX_PRECOMP
    #include <stdio.h>

    #include "wx/list.h"
    #include "wx/utils.h"
    #include "wx/app.h"
    #include "wx/palette.h"
    #include "wx/dcmemory.h"
    #include "wx/bitmap.h"
    #include "wx/icon.h"
#endif

#include "wx/msw/private.h"
#include "wx/log.h"

#include "wx/msw/dib.h"
#include "wx/image.h"

// missing from mingw32 header
#ifndef CLR_INVALID
    #define CLR_INVALID ((COLORREF)-1)
#endif // no CLR_INVALID

// ----------------------------------------------------------------------------
// macros
// ----------------------------------------------------------------------------

IMPLEMENT_DYNAMIC_CLASS(wxBitmap, wxGDIObject)
IMPLEMENT_DYNAMIC_CLASS(wxMask, wxObject)

IMPLEMENT_DYNAMIC_CLASS(wxBitmapHandler, wxObject)

// ============================================================================
// implementation
// ============================================================================

// ----------------------------------------------------------------------------
// wxBitmapRefData
// ----------------------------------------------------------------------------

wxBitmapRefData::wxBitmapRefData()
{
    m_quality = 0;
    m_selectedInto = NULL;
    m_numColors = 0;
    m_bitmapMask = NULL;
    m_hBitmap = (WXHBITMAP) NULL;
}

void wxBitmapRefData::Free()
{
    wxASSERT_MSG( !m_selectedInto,
                  wxT("deleting bitmap still selected into wxMemoryDC") );

    if ( m_hBitmap)
    {
        if ( !::DeleteObject((HBITMAP)m_hBitmap) )
        {
            wxLogLastError(wxT("DeleteObject(hbitmap)"));
        }
    }

    delete m_bitmapMask;
    m_bitmapMask = NULL;
}

// ----------------------------------------------------------------------------
// wxBitmap creation
// ----------------------------------------------------------------------------

// this function should be called from all wxBitmap ctors
void wxBitmap::Init()
{
    // m_refData = NULL; done in the base class ctor

    if ( wxTheBitmapList )
        wxTheBitmapList->AddBitmap(this);
}

#ifdef __WIN32__

bool wxBitmap::CopyFromIconOrCursor(const wxGDIImage& icon)
{
    // it may be either HICON or HCURSOR
    HICON hicon = (HICON)icon.GetHandle();

    ICONINFO iconInfo;
    if ( !::GetIconInfo(hicon, &iconInfo) )
    {
        wxLogLastError(wxT("GetIconInfo"));

        return FALSE;
    }

    wxBitmapRefData *refData = new wxBitmapRefData;
    m_refData = refData;

    int w = icon.GetWidth(),
        h = icon.GetHeight();

    refData->m_width = w;
    refData->m_height = h;
    refData->m_depth = wxDisplayDepth();

    refData->m_hBitmap = (WXHBITMAP)iconInfo.hbmColor;

    // the mask returned by GetIconInfo() is inversed compared to the usual
    // wxWin convention
    refData->m_bitmapMask = new wxMask((WXHBITMAP)
                                        wxInvertMask(iconInfo.hbmMask, w, h));

#if WXWIN_COMPATIBILITY_2
    refData->m_ok = TRUE;
#endif // WXWIN_COMPATIBILITY_2

    return TRUE;
}

#endif // Win32

bool wxBitmap::CopyFromCursor(const wxCursor& cursor)
{
    UnRef();

    if ( !cursor.Ok() )
        return FALSE;

#ifdef __WIN16__
    wxFAIL_MSG( _T("don't know how to convert cursor to bitmap") );

    return FALSE;
#else
    return CopyFromIconOrCursor(cursor);
#endif // Win16
}

bool wxBitmap::CopyFromIcon(const wxIcon& icon)
{
    UnRef();

    if ( !icon.Ok() )
        return FALSE;

    // GetIconInfo() doesn't exist under Win16 and I don't know any other way
    // to create a bitmap from icon there - but using this way we won't have
    // the mask (FIXME)
#ifdef __WIN16__
    int width = icon.GetWidth(),
        height = icon.GetHeight();

    // copy the icon to the bitmap
    ScreenHDC hdcScreen;
    HDC hdc = ::CreateCompatibleDC(hdcScreen);
    HBITMAP hbitmap = ::CreateCompatibleBitmap(hdcScreen, width, height);
    HBITMAP hbmpOld = (HBITMAP)::SelectObject(hdc, hbitmap);

    ::DrawIcon(hdc, 0, 0, GetHiconOf(icon));

    ::SelectObject(hdc, hbmpOld);
    ::DeleteDC(hdc);

    wxBitmapRefData *refData = new wxBitmapRefData;
    m_refData = refData;

    refData->m_width = width;
    refData->m_height = height;
    refData->m_depth = wxDisplayDepth();

    refData->m_hBitmap = (WXHBITMAP)hbitmap;

#if WXWIN_COMPATIBILITY_2
    refData->m_ok = TRUE;
#endif // WXWIN_COMPATIBILITY_2

    return TRUE;
#else // Win32
    return CopyFromIconOrCursor(icon);
#endif // Win16/Win32
}

wxBitmap::~wxBitmap()
{
    if (wxTheBitmapList)
        wxTheBitmapList->DeleteObject(this);
}

wxBitmap::wxBitmap(const char bits[], int width, int height, int depth)
{
    Init();

    wxBitmapRefData *refData = new wxBitmapRefData;
    m_refData = refData;

    refData->m_width = width;
    refData->m_height = height;
    refData->m_depth = depth;
    refData->m_numColors = 0;
    refData->m_selectedInto = NULL;

    char *data;
    if ( depth == 1 )
    {
        // we assume that it is in XBM format which is not quite the same as
        // the format CreateBitmap() wants because the order of bytes in the
        // line is inversed!
        static const size_t bytesPerLine = (width + 7) / 8;
        static const size_t padding = bytesPerLine % 2;
        static const size_t len = height * ( padding + bytesPerLine );
        data = (char *)malloc(len);
        const char *src = bits;
        char *dst = data;

        for ( int rows = 0; rows < height; rows++ )
        {
            for ( size_t cols = 0; cols < bytesPerLine; cols++ )
            {
                unsigned char val = *src++;
                unsigned char reversed = 0;

                for ( int bits = 0; bits < 8; bits++)
                {
                    reversed <<= 1;
                    reversed |= (val & 0x01);
                    val >>= 1;
                }
                *dst++ = reversed;
            }

            if ( padding )
                *dst++ = 0;
        }
    }
    else
    {
        // bits should already be in Windows standard format
        data = (char *)bits;    // const_cast is harmless
    }

    HBITMAP hbmp = ::CreateBitmap(width, height, 1, depth, data);
    if ( !hbmp )
    {
        wxLogLastError(wxT("CreateBitmap"));
    }

    if ( data != bits )
    {
        free(data);
    }

    SetHBITMAP((WXHBITMAP)hbmp);
}

// Create from XPM data
bool wxBitmap::CreateFromXpm(const char **data)
{
    Init();

    return Create((void *)data, wxBITMAP_TYPE_XPM_DATA, 0, 0, 0);
}

wxBitmap::wxBitmap(int w, int h, int d)
{
    Init();

    (void)Create(w, h, d);
}

wxBitmap::wxBitmap(void *data, long type, int width, int height, int depth)
{
    Init();

    (void)Create(data, type, width, height, depth);
}

wxBitmap::wxBitmap(const wxString& filename, long type)
{
    Init();

    LoadFile(filename, (int)type);
}

bool wxBitmap::Create(int w, int h, int d)
{
    UnRef();

    m_refData = new wxBitmapRefData;

    GetBitmapData()->m_width = w;
    GetBitmapData()->m_height = h;
    GetBitmapData()->m_depth = d;

    HBITMAP hbmp;

    if ( d > 0 )
    {
        hbmp = ::CreateBitmap(w, h, 1, d, NULL);
        if ( !hbmp )
        {
            wxLogLastError(wxT("CreateBitmap"));
        }
    }
    else
    {
        ScreenHDC dc;
        hbmp = ::CreateCompatibleBitmap(dc, w, h);
        if ( !hbmp )
        {
            wxLogLastError(wxT("CreateCompatibleBitmap"));
        }

        GetBitmapData()->m_depth = wxDisplayDepth();
    }

    SetHBITMAP((WXHBITMAP)hbmp);

#if WXWIN_COMPATIBILITY_2
    GetBitmapData()->m_ok = hbmp != 0;
#endif // WXWIN_COMPATIBILITY_2

    return Ok();
}

bool wxBitmap::LoadFile(const wxString& filename, long type)
{
    UnRef();

    wxBitmapHandler *handler = wxDynamicCast(FindHandler(type), wxBitmapHandler);

    if ( handler )
    {
        m_refData = new wxBitmapRefData;

        return handler->LoadFile(this, filename, type, -1, -1);
    }
    else
    {
        wxImage image;
        if ( !image.LoadFile( filename, type ) || !image.Ok() )
            return FALSE;

        *this = image.ConvertToBitmap();

        return TRUE;
    }
}

bool wxBitmap::Create(void *data, long type, int width, int height, int depth)
{
    UnRef();

    wxBitmapHandler *handler = wxDynamicCast(FindHandler(type), wxBitmapHandler);

    if ( !handler )
    {
        wxLogDebug(wxT("Failed to create bitmap: no bitmap handler for type %d defined."), type);

        return FALSE;
    }

    m_refData = new wxBitmapRefData;

    return handler->Create(this, data, type, width, height, depth);
}

bool wxBitmap::SaveFile(const wxString& filename, int type, const wxPalette *palette)
{
    wxBitmapHandler *handler = wxDynamicCast(FindHandler(type), wxBitmapHandler);

    if ( handler )
    {
        return handler->SaveFile(this, filename, type, palette);
    }
    else
    {
        // FIXME what about palette? shouldn't we use it?
        wxImage image( *this );
        if (!image.Ok())
            return FALSE;

        return image.SaveFile( filename, type );
    }
}

// ----------------------------------------------------------------------------
// sub bitmap extraction
// ----------------------------------------------------------------------------

wxBitmap wxBitmap::GetSubBitmap( const wxRect& rect) const
{
    wxCHECK_MSG( Ok() &&
                 (rect.x >= 0) && (rect.y >= 0) &&
                 (rect.x+rect.width <= GetWidth()) &&
                 (rect.y+rect.height <= GetHeight()),
                 wxNullBitmap, wxT("Invalid bitmap or bitmap region") );

    wxBitmap ret( rect.width, rect.height, GetDepth() );
    wxASSERT_MSG( ret.Ok(), wxT("GetSubBitmap error") );

    // copy bitmap data
    HDC dcSrc = ::CreateCompatibleDC(NULL);
    HDC dcDst = ::CreateCompatibleDC(NULL);
    SelectObject(dcSrc, (HBITMAP) GetHBITMAP());
    SelectObject(dcDst, (HBITMAP) ret.GetHBITMAP());
    BitBlt(dcDst, 0, 0, rect.width, rect.height, dcSrc, rect.x, rect.y, SRCCOPY);

    // copy mask if there is one
    if (GetMask())
    {
        HBITMAP hbmpMask = ::CreateBitmap(rect.width, rect.height, 1, 1, 0);

        SelectObject(dcSrc, (HBITMAP) GetMask()->GetMaskBitmap());
        SelectObject(dcDst, (HBITMAP) hbmpMask);
        BitBlt(dcDst, 0, 0, rect.width, rect.height, dcSrc, rect.x, rect.y, SRCCOPY);

        wxMask *mask = new wxMask((WXHBITMAP) hbmpMask);
        ret.SetMask(mask);
    }

    SelectObject(dcDst, NULL);
    SelectObject(dcSrc, NULL);
    DeleteDC(dcDst);
    DeleteDC(dcSrc);

    return ret;
}

// ----------------------------------------------------------------------------
// wxBitmap accessors
// ----------------------------------------------------------------------------

void wxBitmap::SetQuality(int q)
{
    EnsureHasData();

    GetBitmapData()->m_quality = q;
}

#if WXWIN_COMPATIBILITY_2
void wxBitmap::SetOk(bool isOk)
{
    EnsureHasData();

    GetBitmapData()->m_ok = isOk;
}
#endif // WXWIN_COMPATIBILITY_2

void wxBitmap::SetPalette(const wxPalette& palette)
{
    EnsureHasData();

    GetBitmapData()->m_bitmapPalette = palette;
}

void wxBitmap::SetMask(wxMask *mask)
{
    EnsureHasData();

    GetBitmapData()->m_bitmapMask = mask;
}

// Creates a bitmap that matches the device context, from
// an arbitray bitmap. At present, the original bitmap must have an
// associated palette. TODO: use a default palette if no palette exists.
// Contributed by Frederic Villeneuve <frederic.villeneuve@natinst.com>
wxBitmap wxBitmap::GetBitmapForDC(wxDC& dc) const
{
    wxMemoryDC      memDC;
    wxBitmap        tmpBitmap(GetWidth(), GetHeight(), dc.GetDepth());
    HPALETTE        hPal = (HPALETTE) NULL;
    LPBITMAPINFO    lpDib;
    void            *lpBits = (void*) NULL;

    if( GetPalette() && GetPalette()->Ok() )
    {
        tmpBitmap.SetPalette(*GetPalette());
        memDC.SelectObject(tmpBitmap);
        memDC.SetPalette(*GetPalette());
        hPal = (HPALETTE)GetPalette()->GetHPALETTE();
    }
    else
    {
        hPal = (HPALETTE) ::GetStockObject(DEFAULT_PALETTE);
        wxPalette palette;
        palette.SetHPALETTE( (WXHPALETTE)hPal );
        tmpBitmap.SetPalette( palette );
        memDC.SelectObject(tmpBitmap);
        memDC.SetPalette( palette );
    }

    // set the height negative because in a DIB the order of the lines is
    // reversed
    if ( !wxCreateDIB(GetWidth(), -GetHeight(), GetDepth(), hPal, &lpDib) )
    {
        return wxNullBitmap;
    }

    lpBits = malloc(lpDib->bmiHeader.biSizeImage);

    ::GetBitmapBits(GetHbitmap(), lpDib->bmiHeader.biSizeImage, lpBits);

    ::SetDIBitsToDevice(GetHdcOf(memDC), 0, 0,
                        GetWidth(), GetHeight(),
                        0, 0, 0, GetHeight(),
                        lpBits, lpDib, DIB_RGB_COLORS);

    free(lpBits);

    wxFreeDIB(lpDib);

    return tmpBitmap;
}

// ----------------------------------------------------------------------------
// wxMask
// ----------------------------------------------------------------------------

wxMask::wxMask()
{
    m_maskBitmap = 0;
}

// Construct a mask from a bitmap and a colour indicating
// the transparent area
wxMask::wxMask(const wxBitmap& bitmap, const wxColour& colour)
{
    m_maskBitmap = 0;
    Create(bitmap, colour);
}

// Construct a mask from a bitmap and a palette index indicating
// the transparent area
wxMask::wxMask(const wxBitmap& bitmap, int paletteIndex)
{
    m_maskBitmap = 0;
    Create(bitmap, paletteIndex);
}

// Construct a mask from a mono bitmap (copies the bitmap).
wxMask::wxMask(const wxBitmap& bitmap)
{
    m_maskBitmap = 0;
    Create(bitmap);
}

wxMask::~wxMask()
{
    if ( m_maskBitmap )
        ::DeleteObject((HBITMAP) m_maskBitmap);
}

// Create a mask from a mono bitmap (copies the bitmap).
bool wxMask::Create(const wxBitmap& bitmap)
{
    wxCHECK_MSG( bitmap.Ok() && bitmap.GetDepth() == 1, FALSE,
                 _T("can't create mask from invalid or not monochrome bitmap") );

    if ( m_maskBitmap )
    {
        ::DeleteObject((HBITMAP) m_maskBitmap);
        m_maskBitmap = 0;
    }

    m_maskBitmap = (WXHBITMAP) CreateBitmap(
                                            bitmap.GetWidth(),
                                            bitmap.GetHeight(),
                                            1, 1, 0
                                           );
    HDC srcDC = CreateCompatibleDC(0);
    SelectObject(srcDC, (HBITMAP) bitmap.GetHBITMAP());
    HDC destDC = CreateCompatibleDC(0);
    SelectObject(destDC, (HBITMAP) m_maskBitmap);
    BitBlt(destDC, 0, 0, bitmap.GetWidth(), bitmap.GetHeight(), srcDC, 0, 0, SRCCOPY);
    SelectObject(srcDC, 0);
    DeleteDC(srcDC);
    SelectObject(destDC, 0);
    DeleteDC(destDC);
    return TRUE;
}

// Create a mask from a bitmap and a palette index indicating
// the transparent area
bool wxMask::Create(const wxBitmap& bitmap, int paletteIndex)
{
    if ( m_maskBitmap )
    {
        ::DeleteObject((HBITMAP) m_maskBitmap);
        m_maskBitmap = 0;
    }
    if (bitmap.Ok() && bitmap.GetPalette()->Ok())
    {
        unsigned char red, green, blue;
        if (bitmap.GetPalette()->GetRGB(paletteIndex, &red, &green, &blue))
        {
            wxColour transparentColour(red, green, blue);
            return Create(bitmap, transparentColour);
        }
    }
    return FALSE;
}

// Create a mask from a bitmap and a colour indicating
// the transparent area
bool wxMask::Create(const wxBitmap& bitmap, const wxColour& colour)
{
    wxCHECK_MSG( bitmap.Ok(), FALSE, _T("invalid bitmap in wxMask::Create") );

    if ( m_maskBitmap )
    {
        ::DeleteObject((HBITMAP) m_maskBitmap);
        m_maskBitmap = 0;
    }

    int width = bitmap.GetWidth(),
        height = bitmap.GetHeight();

    // scan the bitmap for the transparent colour and set the corresponding
    // pixels in the mask to BLACK and the rest to WHITE
    COLORREF maskColour = wxColourToRGB(colour);
    m_maskBitmap = (WXHBITMAP)::CreateBitmap(width, height, 1, 1, 0);

    HDC srcDC = ::CreateCompatibleDC(NULL);
    HDC destDC = ::CreateCompatibleDC(NULL);
    if ( !srcDC || !destDC )
    {
        wxLogLastError(wxT("CreateCompatibleDC"));
    }

    bool ok = TRUE;

    HGDIOBJ hbmpSrcOld = ::SelectObject(srcDC, GetHbitmapOf(bitmap));
    if ( !hbmpSrcOld )
    {
        wxLogLastError(wxT("SelectObject"));

        ok = FALSE;
    }

    HGDIOBJ hbmpDstOld = ::SelectObject(destDC, (HBITMAP)m_maskBitmap);
    if ( !hbmpDstOld )
    {
        wxLogLastError(wxT("SelectObject"));

        ok = FALSE;
    }

    // this is not very efficient, but I can't think of a better way of doing
    // it
    for ( int w = 0; ok && (w < width); w++ )
    {
        for ( int h = 0; ok && (h < height); h++ )
        {
            COLORREF col = GetPixel(srcDC, w, h);
            if ( col == CLR_INVALID )
            {
                wxLogLastError(wxT("GetPixel"));

                // doesn't make sense to continue
                ok = FALSE;

                break;
            }

            if ( col == maskColour )
            {
                ::SetPixel(destDC, w, h, RGB(0, 0, 0));
            }
            else
            {
                ::SetPixel(destDC, w, h, RGB(255, 255, 255));
            }
        }
    }

    ::SelectObject(srcDC, hbmpSrcOld);
    ::DeleteDC(srcDC);
    ::SelectObject(destDC, hbmpDstOld);
    ::DeleteDC(destDC);

    return ok;
}

// ----------------------------------------------------------------------------
// wxBitmapHandler
// ----------------------------------------------------------------------------

bool wxBitmapHandler::Create(wxGDIImage *image,
                             void *data,
                             long flags,
                             int width, int height, int depth)
{
    wxBitmap *bitmap = wxDynamicCast(image, wxBitmap);

    return bitmap ? Create(bitmap, data, width, height, depth) : FALSE;
}

bool wxBitmapHandler::Load(wxGDIImage *image,
                           const wxString& name,
                           long flags,
                           int width, int height)
{
    wxBitmap *bitmap = wxDynamicCast(image, wxBitmap);

    return bitmap ? LoadFile(bitmap, name, flags, width, height) : FALSE;
}

bool wxBitmapHandler::Save(wxGDIImage *image,
                           const wxString& name,
                           int type)
{
    wxBitmap *bitmap = wxDynamicCast(image, wxBitmap);

    return bitmap ? SaveFile(bitmap, name, type) : FALSE;
}

bool wxBitmapHandler::Create(wxBitmap *WXUNUSED(bitmap),
                             void *WXUNUSED(data),
                             long WXUNUSED(type),
                             int WXUNUSED(width),
                             int WXUNUSED(height),
                             int WXUNUSED(depth))
{
    return FALSE;
}

bool wxBitmapHandler::LoadFile(wxBitmap *WXUNUSED(bitmap),
                               const wxString& WXUNUSED(name),
                               long WXUNUSED(type),
                               int WXUNUSED(desiredWidth),
                               int WXUNUSED(desiredHeight))
{
    return FALSE;
}

bool wxBitmapHandler::SaveFile(wxBitmap *WXUNUSED(bitmap),
                               const wxString& WXUNUSED(name),
                               int WXUNUSED(type),
                               const wxPalette *WXUNUSED(palette))
{
    return FALSE;
}

// ----------------------------------------------------------------------------
// DIB functions
// ----------------------------------------------------------------------------

bool wxCreateDIB(long xSize, long ySize, long bitsPerPixel,
                 HPALETTE hPal, LPBITMAPINFO* lpDIBHeader)
{
   unsigned long   i, headerSize;
   LPBITMAPINFO    lpDIBheader = NULL;
   LPPALETTEENTRY  lpPe = NULL;


   // Allocate space for a DIB header
   headerSize = (sizeof(BITMAPINFOHEADER) + (256 * sizeof(PALETTEENTRY)));
   lpDIBheader = (BITMAPINFO *) malloc(headerSize);
   lpPe = (PALETTEENTRY *)((BYTE*)lpDIBheader + sizeof(BITMAPINFOHEADER));

   GetPaletteEntries(hPal, 0, 256, lpPe);

   memset(lpDIBheader, 0x00, sizeof(BITMAPINFOHEADER));

   // Fill in the static parts of the DIB header
   lpDIBheader->bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
   lpDIBheader->bmiHeader.biWidth = xSize;
   lpDIBheader->bmiHeader.biHeight = ySize;
   lpDIBheader->bmiHeader.biPlanes = 1;

   // this value must be 1, 4, 8 or 24 so PixelDepth can only be
   lpDIBheader->bmiHeader.biBitCount = (WORD)(bitsPerPixel);
   lpDIBheader->bmiHeader.biCompression = BI_RGB;
   lpDIBheader->bmiHeader.biSizeImage = xSize * abs(ySize) * bitsPerPixel >> 3;
   lpDIBheader->bmiHeader.biClrUsed = 256;


   // Initialize the DIB palette
   for (i = 0; i < 256; i++) {
      lpDIBheader->bmiColors[i].rgbReserved = lpPe[i].peFlags;
      lpDIBheader->bmiColors[i].rgbRed = lpPe[i].peRed;
      lpDIBheader->bmiColors[i].rgbGreen = lpPe[i].peGreen;
      lpDIBheader->bmiColors[i].rgbBlue = lpPe[i].peBlue;
   }

   *lpDIBHeader = lpDIBheader;

   return TRUE;
}

void wxFreeDIB(LPBITMAPINFO lpDIBHeader)
{
    free(lpDIBHeader);
}

// ----------------------------------------------------------------------------
// other helper functions
// ----------------------------------------------------------------------------

extern HBITMAP wxInvertMask(HBITMAP hbmpMask, int w, int h)
{
    wxCHECK_MSG( hbmpMask, 0, _T("invalid bitmap in wxInvertMask") );

    // get width/height from the bitmap if not given
    if ( !w || !h )
    {
        BITMAP bm;
        ::GetObject(hbmpMask, sizeof(BITMAP), (LPVOID)&bm);
        w = bm.bmWidth;
        h = bm.bmHeight;
    }

    HDC hdcSrc = ::CreateCompatibleDC(NULL);
    HDC hdcDst = ::CreateCompatibleDC(NULL);
    if ( !hdcSrc || !hdcDst )
    {
        wxLogLastError(wxT("CreateCompatibleDC"));
    }

    HBITMAP hbmpInvMask = ::CreateBitmap(w, h, 1, 1, 0);
    if ( !hbmpInvMask )
    {
        wxLogLastError(wxT("CreateBitmap"));
    }

    ::SelectObject(hdcSrc, hbmpMask);
    ::SelectObject(hdcDst, hbmpInvMask);
    if ( !::BitBlt(hdcDst, 0, 0, w, h,
                   hdcSrc, 0, 0,
                   NOTSRCCOPY) )
    {
        wxLogLastError(wxT("BitBlt"));
    }

    ::DeleteDC(hdcSrc);
    ::DeleteDC(hdcDst);

    return hbmpInvMask;
}