PNG 异形对话框 图片位深度的疑问！！！

void CPNGDlg::UpdateView(CString pngFileName, int width,int height)
{
HBITMAP hBitmap;
hBitmap=CreateCompatibleBitmap(this->GetDC()->m_hDC,width,height);
hBitmap=ConverBmp(hBitmap);
m_bmpDialog.DeleteObject();
m_bmpDialog.Attach(hBitmap); DoUpdateDummyDialog(pngFileName, *this,m_bmpDialog,255);
}
void CPNGDlg::DoUpdateDummyDialog(CString pngFileName, CWnd &wnd, CBitmap &bmp, BYTE SourceConstantAlpha)
{
CBitmap *pOldBitmap= dcMemory.SelectObject(&bmp);
BITMAP bmpInfo;
bmp.GetBitmap(&bmpInfo);
CRect rectDlg;
wnd.GetWindowRect(rectDlg);
CPoint ptWindowScreenPosition(rectDlg.TopLeft());
CSize szWindow(bmpInfo.bmWidth, bmpInfo.bmHeight);
BLENDFUNCTION blendPixelFunction= { AC_SRC_OVER, 0, SourceConstantAlpha, 0x01};
CPoint ptSrc(0,0); Graphics graphics(dcMemory.m_hDC); ////////////////////////////////////////////////////////////////////////// Bitmap *m_bit=new Bitmap(pngFileName.AllocSysString());
graphics.DrawImage(m_bit,0,0);
delete m_bit; ////////////////////////////////////////////////////////////////////////// graphics.ReleaseHDC(dcMemory.m_hDC); HINSTANCE hInst=::LoadLibrary("user32.dll");    
if (hInst)    
{    
typedef BOOL (WINAPI *MYFUNC)(HWND,HDC,POINT*,SIZE*,HDC,POINT*,COLORREF,BLENDFUNCTION*,DWORD);    
MYFUNC fun=NULL;    fun=(MYFUNC)GetProcAddress(hInst,"UpdateLayeredWindow");  
if (fun)
fun(wnd,m_screenDC->m_hDC, &ptWindowScreenPosition, &szWindow, dcMemory,&ptSrc, 0, &blendPixelFunction, 0x02);     FreeLibrary(hInst);    
} dcMemory.SelectObject(pOldBitmap);
}
HBITMAP CPNGDlg::ConverBmp(HBITMAP hBitmap)
{
HDC hDC;
WORD wBitCount=32;
DWORD dwPaletteSize=0, dwBmBitsSize=0, dwDIBSize=0, dwWritten=0;
BITMAP Bitmap; 
BITMAPINFOHEADER bi; 
LPBITMAPINFOHEADER lpbi; 
HANDLE hPal,hOldPal=NULL;
HBITMAP hDib; GetObject(hBitmap, sizeof(Bitmap), (LPSTR)&Bitmap);
bi.biSize = sizeof(BITMAPINFOHEADER);
bi.biWidth = Bitmap.bmWidth;
bi.biHeight = Bitmap.bmHeight;
bi.biPlanes = 1;
bi.biBitCount = wBitCount;
bi.biCompression = BI_RGB;
bi.biSizeImage = 0;
bi.biXPelsPerMeter = 0;
bi.biYPelsPerMeter = 0;
bi.biClrImportant = 0;
bi.biClrUsed = 0; dwBmBitsSize = ((Bitmap.bmWidth * wBitCount + 31) / 32) * 4 * Bitmap.bmHeight; hPal = GetStockObject(DEFAULT_PALETTE);
if (hPal)
{
hDC = ::GetDC(NULL);
hOldPal = ::SelectPalette(hDC, (HPALETTE)hPal, FALSE);
RealizePalette(hDC);
} hDib = CreateDIBSection(hDC,(BITMAPINFO*)&bi,DIB_RGB_COLORS, (LPVOID*)&lpbi, NULL, 0);
GetDIBits(hDC, hBitmap, 0, (UINT) Bitmap.bmHeight, (LPSTR)lpbi+dwPaletteSize, (LPBITMAPINFO)&bi, DIB_RGB_COLORS);
if (hOldPal)
{
::SelectPalette(hDC, (HPALETTE)hOldPal, TRUE);
RealizePalette(hDC);
::ReleaseDC(NULL, hDC);
} CloseHandle(hPal);
CloseHandle(hOldPal);
DeleteObject(hBitmap); return hDib;
}BOOL CPNGDlg::OnInitDialog()
{
CDialog::OnInitDialog(); // TODO:  在此添加额外的初始化
m_screenDC=new CDC();
m_screenDC->Attach(::GetDC(NULL));
dcMemory.CreateCompatibleDC(m_screenDC);
ModifyStyleEx(0,0x80000); CString m_AppPath;
char szPathName[MAX_PATH];
::GetModuleFileName(NULL,szPathName,sizeof(szPathName));
m_AppPath=CString(szPathName).Left(CString(szPathName).ReverseFind('//')+1); UpdateView(_T("res\\bg.png"),595,396); return TRUE;  // return TRUE unless you set the focus to a control
// 异常: OCX 属性页应返回 FALSE
}
这段代码是支持24位PNG图片的异性窗口，但是当我加载32位PNG图片的时候，图片会变大，失真很多，请教大家如何将代码修改为支持32位PNG图片异性窗口！感谢！！！