CDC::BitBlt problem

  
//grab a dc compatible with the desktop dc

CClientDC* pDeskCDC=new CClientDC(NULL);

//and another one to blit to (to store for WM_PAINT)

pDC=new CDC;
pDC->CreateCompatibleDC(NULL);
//get dimensions of this dialog so we get the right part of

//the desktop window

RECT Rect;
GetWindowRect(&Rect);

int xPos=Rect.left;
int yPos=Rect.top;
int iWidth=Rect.right-xPos;
int iHeight=Rect.bottom-yPos;
//blit the rect specified above from the dekstop to

//my memory dc to be used in OnPaint

pDC->BitBlt(0,0,iWidth,iHeight,pDeskCDC,xPos,yPos,SRCCOPY);

//test that it has actually copied it

for(int y=0;y<iHeight;y++)
{
	for(int x=0;x<iWidth;x++)
	{
                //find color of pixels in memory dc

		COLORREF color=pDC->GetPixel(x,y);

		DWORD Red=GetRValue(color);
		DWORD Green=GetGValue(color);
		DWORD Blue=GetBValue(color);

                //find color of pixels in desktrop dc

                //i.e. the color the above pixels should be

		color=pDeskCDC->GetPixel(x,y);

		Red=GetRValue(color);
		Green=GetGValue(color);
		Blue=GetBValue(color);
	}
}