Drawing an item from an Image List with a drop shadow

void DrawImageListItem(CDC *pDC, int x, int y,
                    CImageList *piml, int nImage, bool bDropShadow)
{
    if (bDropShadow)
    {
        // This is quite simple:
        // We draw the mask in COLOR_3DSHADOW, offset slightly
        // down & right.
        // We draw the item transparently, offset slightly
        // up & left.

        // We need to know how big each item in the image list is:
        int cx, cy;
        ImageList_GetIconSize(piml->GetSafeHandle(), &cx, &cy);

        // Drawing the drop shadow in the appropriate colour is trickier:
        // we need to go via a memory DC.
        
        // We need a memory DC, backed with some bits.
        CDC memoryDC;
        VERIFY(memoryDC.CreateCompatibleDC(pDC));
        CBitmap memoryBitmap;
        VERIFY(memoryBitmap.CreateCompatibleBitmap(pDC, cx, cy));
        CBitmap *oldMemoryBitmap = memoryDC.SelectObject(&memoryBitmap);

        // Draw the mask onto it.
        // Transparent parts of the image are white.
        // Opaque parts are black.
        piml->Draw(&memoryDC, nImage, CPoint(0, 0), ILD_MASK);

        // This raster code does the necessary magic:
        // Where there's a black pixel in the source DC,
        // use the current brush.
        // Where there's a white pixels leave the destination alone.
        const DWORD CP_ROP = 0xB8074A;

        // So, we need a brush:
        CBrush br;
        br.CreateSolidBrush(GetSysColor(COLOR_3DSHADOW));

        // Do the magic
        CBrush *oldBrush = pDC->SelectObject(&br);
        pDC->BitBlt(x + 1, y, cx, cy, &memoryDC, 0, 0, CP_ROP);
        pDC->SelectObject(oldBrush);

        // Start cleaning up.
        memoryDC.SelectObject(oldMemoryBitmap);

        // That's given us a drop shadow.
        // All we need to do now is put the normal image over the top.
        piml->Draw(pDC, nImage, CPoint(x-1, y-1),
                        ILD_NORMAL | ILD_TRANSPARENT);
    }
    else
    {
        // Then it's much, much simpler: just get the
        // image list to draw on the DC directly.
        piml->Draw(pDC, nImage, CPoint(x,y),
                        ILD_NORMAL | ILD_TRANSPARENT);
    }
}