A non-rectangular top window with click-through shadow along the edge?

unsigned char    __alphatable[256][256] = { 42, };

static void __alphatable_init()
{
  unsigned int  x,y;
  if(42==__alphatable[0][0])
  {
    for(x=0;x<256;x++)
      for(y=0;y<256;y++)
        __alphatable[x][y] = min(255,x*y/255);
  }
}

static unsigned char __alphatable_value(unsigned char src,unsigned char dst,unsigned char alpha)
{
  unsigned short p = __alphatable[alpha][src] + __alphatable[255-alpha][dst];
  return min(p,255);
}


HBITMAP __CreateAlphaBitmap(BITMAPINFO* pbmi,const unsigned char* lpbits,const unsigned int cbbits)
{
  HDC              mdc;
  HBITMAP          hbmp;
  unsigned char*  lpc;
  int              x,y;

  mdc = CreateCompatibleDC(0);
  hbmp = CreateDIBSection(mdc,pbmi,DIB_RGB_COLORS,(void**)&lpc,0,0);
  if(lpc)
  {
    __alphatable_init();
    for(y=0;y<pbmi->bmiHeader.biHeight;y++)
    {
      for(x=0;x<pbmi->bmiHeader.biWidth;x++)
      {
        lpc[0] = __alphatable_value(lpbits[0],0,lpbits[3]);
        lpc[1] = __alphatable_value(lpbits[1],0,lpbits[3]);
        lpc[2] = __alphatable_value(lpbits[2],0,lpbits[3]);
        lpc[3] = lpbits[3];
        lpc += 4; lpbits += 4;
      }
    }
  }
  DeleteDC(mdc);
  
  return hbmp;
}

void iWndWidget::SetFace(IBitmap* pBmp,HWND hwnd)
{
  if(!hwnd) return;
  
  unsigned long    exstyle = GetWindowLong(hwnd,GWL_EXSTYLE);
  BITMAPINFO*      pbmp;
  unsigned char*  lp;
  unsigned int    cb;

  if(pBmp && (S_OK==pBmp->GetBitmapDirect(&pbmp,&lp,&cb)) && (32==pbmp->bmiHeader.biBitCount))
  {
    RECT&            rcw = GetWndPos();
    BLENDFUNCTION    blend = { AC_SRC_OVER, 0, 255, AC_SRC_ALPHA };
    HDC              mdc;
    HDC              hdc = 0;
    SIZE            size = { pbmp->bmiHeader.biWidth, pbmp->bmiHeader.biHeight };
    POINT            pdst = { rcw.left,rcw.top };
    POINT            psrc = { 0,0 };
    HGDIOBJ          obmp;
    HBITMAP          hbmp;

    SetWindowLong(hwnd,GWL_EXSTYLE,exstyle|WS_EX_LAYERED);

    hbmp = __CreateAlphaBitmap(pbmp,lp,cb);
    mdc = CreateCompatibleDC(hdc);
    obmp = SelectObject(mdc,hbmp);
    UpdateLayeredWindow(hwnd,hdc,&pdst,&size,mdc,&psrc,(COLORREF)0,&blend,ULW_ALPHA);

    SelectObject(mdc,obmp);
    DeleteDC(mdc);
    DeleteObject(hbmp);

    SetWindowPos(hwnd,0,pdst.x,pdst.y,size.cx,size.cy,
      SWP_NOZORDER|SWP_FRAMECHANGED|SWP_NOSENDCHANGING|SWP_NOACTIVATE);
  }
  else
  {
    SetWindowLong(hwnd,GWL_EXSTYLE,exstyle&~WS_EX_LAYERED);
    SetWindowPos(hwnd,0,0,0,0,0,
      SWP_NOSIZE|SWP_NOMOVE|SWP_NOZORDER|SWP_FRAMECHANGED|SWP_NOSENDCHANGING|SWP_NOACTIVATE);
  }
  

}