C / C++ / MFC

	this->ModifyStyleEx(0, WS_EX_LAYERED);

//---- Generate 32bpp bitmap
	BITMAPINFO bmi;
	memset(&bmi, 0, sizeof(BITMAPINFO));
	bmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
	bmi.bmiHeader.biPlanes = 1;
	bmi.bmiHeader.biWidth = 255;
	bmi.bmiHeader.biHeight = 255;
	bmi.bmiHeader.biBitCount = 32;

	unsigned char* bits;

	HDC hdc = CreateCompatibleDC(::GetDC(0));
	HBITMAP hbmp = CreateDIBSection(hdc, &bmi, DIB_RGB_COLORS, (void**)&bits, 0, 0);
	SelectObject(hdc, (HBITMAP)hbmp);
	
	char alp = 0;
	for (int j=0; j<255; j++){
		unsigned char* vertbits = bits + j*255*4;
		for (int i=0; i<255*4; i+=4){
			vertbits[i+0] = 255 * alp / 255;
			vertbits[i+1] = 0;
			vertbits[i+2] = 255 * alp / 255;
			vertbits[i+3] = alp;
			alp++; alp%=256;
		}
	}
//----


	BLENDFUNCTION bf = {AC_SRC_OVER, 0, 255, AC_SRC_ALPHA};
	SIZE s = {255,255};
	POINT p = {0,0};
	BOOL res = ::UpdateLayeredWindow(m_hWnd, ::GetDC(0), 0, &s, hdc, &p, 0, &bf, ULW_ALPHA); //<-- ERROR HERE
	//AlphaBlend(GetDC()->m_hDC, 0, 0, 255, 255, hdc, 0,0,255,255,bf );

OnDrawItem(int nIDCtl, LPDRAWITEMSTRUCT lpDrawItemStruct)<br />
{<br />
CDialog::OnDrawItem(nIDCtl, lpDrawItemStruct);<br />
<br />
HDC thdc = CreateCompatibleDC(lpDrawItemStruct->hDC);<br />
HGDIOBJ tobj = SelectObject(thdc, LoadBitmap(AfxGetInstanceHandle(), MAKEINTRESOURCE(IDB_ARROW_DOWN)));<br />
TransparentBlt(lpDrawItemStruct->hDC, lpDrawItemStruct->rcItem.right - 20, lpDrawItemStruct->rcItem.top + (lpDrawItemStruct->rcItem.bottom - lpDrawItemStruct->rcItem.top - 16) / 2, 16, 16, thdc, 0, 0, 16, 16, RGB(255, 0, 255));<br />
SelectObject(thdc, tobj);<br />
DeleteDC(thdc);<br />
}