Mouse Gestures for Internet Explorer

///////////////////////////////////////////////////////////////
//
// GDIUtils.cpp
//
// Created: 09/07/2005
// Copyright (c) 2005 Ralph Hare (ralph.hare@ysgyfarnog.co.uk)
// All rights reserved.
//
// The code and information is provided "as-is" without
// warranty of any kind, either expressed or implied.
//
///////////////////////////////////////////////////////////////

#include "StdAfx.h"
#include "GDIUtils.h"
#include "OSUtils.h"

namespace
{
//
// Wrapper around the SetLayeredWindowAttributes API. Rather than statically
// linking to it, we dynamically link so that MouseGestures.dll will load
// on NT4 and the like, but the mouse trails will be disabled
//
    class LayerHelper
    {
    public:
        LayerHelper() :
            m_hMod( ::LoadLibrary( _T( "User32.dll" ) ) ),
            m_pfn( NULL )
        {
            m_pfn = reinterpret_cast< SLWA_PROC * >( ::GetProcAddress( m_hMod, "SetLayeredWindowAttributes" ) );
        }

        ~LayerHelper()
        {
            ::FreeLibrary( m_hMod );
        }

        BOOL __stdcall SetLayeredWindowAttribute( HWND hWnd, COLORREF crKey, BYTE bAlpha, DWORD dwFlags )
        {
            if( m_pfn )
            {
                return ( *m_pfn )( hWnd, crKey, bAlpha, dwFlags );
            }

            return FALSE;
        }

    private:
        typedef BOOL ( __stdcall SLWA_PROC )( HWND, COLORREF, BYTE, DWORD );

    private:
        HMODULE     m_hMod;
        SLWA_PROC   *m_pfn;
    };
}

namespace GDIUtils
{
    BOOL __stdcall SetLayeredWindowAttribute( HWND hWnd, COLORREF crKey, BYTE bAlpha, DWORD dwFlags )
    {
        if( OSUtils::IsNT4() )
        {
            return TRUE;
        }

        static LayerHelper  lh;
        return lh.SetLayeredWindowAttribute( hWnd, crKey, bAlpha, dwFlags );
    }
}