HTC Touch Pro带的重力感应功能很实用，不过一直在寻思能否找到重力感应器的SDK。在网上搜罗了一大圈，都没结果，看来厂商并不希望公开这样的接口。果不其然，在一个国外的网站上，发现了一篇有趣的文章：
http://scottandmichelle.net/scott/comments.html?entry=784
I spent a couple of sleepless hours last night writing a little Sensor Test for my new HTC Diamond. It’s a small app that lets you move a circle around the screen by tilting the device.
Exciting, eh? Well, the fun is in getting it to work. I asked HTC if they provide a development kit (SDK) for the tilt sensor, and they said “No”, so I had to figure it out myself by digging around (and trying to remember what I knew of ARM assembly). I’m just happy I managed to figure it out, and so others can write interesting games with it, I’m giving the source code to what I figured out away. Have fun, create something with it.
相当搞笑，这位哥们本来打算要求HTC提供这样的SDK开发包，想不到被HTC无情的拒绝了，于是一怒之下，把重力感应相关的库文件给反向工程了，并公开了源码。这下可好了，咱们可以开动大脑，设计更多的和重力相关的有趣的应用了。研究了这位外国哥们的代码，重力感应器相关的API，主要包含在一个叫做”HTCSensorSDK.dll”的动态库里面，该动态库主要输出的两个函数分别是：HTCSensorOpen和HTCSensorClose ，用于打开重力感应器和关闭重力感应器。当重力感应器打开之后，可以对手机当前位置的变化进行监视，其实是通过检测注册表的某个键值实现的，具体的路径在Software\HTC\HTCSensor\GSensor的EventChanged。在打开重力感应器的情况下，当这个键的值发生变化，意味着手机的位置已经发生了变动。手机位置的定义包括六种情况，以地平线位置作为参考，可分为：手机正面(屏幕)向上、手机正面(屏幕)向下、手机正面(屏幕)向左、手机正面(屏幕)向右、手机正面(屏幕)向前、手机正面(屏幕)向后。而这六种位置在注册表键EventChanged中均有不同的值表示。
为了方便应用，我将开启/关闭 重力感应器的代码抽取了出来，做成一个动态连接库，暴露的接口如下：
<span class="lnum"> 1: </span><span class="kwrd">extern</span> <span class="str">"C"</span> __declspec(dllexport) BOOL EnableGSensor();
<span class="lnum"> 2: </span><span class="kwrd">extern</span> <span class="str">"C"</span> __declspec(dllexport) BOOL DisableGSensor();
这样就能方便的开启和关闭重力感应器了。
下面就可以用简单的MFC Dialog程序来测试重力感应了：
定义注册表路径和被监视的键值
<span class="lnum"> 1: </span><span class="preproc">#define</span> SN_GSENSOR_ROOT HKEY_LOCAL_MACHINE
<span class="lnum"> 2: </span><span class="preproc">#define</span> SN_GSENSOR_PATH _T(<span class="str">"Software\\HTC\\HTCSensor\\GSensor"</span>)
<span class="lnum"> 3: </span><span class="preproc">#define</span> SN_GSENSOR_VALUE _T(<span class="str">"EventChanged"</span>)
定义注册表值掩码，以及6个不同位置的值
<span class="lnum"> 1: </span><span class="preproc">#define</span> SN_GSENSOR_BITMASK 0xF
<span class="lnum"> 2: </span>
<span class="lnum"> 3: </span><span class="preproc">#define</span> orIENTATION_LANDSCAPE 0
<span class="lnum"> 4: </span><span class="preproc">#define</span> orIENTATION_REVERSE_LANDSCAPE 1
<span class="lnum"> 5: </span><span class="preproc">#define</span> orIENTATION_PORTRAIT 2
<span class="lnum"> 6: </span><span class="preproc">#define</span> orIENTATION_UPSIDE_DOWN 3
<span class="lnum"> 7: </span><span class="preproc">#define</span> orIENTATION_FACE_DOWN 4
<span class="lnum"> 8: </span><span class="preproc">#define</span> orIENTATION_FACE_UP 5
定义注册表值变化的Windows Message类型
<span class="lnum"> 1: </span><span class="preproc">#define</span> WM_EVENTCHANGED (WM_USER + 1)
在消息映射宏中，定义响应自定义消息WM_EVENTCHANGED的处理函数
<span class="lnum"> 1: </span>ON_MESSAGE(WM_EVENTCHANGED,OnEventChanged)
这样，我们就可以在Dialog程序的初始化函数里面实现相应的代码：
<span class="lnum"> 1: </span>BOOL CTestDlg::OnInitDialog()
<span class="lnum"> 2: </span>{
<span class="lnum"> 3: </span> CDialog::OnInitDialog();
<span class="lnum"> 4: </span>
<span class="lnum"> 5: </span> <span class="rem">// Set the icon for this dialog. The framework does this automatically</span>
<span class="lnum"> 6: </span> <span class="rem">// when the application's main window is not a dialog</span>
<span class="lnum"> 7: </span> SetIcon(m_hIcon, TRUE); <span class="rem">// Set big icon</span>
<span class="lnum"> 8: </span> SetIcon(m_hIcon, FALSE); <span class="rem">// Set small icon</span>
<span class="lnum"> 9: </span>
<span class="lnum"> 10: </span> <span class="rem">// TODO: Add extra initialization here</span>
<span class="lnum"> 11: </span> g_hSensorEvent = NULL;
<span class="lnum"> 12: </span>
<span class="lnum"> 13: </span> RegistryNotifyWindow(
<span class="lnum"> 14: </span> SN_GSENSOR_ROOT,
<span class="lnum"> 15: </span> SN_GSENSOR_PATH,
<span class="lnum"> 16: </span> SN_GSENSOR_VALUE,
<span class="lnum"> 17: </span> GetSafeHwnd(),
<span class="lnum"> 18: </span> WM_EVENTCHANGED,
<span class="lnum"> 19: </span> SN_GSENSOR,
<span class="lnum"> 20: </span> NULL,
<span class="lnum"> 21: </span> &g;_hSensorEvent);
<span class="lnum"> 22: </span>
<span class="lnum"> 23: </span> gSensorWrapper.EnableGSensor();
<span class="lnum"> 24: </span>
<span class="lnum"> 25: </span> <span class="kwrd">return</span> TRUE; <span class="rem">// return TRUE unless you set the focus to a control</span>
<span class="lnum"> 26: </span>}
RegistryNotifyWindow函数，通过监视注册表的指定路径下，指定键值的变化，向我们的窗口发送WM_EVENTCHANGED消息，而我们在消息映射宏中所定义的OnEventChanged函数，就用来响应和处理这样的自定义消息。
最后，在我们的OnEventChanged函数中，就可以获得当前手机的位置了：
<span class="lnum"> 1: </span>afx_msg LRESULT CHangupPhoneDlg::OnEventChanged(WPARAM wParam, LPARAM lParam)
<span class="lnum"> 2: </span>{
<span class="lnum"> 3: </span> nLastEvent = (wParam & SN_GSENSOR_BITMASK);
<span class="lnum"> 4: </span>
<span class="lnum"> 5: </span> <span class="kwrd">switch</span> (nLastEvent)
<span class="lnum"> 6: </span> {
<span class="lnum"> 7: </span> <span class="kwrd">case</span> orIENTATION_LANDSCAPE:
<span class="lnum"> 8: </span> szMessage = _T(<span class="str">"Last Event: 正面向右"</span>);
<span class="lnum"> 9: </span> <span class="kwrd">break</span>;
<span class="lnum"> 10: </span> <span class="kwrd">case</span> orIENTATION_REVERSE_LANDSCAPE:
<span class="lnum"> 11: </span> szMessage = _T(<span class="str">"Last Event: 正面向左"</span>);
<span class="lnum"> 12: </span> <span class="kwrd">break</span>;
<span class="lnum"> 13: </span> <span class="kwrd">case</span> orIENTATION_PORTRAIT:
<span class="lnum"> 14: </span> szMessage = _T(<span class="str">"Last Event: 正面向后"</span>);
<span class="lnum"> 15: </span> <span class="kwrd">break</span>;
<span class="lnum"> 16: </span> <span class="kwrd">case</span> orIENTATION_UPSIDE_DOWN:
<span class="lnum"> 17: </span> szMessage = _T(<span class="str">"Last Event: 正面向前"</span>);
<span class="lnum"> 18: </span> <span class="kwrd">break</span>;
<span class="lnum"> 19: </span> <span class="kwrd">case</span> orIENTATION_FACE_DOWN:
<span class="lnum"> 20: </span> szMessage = _T(<span class="str">"Last Event: 正面向下"</span>);
<span class="lnum"> 21: </span> <span class="kwrd">break</span>;
<span class="lnum"> 22: </span> <span class="kwrd">case</span> orIENTATION_FACE_UP:
<span class="lnum"> 23: </span> szMessage = _T(<span class="str">"Last Event: 正面向上"</span>);
<span class="lnum"> 24: </span> <span class="kwrd">break</span>;
<span class="lnum"> 25: </span> <span class="kwrd">default</span>:
<span class="lnum"> 26: </span> szMessage = _T(<span class="str">"Last Event: Unknown"</span>);
<span class="lnum"> 27: </span> <span class="kwrd">break</span>;
<span class="lnum"> 28: </span> }
<span class="lnum"> 29: </span>
<span class="lnum"> 30: </span> <span class="kwrd">this</span>->GetDlgItem(IDC_DISPLAY)->SetWindowTextW(szMessage);
<span class="lnum"> 31: </span>
<span class="lnum"> 32: </span>
<span class="lnum"> 33: </span> <span class="kwrd">return</span> 0L;
<span class="lnum"> 34: </span>}
启动测试程序，翻转手机到不同的位置，就能在Dialog框中，实时看到当前手机位置状态，Cool!
测试程序比较简单，就不放上来了，把封装的重力感应器的动态库放上来，供有兴趣的同学下载。
可以进行测试的手机型号：多普达(Dopod) Touch Diamond、多普达(Dopod) Touch Pro 或者 HTC Touch Diamond 和 HTC Touch Pro.
我的开发测试环境： Windows Vista 64bit, Visual Studio 2008 SP1, Windows Mobile 6.0 Professional SDK.
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