首先看骨骼追踪例子代码的结构：
例子代码不是很多，在SkeletonBasics.cpp中，大部分的功能都在kinect SDK中实现，应用开发只需要了解接口，并调用它的接口即可。首先我们找到main函数：
int APIENTRY wWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPWSTR lpCmdLine, int nCmdShow)
{
CSkeletonBasics application;
application.Run(hInstance, nCmdShow);
}
这个main函数是不是似曾相识，跟深度图的main函数差不多的，只是构造一个对象，然后调用这个对象的Run接口，构造函数只是初始化成员，所以我们直接看Run的实现：
int CSkeletonBasics::Run(HINSTANCE hInstance, int nCmdShow)
{
MSG msg = {0};
WNDCLASS wc = {0};
// Dialog custom window class
wc.style = CS_HREDRAW | CS_VREDRAW;
wc.cbWndExtra = DLGWINDOWEXTRA;
wc.hInstance = hInstance;
wc.hCursor = LoadCursorW(NULL, IDC_ARROW);
wc.hIcon = LoadIconW(hInstance, MAKEINTRESOURCE(IDI_APP));
wc.lpfnWndProc = DefDlgProcW;
wc.lpszClassName = L"SkeletonBasicsAppDlgWndClass";
if (!RegisterClassW(&wc))
{
return 0;
}
// Create main application window
HWND hWndApp = CreateDialogParamW(
hInstance,
MAKEINTRESOURCE(IDD_APP),
NULL,
(DLGPROC)CSkeletonBasics::MessageRouter,
reinterpret_cast<LPARAM>(this));
// Show window
ShowWindow(hWndApp, nCmdShow);
const int eventCount = 1;
HANDLE hEvents[eventCount];
// Main message loop
while (WM_QUIT != msg.message)
{
hEvents[0] = m_hNextSkeletonEvent;
// Check to see if we have either a message (by passing in QS_ALLEVENTS)
// Or a Kinect event (hEvents)
// Update() will check for Kinect events individually, in case more than one are signalled
DWORD dwEvent = MsgWaitForMultipleObjects(eventCount, hEvents, FALSE, INFINITE, QS_ALLINPUT);
// Check if this is an event we're waiting on and not a timeout or message
if (WAIT_OBJECT_0 == dwEvent)
{
Update();
}
if (PeekMessageW(&msg, NULL, 0, 0, PM_REMOVE))
{
// If a dialog message will be taken care of by the dialog proc
if ((hWndApp != NULL) && IsDialogMessageW(hWndApp, &msg))
{
continue;
}
TranslateMessage(&msg);
DispatchMessageW(&msg);
}
}
return static_cast<int>(msg.wParam);
}
这个Run函数是不是也是很熟悉，跟深度图的Run函数也是差不多，创建对话框，然后进入消息处理死循环，在死循环里处理窗口消息和kinect消息。
接下来和深度图一样，我们也进入到窗口初始化消息里，看整个程序的初始化是怎么样的：
LRESULT CALLBACK CSkeletonBasics::DlgProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
switch (message)
{
case WM_INITDIALOG:
{
// Bind application window handle
m_hWnd = hWnd;
// Init Direct2D
D2D1CreateFactory(D2D1_FACTORY_TYPE_SINGLE_THREADED, &m_pD2DFactory);
// Look for a connected Kinect, and create it if found
CreateFirstConnected();
}
break;
初始化处理和深度图也差不多，D2D1CreateFactory函数创建DirectX对象，然后调用CreateFirstConnected去创建kinect对象，在CreateFirstConnected函数里的处理又有何不同呢？我们一起来看代码：
HRESULT CSkeletonBasics::CreateFirstConnected()
{
INuiSensor * pNuiSensor;
// 获取kinect数量
int iSensorCount = 0;
HRESULT hr = NuiGetSensorCount(&iSensorCount);
if (FAILED(hr))
{
return hr;
}
// Look at each Kinect sensor 查找一个有效的kinect设备
for (int i = 0; i < iSensorCount; ++i)
{
// Create the sensor so we can check status, if we can't create it, move on to the next
hr = NuiCreateSensorByIndex(i, &pNuiSensor);
if (FAILED(hr))
{
continue;
}
// Get the status of the sensor, and if connected, then we can initialize it
hr = pNuiSensor->NuiStatus();
if (S_OK == hr)
{
m_pNuiSensor = pNuiSensor;
break;
}
// This sensor wasn't OK, so release it since we're not using it
pNuiSensor->Release();
}
if (NULL != m_pNuiSensor)
{
// 这里的参数和深度图不一样，深度图用的参数是NUI_INITIALIZE_FLAG_USES_DEPTH
// 这个意思就是将这个kinect初始化成骨骼跟踪
hr = m_pNuiSensor->NuiInitialize(NUI_INITIALIZE_FLAG_USES_SKELETON);
if (SUCCEEDED(hr))
{
// 这个Event和深度图一样，是kinectSDK和上层应用程序通信的事件
m_hNextSkeletonEvent = CreateEventW(NULL, TRUE, FALSE, NULL);
// 打开一个骨骼跟踪数据，深度图需要的参数比较复杂，这个比较简答
hr = m_pNuiSensor->NuiSkeletonTrackingEnable(m_hNextSkeletonEvent, 0);
}
}
if (NULL == m_pNuiSensor || FAILED(hr))
{
SetStatusMessage(L"No ready Kinect found!");
return E_FAIL;
}
return hr;
}
看初始化kinect设备的代码，貌似区别也不是很大，只是初始化参数不同，打开数据流的函数不同，框架性的代码还是差不多的。
当这个m_hNextSkeletonEvent事件被注册到kinect SDK库之后，当有数据来时，Update函数会被调用，Update函数最后调用了ProcessSkeleton函数来处理骨骼数据：
void CSkeletonBasics::ProcessSkeleton()
{
NUI_SKELETON_FRAME skeletonFrame = {0};
// 获取一帧骨骼数据
HRESULT hr = m_pNuiSensor->NuiSkeletonGetNextFrame(0, &skeletonFrame);
if ( FAILED(hr) )
{
return;
}
// 让骨骼数据变得平滑，消除抖动现象
m_pNuiSensor->NuiTransformSmooth(&skeletonFrame, NULL);
// 创建m_pRenderTarget对象
hr = EnsureDirect2DResources( );
if ( FAILED(hr) )
{
return;
}
m_pRenderTarget->BeginDraw();
m_pRenderTarget->Clear( );
RECT rct;
GetClientRect( GetDlgItem( m_hWnd, IDC_VIDEOVIEW ), &rct);
int width = rct.right;
int height = rct.bottom;
// 最多支持6个人的骨骼跟踪数据
for (int i = 0 ; i < NUI_SKELETON_COUNT; ++i)
{
NUI_SKELETON_TRACKING_STATE trackingState = skeletonFrame.SkeletonData[i].eTrackingState;
if (NUI_SKELETON_TRACKED == trackingState)
{
// 画骨骼
DrawSkeleton(skeletonFrame.SkeletonData[i], width, height);
}
else if (NUI_SKELETON_POSITION_ONLY == trackingState)
{
// 只是跟踪位置的话，那么就画个位置，在人很多时，kinect只跟踪两个人的骨骼，其他人之显示位置
D2D1_ELLIPSE ellipse = D2D1::Ellipse(
SkeletonToScreen(skeletonFrame.SkeletonData[i].Position, width, height),
g_JointThickness,
g_JointThickness
);
m_pRenderTarget->DrawEllipse(ellipse, m_pBrushJointTracked);
}
}
hr = m_pRenderTarget->EndDraw();
// Device lost, need to recreate the render target
// We'll dispose it now and retry drawing
if (D2DERR_RECREATE_TARGET == hr)
{
hr = S_OK;
DiscardDirect2DResources();
}
}
在处理骨骼数据函数中，对数据skeletonFrame中保存的六个骨骼跟踪数据循环处理，如果状态是NUI_SKELETON_TRACKED则通过DrawSkeleton画详细骨骼信息，如果是NUI_SKELETON_POSITION_ONLY则只画位置信息，如果不是这两个状态，则啥也不做。接下来我们来看看DrawSkeleton看看骨骼信息怎么画的：
void CSkeletonBasics::DrawSkeleton(const NUI_SKELETON_DATA & skel, int windowWidth, int windowHeight)
{
int i;
// 将关节点转化成屏幕上的坐标点
for (i = 0; i < NUI_SKELETON_POSITION_COUNT; ++i)
{
m_Points[i] = SkeletonToScreen(skel.SkeletonPositions[i], windowWidth, windowHeight);
}
// 画骨骼，参数1是骨骼数据，参数2和参数3是关节
DrawBone(skel, NUI_SKELETON_POSITION_HEAD, NUI_SKELETON_POSITION_SHOULDER_CENTER); // 这个是脑袋，从脑袋关节到肩膀中间
DrawBone(skel, NUI_SKELETON_POSITION_SHOULDER_CENTER, NUI_SKELETON_POSITION_SHOULDER_LEFT); // 肩膀中间到左边
DrawBone(skel, NUI_SKELETON_POSITION_SHOULDER_CENTER, NUI_SKELETON_POSITION_SHOULDER_RIGHT); // 肩膀中间到右边，下面的类似
DrawBone(skel, NUI_SKELETON_POSITION_SHOULDER_CENTER, NUI_SKELETON_POSITION_SPINE);
DrawBone(skel, NUI_SKELETON_POSITION_SPINE, NUI_SKELETON_POSITION_HIP_CENTER);
DrawBone(skel, NUI_SKELETON_POSITION_HIP_CENTER, NUI_SKELETON_POSITION_HIP_LEFT);
DrawBone(skel, NUI_SKELETON_POSITION_HIP_CENTER, NUI_SKELETON_POSITION_HIP_RIGHT);
// Left Arm
DrawBone(skel, NUI_SKELETON_POSITION_SHOULDER_LEFT, NUI_SKELETON_POSITION_ELBOW_LEFT);
DrawBone(skel, NUI_SKELETON_POSITION_ELBOW_LEFT, NUI_SKELETON_POSITION_WRIST_LEFT);
DrawBone(skel, NUI_SKELETON_POSITION_WRIST_LEFT, NUI_SKELETON_POSITION_HAND_LEFT);
// Right Arm
DrawBone(skel, NUI_SKELETON_POSITION_SHOULDER_RIGHT, NUI_SKELETON_POSITION_ELBOW_RIGHT);
DrawBone(skel, NUI_SKELETON_POSITION_ELBOW_RIGHT, NUI_SKELETON_POSITION_WRIST_RIGHT);
DrawBone(skel, NUI_SKELETON_POSITION_WRIST_RIGHT, NUI_SKELETON_POSITION_HAND_RIGHT);
// Left Leg
DrawBone(skel, NUI_SKELETON_POSITION_HIP_LEFT, NUI_SKELETON_POSITION_KNEE_LEFT);
DrawBone(skel, NUI_SKELETON_POSITION_KNEE_LEFT, NUI_SKELETON_POSITION_ANKLE_LEFT);
DrawBone(skel, NUI_SKELETON_POSITION_ANKLE_LEFT, NUI_SKELETON_POSITION_FOOT_LEFT);
// Right Leg
DrawBone(skel, NUI_SKELETON_POSITION_HIP_RIGHT, NUI_SKELETON_POSITION_KNEE_RIGHT);
DrawBone(skel, NUI_SKELETON_POSITION_KNEE_RIGHT, NUI_SKELETON_POSITION_ANKLE_RIGHT);
DrawBone(skel, NUI_SKELETON_POSITION_ANKLE_RIGHT, NUI_SKELETON_POSITION_FOOT_RIGHT);
// 画关节
for (i = 0; i < NUI_SKELETON_POSITION_COUNT; ++i)
{
D2D1_ELLIPSE ellipse = D2D1::Ellipse( m_Points[i], g_JointThickness, g_JointThickness );
if ( skel.eSkeletonPositionTrackingState[i] == NUI_SKELETON_POSITION_INFERRED )
{
m_pRenderTarget->DrawEllipse(ellipse, m_pBrushJointInferred);
}
else if ( skel.eSkeletonPositionTrackingState[i] == NUI_SKELETON_POSITION_TRACKED )
{
m_pRenderTarget->DrawEllipse(ellipse, m_pBrushJointTracked);
}
}
}
在这里绘制比较简单，所以这里绘制并没有像深度图一样使用一个类来做绘制，直接写到函数里了。另外一个这里DirectX的绘制也就只是画画线，如果你熟悉GDI，完全可以通过GDI来绘图，而不用DirectX。