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看龙书DX11，首先是第四章，本文对GameTime类进行解释
答：Returns the total time elapsed since Reset() was called, NOT counting any time when the clock is stopped.
从渲染窗口Reset开始记时，记录总共的时间。不包括此间的pause时间。
答：
1.
//获取频率（取决于主板 OS相关，不是CPU的主频）参考：http://www.gn00.com/t-253523-1-1.html http://www.cppblog.com/deane/articles/113151.html
BOOL QueryPerformanceFrequency(LARGE_INTEGER *lpFrequency);
//计数，在此频率下的 数值，那么(Count1-Count2)/Frequently即是此阶段的时间，以秒为单位 BOOL QueryPerformanceCounter (LARGE_INTEGER *lpCount);
2.另外一个是Pause，注意每次stop后，需要进行累加记录下来：
void GameTimer::Start() { __int64 startTime; QueryPerformanceCounter((LARGE_INTEGER*)&startTime); // Accumulate the time elapsed between stop and start pairs. // // |<-------d------->| // ----*---------------*-----------------*------------> time // mBaseTime mStopTime startTime if( mStopped ) { mPausedTime += (startTime - mStopTime); mPrevTime = startTime; mStopTime = 0; mStopped = false; } }
答：
1.在计算FPS。例子中以1S为限来进行FPS更新，计算1S内程序运行的次数。其中currentTime使用的即是gameTime.Total()接口。
void D3DApp::CalculateFrameStats() //本函数计算FPS和1S内每帧的平均时间 { //刚开始 TotalTime为0，timeElapsed也为0 static int frameCnt = 0; //然后TotalTime不断增大，直到TotalTime-timeElapsed大于1，即1S过去了，进行FPS的刷新计算 static float timeElapsed = 0.0f; frameCnt++; // Compute averages over one second period. if( (mTimer.TotalTime() - timeElapsed) >= 1.0f ) { float fps = (float)frameCnt; // fps = frameCnt / 1 float mspf = 1000.0f / fps;// Reset for next average. frameCnt = 0; timeElapsed += 1.0f; } }
2.在对win窗口的拖动、拉伸长宽、Pause时，需要调用不同记时接口。
// If user is dragging the resize bars, we do not resize the buffers here because as the user continuously drags the resize bars, a stream of WM_SIZE messages are sent to the window, and it would be pointless (and slow) to resize for each WM_SIZE message received from dragging the resize bars. So instead, we reset after the user is done resizing the window and releases the resize bars, which sends a WM_EXITSIZEMOVE message.
上文大致意思： 在不停拖动改变size时，我们并不需要resize buffer(即调用dx OnResize()接口，来重置backBuffer和depthBuffer等)，因为这样做无意义而且效率低。 所以，等 release拖动操作后，即WM_EXITSIZEMOVE 后，才进行resize和Time.Start()操作。在此之间，即WM_ENTERSIZEMOVE时，为timer.Stop()
// WM_EXITSIZEMOVE is sent when the user grabs the resize bars. case WM_ENTERSIZEMOVE: mAppPaused = true; mResizing = true; mTimer.Stop(); return 0; // WM_EXITSIZEMOVE is sent when the user releases the resize bars. // Here we reset everything based on the new window dimensions. case WM_EXITSIZEMOVE: mAppPaused = false; mResizing = false; mTimer.Start(); OnResize(); return 0;
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原文地址：http://www.cnblogs.com/dust-fly/p/4523628.html
