我正在使用visual studio 2012,想了解high_resolution_clock的准确性。
基本上我会编写一些代码来显示声音和图像,但是我需要它们才能很好地同步,并且图像必须是无泪的。我使用directX来提供无泪图像,并使用high_resolution_clock进行计时屏幕刷新。显示器声称为60 fps,然而,使用high_resolution_clock的时序提供60.035 fps的刷新率,平均超过10000次屏幕刷新。根据哪个是正确的,我的音频将在一秒钟后以0.5毫秒结束,一小时后约为2秒。我希望任何时钟都比这更准确 - 更像是一年内漂移,而不是一小时。
以前有没有人看过这种东西。我应该期待我的声卡时钟再次不同吗?
编辑 这是我的计时代码。这个while循环在我的渲染线程中运行。 m_renderData是包含渲染场景所需数据的结构数组,每个屏幕有一个元素。对于测试我只在一个屏幕上运行,因此它只有一个元素
while(!TestDestroy())
{
for(size_t i=0; i<m_renderData.size(); ++i)
{
//work out where in the vsync cycle we are and increment the render cycle
//as needed until we need to actually render
D3DRASTER_STATUS rStatus;
m_renderData[i].deviceD3D9->GetRasterStatus(0, &rStatus);
if(m_renderData[i].renderStage==inVBlankRenderingComplete)
{
if(!rStatus.InVBlank)
m_renderData[i].renderStage=notInVBlank;
}
else if(m_renderData[i].renderStage==notInVBlank)
{
if(rStatus.InVBlank)
m_renderData[i].renderStage=inVBlankReadyToRender;
}
//check for missing the vsync for rendering
bool timeOut=false;
if(m_renderData[i].durations.size()>0)
{
double timeSinceLastRender=std::chrono::duration_cast<std::chrono::microseconds>(std::chrono::high_resolution_clock::now()-m_renderData[i].durations.back()).count();
if (timeSinceLastRender>expectedUpdatePeriod*1.2)
timeOut=true;
}
if(m_renderData[i].renderStage==inVBlankReadyToRender || timeOut)
{
//We have reached the time to render
//record the time and increment the number of renders that have been performed
m_renderData[i].durations.push_back(std::chrono::high_resolution_clock::now());
++m_renderData[i].nRenders;
//we calculate the fps using 10001 times - i.e. an interval of 10000 frames
size_t fpsUpdatePeriod=10001;
if(m_renderData[i].nRenders<fpsUpdatePeriod)
{
//if we don't have enough times then display a message
m_renderData[i].fpsString = "FPS: Calculating";
}
else
{
//we have enough timing info, calculate the fps
double meanFrameTime = std::chrono::duration_cast<std::chrono::microseconds>(m_renderData[i].durations.back()-*(m_renderData[i].durations.end()-fpsUpdatePeriod)).count()/double(fpsUpdatePeriod-1);
double fps = 1000000.0/meanFrameTime;
saveFps(fps);
}
//render to the back buffer for this screen
renderToBackBuffer(i);
//display the back buffer
if(!TestDestroy())
m_renderData[i].deviceD3D9->Present(NULL, NULL, NULL, NULL);
//make sure we render to the correct back buffer next time
m_renderData[i].bufferToRender--;
//update the render cycle
m_renderData[i].renderStage=inVBlankRenderingComplete;
}
}
}
答案 0 :(得分:0)
不幸的是,在VS 2012和2013中,chrono::high_resolution_clock
未使用RDTSC。这是针对VS的未来版本修复的。见VS Connect。在此期间,请改用QPC。