[英]Limiting fps with std::chrono
std::chrono::system_clock::time_point m_BeginFrame = std::chrono::system_clock::now();
std::chrono::system_clock::time_point m_EndFrame = std::chrono::system_clock::now();
std::chrono::nanoseconds m_WorkTime = std::chrono::nanoseconds::zero();
std::chrono::nanoseconds m_WaitTime = std::chrono::nanoseconds::zero();
auto invFpsLimit = std::chrono::nanoseconds(1e9 / fpsLimit());
// main loop
while (!glfwWindowShouldClose(m_pScreen->glfwWindow()))
{
m_WaitTime = m_BeginFrame - m_EndFrame;
m_EndFrame = std::chrono::system_clock::now();
m_WorkTime = m_EndFrame - m_BeginFrame;
// if need sleep
if (m_WorkTime < invFpsLimit)
{
std::this_thread::sleep_until(m_BeginFrame + invFpsLimit);
m_DeltaTime = invFpsLimit;
}
else
{
m_DeltaTime = m_WorkTime;
}
m_BeginFrame = std::chrono::system_clock::now();
TRACE(" %f %u %u %u",
((float)1e9 / (float)(m_WaitTime.count() + m_WorkTime.count())),
m_WorkTime.count(),
m_WaitTime.count(),
invFpsLimit.count());
// think and opengl stuff...
}
I'm trying to limit fps with this code, but Fraps showes me about 56-57 value我正在尝试使用此代码限制 fps,但 Fraps 向我显示了大约 56-57 的值
58.848454 3175500 13817300 16666666
55.259304 3314200 14782300 16666666
58.923698 2321700 14649400 16666666
56.200928 2167400 15625900 16666666
52.774071 3188200 15760500 16666666
50.600887 4899700 14862800 16666666
65.011055 2347500 13034500 16666666
54.966499 2611700 15581200 16666666
55.605911 2653400 15330300 16666666
56.476437 2386100 15320400 16666666
55.280689 2581400 15508100 16666666
56.437550 2355400 15363300 16666666
47.170700 5535900 15663700 16666666
64.713608 3039700 12413000 16666666
56.136570 2941100 14872600 16666666
53.444496 3624200 15086800 16666666
60.074493 2397500 14248500 16666666
51.737339 3777100 15551300 16666666
59.369026 3665800 13178000 16666666
59.355282 3543900 13303800 16666666
54.243759 3961000 14474300 16666666
45.764706 7823500 14027400 16666666
61.242237 6239400 10089200 16666666
73.396652 2013800 11610800 16666666
50.531849 3824000 15965500 16666666
62.895454 2796000 13103400 16666666
60.611572 2360500 14138000 16666666
56.074242 2241700 15591800 16666666
55.143208 2454800 15679800 16666666
I have tried to change clock to system_clock, use sleep_for instead of sleep_untill, nothing works我试图将时钟更改为 system_clock,使用 sleep_for 而不是 sleep_untill,没有任何效果
Is there some specific thing I don't khow about std clocks or working code I can't see?有什么我不知道的关于标准时钟或我看不到的工作代码的具体事情吗?
What is stealing my fps?什么偷了我的fps?
One can do better by updating m_BeginFrame
and m_EndFrame
by invFpsLimit
instead of by system_clock::now()
.通过使用
invFpsLimit
而不是system_clock::now()
更新m_BeginFrame
和m_EndFrame
可以做得更好。 This might look something like:这可能类似于:
#include <iostream>
#include <thread>
int fpsLimit() {return 60;}
int
main()
{
using namespace std::chrono;
using dsec = duration<double>;
auto invFpsLimit = duration_cast<system_clock::duration>(dsec{1./fpsLimit()});
auto m_BeginFrame = system_clock::now();
auto m_EndFrame = m_BeginFrame + invFpsLimit;
unsigned frame_count_per_second = 0;
auto prev_time_in_seconds = time_point_cast<seconds>(m_BeginFrame);
while (true)
{
// Do drawing work ...
// This part is just measuring if we're keeping the frame rate.
// It is not necessary to keep the frame rate.
auto time_in_seconds = time_point_cast<seconds>(system_clock::now());
++frame_count_per_second;
if (time_in_seconds > prev_time_in_seconds)
{
std::cerr << frame_count_per_second << " frames per second\n";
frame_count_per_second = 0;
prev_time_in_seconds = time_in_seconds;
}
// This part keeps the frame rate.
std::this_thread::sleep_until(m_EndFrame);
m_BeginFrame = m_EndFrame;
m_EndFrame = m_BeginFrame + invFpsLimit;
}
}
In C++17 and forward, I recommend constructing invFpsLimit
with round
instead of duration_cast
for slightly better accuracy:在 C++17 及以后的版本中,我建议使用
round
而不是duration_cast
构造invFpsLimit
以获得稍微更好的准确性:
auto invFpsLimit = round<system_clock::duration>(dsec{1./fpsLimit()});
要获得增量,您可以执行以下操作:
unsgined deltaTime = 1000.0f / frame_count_per_fps; // In milliseconds
The documentation of sleep_until
says: sleep_until
的文档说:
The function also may block for longer than until after sleep_time has been reached due to scheduling or resource contention delays.
由于调度或资源争用延迟,该函数也可能会阻塞更长的时间,直到到达 sleep_time 之后。
If you really need exact fps use either vSync, or replace the if block in your code with the following loop which continually does nothing until the frame time is used up:如果您确实需要精确的 fps,请使用 vSync,或使用以下循环替换代码中的 if 块,该循环在帧时间用完之前会持续执行任何操作:
while (m_WorkTime < invFpsLimit)
{
m_EndFrame = std::chrono::system_clock::now();
m_WorkTime = m_EndFrame - m_BeginFrame;
}
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