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fix(render): Preserve frame limiter deadlines so a 60 fps cap runs at 60 #647

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fix(render): Preserve frame limiter deadlines so a 60 fps cap runs at 60 #647

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2 changes: 2 additions & 0 deletions Core/GameEngine/Include/Common/FrameRateLimit.h
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,8 @@ class FrameRateLimit
private:
Int64 m_freq;
Int64 m_start;
Int64 m_lastActual;
UnsignedInt m_previousFps;
};


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21 changes: 19 additions & 2 deletions Core/GameEngine/Source/Common/FrameRateLimit.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -28,13 +28,20 @@ FrameRateLimit::FrameRateLimit()
QueryPerformanceCounter(&start);
m_freq = freq.QuadPart;
m_start = start.QuadPart;
m_lastActual = m_start;
m_previousFps = 0;
}

Real FrameRateLimit::wait(UnsignedInt maxFps)
{
PROFILER_SECTION;
LARGE_INTEGER tick;
QueryPerformanceCounter(&tick);
if (m_previousFps != maxFps)
{
m_start = m_lastActual;
}
m_previousFps = maxFps;
double elapsedSeconds = static_cast<double>(tick.QuadPart - m_start) / m_freq;
const double targetSeconds = 1.0 / maxFps;
const double sleepSeconds = targetSeconds - elapsedSeconds - 0.002; // leave ~2ms for spin wait
Expand All @@ -54,15 +61,25 @@ Real FrameRateLimit::wait(UnsignedInt maxFps)
}
while (elapsedSeconds < targetSeconds);

m_start = tick.QuadPart;
return (Real)elapsedSeconds;
const Int64 period = static_cast<Int64>(static_cast<double>(m_freq) / maxFps + 0.5);
const Int64 deadline = m_start + period;
const double actualSeconds = static_cast<double>(tick.QuadPart - m_lastActual) / m_freq;
m_lastActual = tick.QuadPart;
// Preserve small overshoot, but discard long pauses instead of banking catch-up.
if (tick.QuadPart - deadline < period)
m_start = deadline;
else
m_start = tick.QuadPart;
return static_cast<Real>(actualSeconds);
}

void FrameRateLimit::reset()
{
LARGE_INTEGER tick;
QueryPerformanceCounter(&tick);
m_start = tick.QuadPart;
m_lastActual = m_start;
m_previousFps = 0;
}


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