FrameRateLimit addon for OpenSiv3D 0.6.x

FrameRateLimitAddon_for_OpenSiv3D.cpp

// License: CC0 1.0

# include <Siv3D.hpp>

class FrameRateLimit : public IAddon
{
private:
	static constexpr std::chrono::steady_clock::duration kMaxDrift = 10ms;

	int32 m_targetFPS;

	std::chrono::time_point<std::chrono::steady_clock> m_sleepUntil;

public:
	explicit FrameRateLimit(int32 targetFPS)
		: m_targetFPS(targetFPS)
		, m_sleepUntil(std::chrono::steady_clock::now() - kMaxDrift)
	{
	}

	virtual void postPresent() override
	{
		// Determine the end time of sleep until the next frame
		m_sleepUntil += std::chrono::duration_cast<std::chrono::steady_clock::duration>(1s) / m_targetFPS;

		// Set a lower limit so that m_sleepUntil does not go back in time from the current time if the target frame rate is not reached
		// (Because even if you sleep until the exact current time, there might be a long wait time depending on the environment, 
		//  so as a countermeasure, we are setting the time subtracted by kMaxDrift as the lower limit)
		const auto sleepUntilLowerLimit = std::chrono::steady_clock::now() - kMaxDrift;
		if (m_sleepUntil < sleepUntilLowerLimit)
		{
			m_sleepUntil = sleepUntilLowerLimit;
		}

		// Execute sleep
		std::this_thread::sleep_until(m_sleepUntil);
	}

	void setTargetFPS(int32 targetFPS)
	{
		m_targetFPS = targetFPS;
	}
};

void Main()
{
	// Set frame rate
	constexpr int32 kTargetFPS = 300;
	Addon::Register(U"FrameRateLimit", std::make_unique<FrameRateLimit>(kTargetFPS));

	// Disable VSync
	Graphics::SetVSyncEnabled(false);

	const Font font{ FontMethod::MSDF, 48, Typeface::Bold };
	while (System::Update())
	{
		// Show frame rate
		font(U"{}fps"_fmt(Profiler::FPS())).draw();
	}
}