BasicTimer.h

#pragma once

#include <wrl.h>

// Helper class for basic timing.
ref class BasicTimer sealed
{
public:
	// Initializes internal timer values.
	BasicTimer()
	{
		if (!QueryPerformanceFrequency(&m_frequency))
		{
			throw ref new Platform::FailureException();
		}
		Reset();
	}
	
	// Reset the timer to initial values.
	void Reset()
	{
		Update();
		m_startTime = m_currentTime;
		m_total = 0.0f;
		m_delta = 1.0f / 60.0f;
	}
	
	// Update the timer's internal values.
	void Update()
	{
		if (!QueryPerformanceCounter(&m_currentTime))
		{
			throw ref new Platform::FailureException();
		}
		
		m_total = static_cast<float>(
			static_cast<double>(m_currentTime.QuadPart - m_startTime.QuadPart) /
			static_cast<double>(m_frequency.QuadPart)
			);
		
		if (m_lastTime.QuadPart == m_startTime.QuadPart)
		{
			// If the timer was just reset, report a time delta equivalent to 60Hz frame time.
			m_delta = 1.0f / 60.0f;
		}
		else
		{
			m_delta = static_cast<float>(
				static_cast<double>(m_currentTime.QuadPart - m_lastTime.QuadPart) /
				static_cast<double>(m_frequency.QuadPart)
				);
		}
		
		m_lastTime = m_currentTime;
	}
	
	// Duration in seconds between the last call to Reset() and the last call to Update().
	property float Total
	{
		float get() { return m_total; }
	}
	
	// Duration in seconds between the previous two calls to Update().
	property float Delta
	{
		float get() { return m_delta; }
	}

private:
	LARGE_INTEGER m_frequency;
	LARGE_INTEGER m_currentTime;
	LARGE_INTEGER m_startTime;
	LARGE_INTEGER m_lastTime;
	float m_total;
	float m_delta;
};