glfw/src/win32/win32_time.c

//========================================================================
// GLFW - An OpenGL framework
// Platform:    Win32/WGL
// API version: 3.0
// WWW:         http://www.glfw.org/
//------------------------------------------------------------------------
// Copyright (c) 2002-2006 Marcus Geelnard
// Copyright (c) 2006-2010 Camilla Berglund <elmindreda@elmindreda.org>
//
// This software is provided 'as-is', without any express or implied
// warranty. In no event will the authors be held liable for any damages
// arising from the use of this software.
//
// Permission is granted to anyone to use this software for any purpose,
// including commercial applications, and to alter it and redistribute it
// freely, subject to the following restrictions:
//
// 1. The origin of this software must not be misrepresented; you must not
//    claim that you wrote the original software. If you use this software
//    in a product, an acknowledgment in the product documentation would
//    be appreciated but is not required.
//
// 2. Altered source versions must be plainly marked as such, and must not
//    be misrepresented as being the original software.
//
// 3. This notice may not be removed or altered from any source
//    distribution.
//
//========================================================================

#include "internal.h"


//////////////////////////////////////////////////////////////////////////
//////                       GLFW internal API                      //////
//////////////////////////////////////////////////////////////////////////

//========================================================================
// Initialise timer
//========================================================================

void _glfwInitTimer(void)
{
    __int64 freq;

    // Check if we have a performance counter
    if (QueryPerformanceFrequency((LARGE_INTEGER*) &freq))
    {
        // Performance counter is available => use it!
        _glfwLibrary.Win32.timer.HasPerformanceCounter = GL_TRUE;

        // Counter resolution is 1 / counter frequency
        _glfwLibrary.Win32.timer.Resolution = 1.0 / (double) freq;

        // Set start time for timer
        QueryPerformanceCounter((LARGE_INTEGER*) &_glfwLibrary.Win32.timer.t0_64);
    }
    else
    {
        // No performace counter available => use the tick counter
        _glfwLibrary.Win32.timer.HasPerformanceCounter = GL_FALSE;

        // Counter resolution is 1 ms
        _glfwLibrary.Win32.timer.Resolution = 0.001;

        // Set start time for timer
        _glfwLibrary.Win32.timer.t0_32 = _glfw_timeGetTime();
    }
}


//////////////////////////////////////////////////////////////////////////
//////                       GLFW platform API                      //////
//////////////////////////////////////////////////////////////////////////

//========================================================================
// Return timer value in seconds
//========================================================================

double _glfwPlatformGetTime(void)
{
    double t;
    __int64 t_64;

    if (_glfwLibrary.Win32.timer.HasPerformanceCounter)
    {
        QueryPerformanceCounter((LARGE_INTEGER*) &t_64);
        t =  (double)(t_64 - _glfwLibrary.Win32.timer.t0_64);
    }
    else
        t = (double)(_glfw_timeGetTime() - _glfwLibrary.Win32.timer.t0_32);

    // Calculate the current time in seconds
    return t * _glfwLibrary.Win32.timer.Resolution;
}


//========================================================================
// Set timer value in seconds
//========================================================================

void _glfwPlatformSetTime(double t)
{
    __int64 t_64;

    if (_glfwLibrary.Win32.timer.HasPerformanceCounter)
    {
        QueryPerformanceCounter((LARGE_INTEGER*) &t_64);
        _glfwLibrary.Win32.timer.t0_64 = t_64 - (__int64) (t / _glfwLibrary.Win32.timer.Resolution);
    }
    else
        _glfwLibrary.Win32.timer.t0_32 = _glfw_timeGetTime() - (int)(t * 1000.0);
}