Linux.h

// Simple GNU/Linux OpenGL framework for implementing:
// http://gafferongames.com/game-physics/fix-your-timestep/
//
// Instructions:
// 1) Add the following to Timestep.cpp:
// #include "Linux.h"
//
// 2) Compile with:
// g++ -O2 -g -D__LINUX__ Timestep.cpp -o timestep -lglut -lGL -lGLU -lrt

#ifdef __LINUX__

#ifndef LINUX_GUARD_H_
#define LINUX_GUARD_H_

#include <GL/freeglut.h>
#include <ctime>

void keyPressed(unsigned char key, int x, int y)
{
    if (key == 27)
        onQuit();
}

int window;

bool openDisplay(const char title[], int width, int height)
{
    // create window
    // keep glut happy
    static int argc = 1;
    glutInit(&argc, NULL);
    glutInitDisplayMode(GLUT_DOUBLE);
    glutInitWindowSize(width, height);
    window = glutCreateWindow(title);

    // set the kpress callback, must be done
    // AFTER the window has been created
    glutKeyboardFunc(keyPressed);

    return true;
}

void updateDisplay()
{
    // process pending events
    glutMainLoopEvent();

    // Flush the OpenGL buffers to the window
    glutSwapBuffers();
}

void closeDisplay()
{
    glutDestroyWindow(window);
    window = 0;
}

float time()
{
    static timespec start = {0, 0};

    if (start.tv_sec == 0 and start.tv_nsec == 0) {
        clock_gettime(CLOCK_MONOTONIC, &start);
        return 0.0f;
    }

    timespec counter = {0, 0};
    clock_gettime(CLOCK_MONOTONIC, &counter);
    return (counter.tv_sec - start.tv_sec) +
        ((counter.tv_nsec - start.tv_nsec) / 1e9f);
}

#endif   // LINUX_GUARD_H_
#endif   // __LINUX__