InitOpenGL_2.cpp

//-----------------------------------------------------------------------------
// InitOpenGL_2.cpp by Steve Jones 
// Copyright (c) 2015-2016 Game Institute. All Rights Reserved.
//
// Creates a basic resizeable window and OpenGL 3.3 context using GLFW.
// Creates onKey keyboard handler callback and sets the Escape key to exit
// the program.
// Creates FPS counter and displays in app title bar
//-----------------------------------------------------------------------------
#include <iostream>
#include <sstream>
#define GLEW_STATIC
#include "GL/glew.h"	// Important - this header must come before glfw3 header
#include "GLFW/glfw3.h"


// Global Variables
const char* APP_TITLE = "Introduction to Modern OpenGL - Hello Window 2";
const int gWindowWidth = 800;
const int gWindowHeight = 600;

// Function prototypes
void glfw_onKey(GLFWwindow* window, int key, int scancode, int action, int mode);  
void showFPS(GLFWwindow* window);

//-----------------------------------------------------------------------------
// Main Application Entry Point
//-----------------------------------------------------------------------------
int main()
{
	// Intialize GLFW 
	// GLFW is configured.  Must be called before calling any GLFW functions
	if (!glfwInit())
	{ 
		// An error occured
		std::cerr << "GLFW initialization failed" << std::endl;
		return -1;
	}

	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
	glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);	// forward compatible with newer versions of OpenGL as they become available but not backward compatible (it will not run on devices that do not support OpenGL 3.3

	// Create an OpenGL 3.3 core, forward compatible context window
	GLFWwindow* pWindow = glfwCreateWindow(gWindowWidth, gWindowHeight, APP_TITLE, NULL, NULL);
	if (pWindow == NULL)
	{
		std::cerr << "Failed to create GLFW window" << std::endl;
		glfwTerminate();
		return -1;
	}

	// Make the window's context the current one
	glfwMakeContextCurrent(pWindow);

	// Initialize GLEW
	glewExperimental = GL_TRUE;
	if (glewInit() != GLEW_OK)
	{
		std::cerr << "Failed to initialize GLEW" << std::endl;
		return -1;
	}

	// Set the required callback functions
	glfwSetKeyCallback(pWindow, glfw_onKey);

	// Rendering loop
	while (!glfwWindowShouldClose(pWindow))
	{
		showFPS(pWindow);

		// Poll for and process events
		glfwPollEvents();

		// Render the scene
		glClearColor(0.23f, 0.38f, 0.47f, 1.0f); 
		glClear(GL_COLOR_BUFFER_BIT);

		// Swap front and back buffers
		glfwSwapBuffers(pWindow);
	}

	// Clean up
	glfwTerminate();

	return 0;
}

//-----------------------------------------------------------------------------
// Is called whenever a key is pressed/released via GLFW
//-----------------------------------------------------------------------------
void glfw_onKey(GLFWwindow* window, int key, int scancode, int action, int mode)
{
	if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
		glfwSetWindowShouldClose(window, GL_TRUE);
}

//-----------------------------------------------------------------------------
// Code computes the average frames per second, and also the average time it takes
// to render one frame.  These stats are appended to the window caption bar.
//-----------------------------------------------------------------------------
void showFPS(GLFWwindow* window)
{
	static double previousSeconds = 0.0;
	static int frameCount = 0;
	double elapsedSeconds;
	double currentSeconds = glfwGetTime(); // returns number of seconds since GLFW started, as double float
	
	elapsedSeconds = currentSeconds - previousSeconds;

	// Limit text updates to 4 times per second
	if (elapsedSeconds > 0.25)
	{
		previousSeconds = currentSeconds;
		double fps = (double)frameCount / elapsedSeconds;
		double msPerFrame = 1000.0 / fps;

		// The C++ way of setting the window title
		std::ostringstream outs;
		outs.precision(3);	// decimal places
		outs << std::fixed 
			 << APP_TITLE << "    "
			 << "FPS: " << fps << "    "
			 << "Frame Time: " << msPerFrame << " (ms)";
		glfwSetWindowTitle(window, outs.str().c_str());

		// Reset for next average.
		frameCount = 0;
	}

	frameCount++;
}