gistfile1.txt

#include <stdio.h>  // fprintf, sprintf, stderr
#include <stdlib.h> // exit
#include <math.h>   // sqrt

#include <GLFW/glfw3.h>
#include <Windows.h>

// global variables
// we'll use global variables, since the GLFW callback functions we will add
// later will require access to these variables. 
GLFWwindow* window;
double resx = 640, resy = 480;

// this function will be called internally by GLFW whenever an error occur.
void error_callback(int error, const char* description);

// we move all the initialization step into a function for brevity
// we'll put all future additional initialization of GLFW and similar functionality in here
int init();


int main()
{
	if (!init()) {
		printf("Could not init. Exiting\n");
		return -1;
	}
	// set the background color to red
	glClearColor(1.0, 0.0, 0.0, 1.0);

	// main loop
	while (!glfwWindowShouldClose(window)) {
		glfwPollEvents();

		glClear(GL_COLOR_BUFFER_BIT); // actually clear the window

		glfwSwapBuffers(window);
	}

	glfwTerminate();

	return 0;
}

int init()
{
	// initialize all the internal state of GLFW
	if (!glfwInit()) {
		fprintf(stderr, "Error initializing GLFW\n");
		return 0;
	}

	// tell GLFW to call error_callback if an internal error ever occur at some point inside GLFW functions.
	glfwSetErrorCallback(error_callback);

	// create the window
	window = glfwCreateWindow(resx, resy, "Checkpoint 2: Using OpenGL functions.", NULL, NULL);

	// check if the opening of the window failed whatever reason and clean up
	if (!window) {
		glfwTerminate();
		return 0;
	}

	// in principle we can have multiple windows, 
	// so we set the newly created on as "current"
	glfwMakeContextCurrent(window);

	// Enable v-sync for now, if possible
	glfwSwapInterval(1);
	return 1; // success
}

void error_callback(int error, const char* description)
{
	fprintf(stderr, "Error: %s (%d)\n", description, error);
}