chess board

#include <stdlib.h>
#include <stdio.h>
#include <string.h>

#include <GLFW/glfw3.h>
#include <gl/GL.h>


void render_loop()
{
    glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT);

    float x1 = 10.0f, y1 = 15.0f;
    float x2 = 80.0f, y2 = 95.f;
    int i, j;

    for (i = 1; i <= 8; i++) {
        for (j = 1; j <= 8; j++) {
            if ((j+i) % 2 == 0)
                glColor3f(0.0, 0.0, 0.0);
            else
                glColor3f(1.0, 1.0, 1.0);

            glBegin(GL_POLYGON);
                glVertex2f(x1, y1);
                glVertex2f(x2, y1);
                glVertex2f(x2, y2);
                glVertex2f(x1, y2);
            glEnd();

            x1 += 70.0f;
            x2 += 70.0f;
        }
        x1 = 10.0f;
        x2 = 80.0f;
        y1 += 80.0f;
        y2 += 80.0f;
    }
}

/* program entry */
int main(int argc, char *argv[])
{
    GLFWwindow* window;

    if (!glfwInit())
    {
        fprintf(stderr, "Failed to initialize GLFW\n");
        exit(EXIT_FAILURE);
    }

    glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);
    window = glfwCreateWindow(660, 610, "LearnOpenGL", NULL, NULL);
    if (!window)
    {
        fprintf(stderr, "Failed to open GLFW window\n");
        glfwTerminate();
        exit(EXIT_FAILURE);
    }


    glfwMakeContextCurrent(window);
    glfwSwapInterval(1);

    // set up view
    glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT);
    glViewport(0, 0, 800, 600);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    // see https://www.opengl.org/sdk/docs/man2/xhtml/glOrtho.xml
    glOrtho(0.0, 700.0, 0.0, 650.0, 0.0, 1.0); // this creates a canvas you can do 2D drawing on


    // Main loop
    while (!glfwWindowShouldClose(window))
    {
        // Draw gears
        render_loop();
        // Swap buffers
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    // Terminate GLFW
    glfwTerminate();

    // Exit program
    exit(EXIT_SUCCESS);
}