#include <GL/glew.h>
#include <GL/freeglut.h>
#include <cstdio>

void display() {
    glClear(GL_COLOR_BUFFER_BIT);
    glBegin(GL_TRIANGLES);
    glColor3f(1.0, 0.0, 0.0);
    glVertex2f(-0.5, -0.5);
    glColor3f(0.0, 1.0, 0.0);
    glVertex2f(0.5, -0.5);
    glColor3f(0.0, 0.0, 1.0);
    glVertex2f(0.0, 0.5);
    glEnd();
    glFlush();
}

void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
    glViewport(0, 0, width, height);
} 

int main(int argc, char** argv) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
    glutInitWindowSize(800, 600);
    glutCreateWindow("OpenGL Example");
    GLenum err = glewInit();
    if (GLEW_OK != err) {
        fprintf(stderr, "GLEW error: %s\n", glewGetErrorString(err));
        return 1;
    }

    glViewport(0, 0, 800, 600);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
    glutDisplayFunc(display);
    glutMainLoop();
    return 0;
}