Draw Some Basic Shapes Using OpenGL

Here, we are required to draw some basic shapes (squares, triangles, etc.) using OpenGL.

We use the so-called "old-fashioned" OpenGL.

Below is the code.

#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <iostream>
#include <GL/gl.h>
#include <GL/glut.h>

using namespace std;


void renderScene(void)
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    // Draw a green triangle.
    glBegin(GL_TRIANGLES);
    glColor3f(0.0f, 1.0f, 0.0f);
    glVertex3f(0.3, 0.3, 0.0);
    glVertex3f(0.4, 0.4, 0.0);
    glVertex3f(0.4, 0.6, 0.0);
    glEnd();

    // Different colors for each vertex.
    glBegin(GL_TRIANGLES);
    glColor3f(1.0f, 0.0f, 0.0f);
    glVertex3f(0.0, 0.1, 0.0);
    glColor3f(0.0f, 1.0f, 0.0f);
    glVertex3f(0.1, -0.1, 0.0);
    glColor3f(0.0f, 0.0f, 1.0f);
    glVertex3f(-0.1, -0.1, 0.0);
    glEnd();
    
    // Draw a line.
    glBegin(GL_LINE_STRIP);
    glColor3f(1.0f, 0.0f, 0.0f);
    glVertex2f(0.5, 0.5);
    glVertex2f(0.7, 0.7);
    glEnd();

    // Draw a polygon.
    glBegin(GL_POLYGON);
    glVertex2f(0.75, 0.75);
    glVertex2f(0.75, 0.95);
    glVertex2f(0.95, 0.95);
    glVertex2f(0.95, 0.75);
    glEnd();

    // Draw a triangle strip.
    glBegin(GL_TRIANGLE_STRIP);
    glVertex2f(-0.3, -0.3);
    glVertex2f(-0.3, -0.5);
    glVertex2f(-0.6, -0.7);
    glVertex2f(-0.6, -0.4);
    glVertex2f(-0.9, -0.9);
    glEnd();
    
    glFlush();
}

int main(int argc, char *argv[])
{
    glutInit(&argc, argv);
    glutCreateWindow("Hello OpenGL");
    glutDisplayFunc(renderScene);
    glutMainLoop();
    return 0;

}

This is by far the simplest implementation of drawing a triangle using OpenGL I have seen on the Internet. I'm sure you are going to appreciate this, because it's really simple.