Line Drawing Algorithms in Computer Graphics

Now, there are various ways for drawing lines in OpenGL, I will be using the classical algorithms - Digital Differential Analyzer (DDA) and Bresenham Line Drawing Algorithms.

Digital Differential Analyzer (DDA) Line Drawing Algorithm

#include <iostream>
using namespace std;
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <cmath>

void dda(float x1, float x2, float y1, float y2){
        float delX = x2 - x1;
        float delY = y2 - y1;
        float maxDiff = fmax(fabs(delX), fabs(delY));
        float minSteps = maxDiff / 0.00125f;
        float dx = delX / minSteps;
        float dy = delY / minSteps;
        glColor3f(0.078f, 0.75f, 0.078f);
        glPointSize(5.0f);
        glBegin(GL_POINTS);
        for (int i=0; i<ceil(minSteps); i++){
            float x= x1 + i*dx;
            float y= y1 + i*dy;
            glVertex2f(x, y);
        }
        glEnd();
}

int main()
{
    GLFWwindow* window;
    if (!glfwInit()){
        return -1;
    }
    window = glfwCreateWindow(640, 480, "DDA", NULL, NULL);
    if (!window)
    {
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);
    while (!glfwWindowShouldClose(window))
    {
        glClear(GL_COLOR_BUFFER_BIT);
        dda(-1.0f, 1.0f, -1.0f, 1.0f);    
        glfwSwapBuffers(window);
        glfwPollEvents();
    }
    glfwTerminate();
    return 0;
}

Bresenham Line Drawing Algorithm

#include <iostream>
using namespace std;
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <cmath>

void bresenham(float x1, float x2, float y1, float y2){
        float delX = x2 - x1;
        float delY = y2 - y1;

        float pixelX = x1 < x2 ? 0.01f : -0.01f;
        float pixelY = y1 < y2 ? 0.01f : -0.01f; 

        float pixel = delX - delY;
        glColor3f(0.078f, 0.75f, 0.078f);
        glPointSize(5.0f);
        glBegin(GL_POINTS);
        while(true){
            glVertex2f(x1, y1);

            if(x1>=x2 && y1>=y2){
                break;
            }

            float nextPixel = 2 * pixel;

            if(nextPixel > -delY){
                pixel -= delY;
                x1 += pixelX;
            }

            if(nextPixel < delX){
                pixel += delX;
                y1 += pixelY;
            }
        }
        glEnd();
}

int main()
{
    GLFWwindow* window;
    if (!glfwInit()){
        return -1;
    }
    window = glfwCreateWindow(640, 480, "Bresenham Line Drawing Algorithm", NULL, NULL);
    if (!window)
    {
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);
    while (!glfwWindowShouldClose(window))
    {
        glClear(GL_COLOR_BUFFER_BIT);
        bresenham(-0.5f, 0.5f, -0.5f, 0.5f);  
        glfwSwapBuffers(window);
        glfwPollEvents();
    }
    glfwTerminate();
    return 0;
}