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Draw circles using the polar coordinates and mid-point circle drawing algorithm on the same console using openGL in C++
  • Last Updated : 19 Apr, 2021

In this article, the task is to draw circles in two different subwindows using two different algorithms, and the circles are created using a single mouse click.

Approach:

  • There are two subwindows and both of them use different algorithms to create circles.
  • The left subwindow creates a circle using Midpoint Circle drawing algorithm and the right subwindow implements the concept of polar coordinates.
  • A circle can be created anywhere on the console using a single left mouse click and the coordinates of the center of the circle created depends on the position of the click.
  • To change the color of the circle, right-click on the mouse.
  • After performing all operations, jump out of the program by simply pressing the Esc key on the keyboard.

Below is the implementation of the above approach:

C++




// C++ program to implement onClick
// functionality in OpenGL to draw
// a circle using polar coordinates
// and midpoint algorithm
#include <GL/glut.h>
#include <iostream>
#include <math.h>
#include <stdlib.h>
#define xpix 500
#include <cstring>
using namespace std;
  
float r, g, b, x, y;
bool flag = true;
int counter = 0;
  
// Function to plot the coordinates
void plot(int x1, int y1)
{
    // Initialize the points
    glBegin(GL_POINTS);
  
    // Draw the vertex
    glVertex2i(x1 + x, y1 + y);
  
    // End
    glEnd();
}
  
// Function works on mouse click
void mouse(int button, int state,
           int mousex, int mousey)
{
    // Check if the current click
    // is left-click or not
    if (button == GLUT_LEFT_BUTTON
        && state == GLUT_DOWN) {
        flag = true;
        x = mousex;
        y = 600 - mousey;
    }
  
    // Check if the current click
    // is right-click or not
    else if (button == GLUT_RIGHT_BUTTON
             && state == GLUT_DOWN) {
        if (counter > 4) {
            counter = 0;
        }
  
        counter++;
  
        // Redisplay
        glutPostRedisplay();
    }
}
  
// Function that exits from program
void keyboard(unsigned char key,
              int x, int y)
{
    switch (key) {
    case 27:
        glutHideWindow();
    }
}
  
// Function to draw the circles using
// the midpoint circle algorithms
void midPointCircleDraw(void)
{
    // Change the color of circles on
    // the right click
    if (counter == 1) {
        glColor3f(1, 0, 0);
    }
    else if (counter == 2) {
        glColor3f(0, 1, 0);
    }
    else if (counter == 3) {
        glColor3f(0, 1, 1);
    }
    else if (counter == 4) {
        glColor3f(0.5, 0, 1);
    }
    else if (counter == 5) {
  
        glColor3f(0, 0.5, 1);
    }
  
    // Matrix mode
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
  
    // Given the coordinates
    gluOrtho2D(0.0, 400.0, 0.0, 600.0);
    int r = 50;
  
    if (flag) {
  
        // Begin the pointer
        glBegin(GL_POLYGON);
        int x1 = 0;
        int y1 = r;
  
        // Initialising the value
        // of the decision
        float decision = 5 / 4 - r;
  
        // Print the initial point on
        // the axes after translation
        plot(x1, y1);
  
        while (y1 > x1) {
  
            // Mid-point is inside or
            // on the perimeter
            if (decision < 0) {
                x1++;
                decision += 2 * x1 + 1;
            }
  
            // Mid-point is outside
            // the perimeter
            else {
                y1--;
                x1++;
                decision += 2 * (x1 - y1) + 1;
            }
  
            // Plot the points in the
            // different octants
            plot(x1, y1);
            plot(x1, -y1);
            plot(-x1, y1);
            plot(-x1, -y1);
            plot(y1, x1);
            plot(-y1, x1);
            plot(y1, -x1);
            plot(-y1, -x1);
        }
    }
  
    glFlush();
}
  
// Function to draw the circle using
// the polar coordinates
void polarCoordinateCircleDraw(void)
{
    float angle_theta;
  
    // Change the color of the circles
    // on right click
    if (counter == 1) {
        glColor3f(1, 0, 0);
    }
    else if (counter == 2) {
        glColor3f(0, 1, 0);
    }
    else if (counter == 3) {
        glColor3f(0, 1, 1);
    }
    else if (counter == 4) {
        glColor3f(0.5, 0, 1);
    }
    else if (counter == 5) {
  
        glColor3f(0, 0.5, 1);
    }
  
    // Matrix mode
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
  
    // Given the coordinates
    gluOrtho2D(0.0, 800.0, 0.0, 600.0);
    if (flag) {
  
        // Begin the pointer
        glBegin(GL_POLYGON);
  
        // Iterate through all the
        // 360 degres
        for (int i = 0; i < 360; i++) {
  
            angle_theta = i * 3.142 / 180;
            glVertex2f(x + 50 * cos(angle_theta),
                       y + 50 * sin(angle_theta));
        }
  
        // Set the vertex
        glEnd();
    }
  
    // Flushes the frame buffer to
    // the screen
    glFlush();
}
  
// Driver Code
int main(int argc, char** argv)
{
    // Initialize the drivers
    glutInit(&argc, argv);
  
    // Initialize the display mode
    glutInitDisplayMode(
        GLUT_SINGLE | GLUT_RGB);
  
    // Update the window size
    glutInitWindowSize(800, 600);
  
    // Update the window position
    glutInitWindowPosition(100, 100);
  
    int mainWindow = glutCreateWindow(
        "Circle Generation using "
        "Midpoint Algorithm on "
        "left and using Polar "
        "Coordinates on right");
  
    // Set the background color of
    // the right sub-window
    glClearColor(0, 0, 0, 0);
  
    // Clears the frame buffer
    glClear(GL_COLOR_BUFFER_BIT);
  
    // Links display event with the
    // display the event handler
    // (polarCoordinateCircleDraw)
    glutDisplayFunc(
        polarCoordinateCircleDraw);
  
    // Mouse event handler
    glutMouseFunc(mouse);
  
    // Create the sub-window to implement
    // midpoint algorithm on left
    int subWindow1
        = glutCreateSubWindow(
            mainWindow, 0, 0, 400, 600);
  
    glutInitWindowPosition(100, 100);
  
    // Sets the background color of
    // the left sub-window
    glClearColor(1, 0.5, 0.5, 1);
  
    // Clears the frame buffer
    glClear(GL_COLOR_BUFFER_BIT);
  
    // Links display event with the
    // display the event handler
    // (midPointCircleDraw)
    glutDisplayFunc(midPointCircleDraw);
  
    // Mouse event handler
    glutMouseFunc(mouse);
  
    // Keyboard event handler
    glutKeyboardFunc(keyboard);
  
    // Loops the current event
    glutMainLoop();
}

Output:

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