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++ 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 degrees
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:
