Simple bouncing ball - OpenGL

sample program for bouncing ball - visualization

Code:

#include "stdafx.h"

#include <iostream>
#include <stdlib.h>

#include <GL/glut.h>

#include "math.h"

using namespace std;

int MAX_X=1200;
int MAX_Y=900;
const int MIN_X=0;
const int MIN_Y=0;
int m_x=0;
int m_y=0;

int ball_x=500;
int ball_y=500;
int radius = 30;
int poly_circle[20][2];
int circle_segments = 0;


// BY default ball will go up
int x_dir = 1;
int y_dir = -1;
int base_y;
int base_x;
float move_mag = 5.0;

void init_circle() {
    int x1=0;
    int y1=0;
    int cnt=0;
    float angle = 0;
    float x2,y2;
    for (angle = 0; angle < 360; angle+=25.0,cnt++) {
        float rad_angle = angle * 3.14 / 180;
        x2 = x1+radius * sin((double)rad_angle);
        y2 = y1+radius * cos((double)rad_angle);
        poly_circle[cnt][0] = x2;
        poly_circle[cnt][1] = y2;
    }
    poly_circle[cnt][0]=poly_circle[0][0];
    poly_circle[cnt][1]=poly_circle[0][1];
    circle_segments = cnt;
}



void drawScene();

void move_ball() {
    ball_x = ball_x + (move_mag*x_dir);
    ball_y = ball_y + (move_mag*y_dir);
}

void change_y_dir() {
    y_dir = -y_dir;
}
void change_x_dir() {
    x_dir = -x_dir;
}
void change_both_dir() {
    change_y_dir();
    change_x_dir();
}

int crossed_x_limits() {
    if((ball_x-radius)<=MIN_X) {
        return 1;
    }
    if((ball_x+radius)>=MAX_X) {
        return 1;
    }
    return 0;
}


int crossed_y_limits() {
    if(ball_y-radius<=MIN_Y) {
        return 1;
    }
    if(ball_y+radius>=MAX_Y) {
        return 1;
    }
    return 0;
}


// the mouse callback function:
void mouse_move(int x, int y)
{
    m_x = x;
    m_y = y;

   drawScene();
}


void handleResize(int w, int h) {
   
    glViewport(0, 0, w, h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    MAX_X = w;
    MAX_Y = h;
    gluOrtho2D(0, w, h, 0);
    glMatrixMode(GL_MODELVIEW);
}


void drawCircle(float radius, float x1, float y1)
{
    float angle = 0;
    float x2,y2,cx,cy,fx,fy;
    int cache = 0;

    glPushMatrix();//(NEW) Create a new matrix
    glTranslatef(x1,y1,0);//(NEW) Rotate the triangle on z axis based on how much time has passed

    glBegin(GL_LINES);
    for(int i=0; i<circle_segments;++i) {
        glVertex2f(poly_circle[i][0],poly_circle[i][1]);
        glVertex2f(poly_circle[i+1][0],poly_circle[i+1][1]);
    }
    glEnd();

    glPopMatrix();//(NEW) stops current transformations to the matrix
}

void play_ball() {
     move_ball();

    if (crossed_x_limits()) {
        change_x_dir();
    } else if (crossed_y_limits()) {
        change_y_dir();
    } else {
        // Do nothing
    }
}

void drawScene() {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
   
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
   
        glLineWidth(4);
    // Draw the ball
    play_ball();
    drawCircle(radius,ball_x,ball_y);

    glutSwapBuffers();
}

//Called every 25 milliseconds
void update(int value) {

    drawScene();

    glutPostRedisplay();
    glutTimerFunc(25, update, 0);
}

void idle_func(void) {
    drawScene();
}

void initRendering() {
    glEnable(GL_DEPTH_TEST);
   
}

void handleKeypress(unsigned char key, int x, int y) {
    switch (key) {
        case 27: //Escape key
            exit(0);

    }
}

void specialKey(int key, int x, int y) {
    switch (key) {
        case 101: //UP arrow key
            if (move_mag<radius-1) {
              move_mag+=0.5;
            }
            break;
        case 103: //DOWN arrow key
            if (move_mag>1) {
                move_mag-=0.5;
            }
            break;
    }
}


int main(int argc, char** argv) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
    glutInitWindowSize(MAX_X, MAX_Y);

    glutCreateWindow("Bouncing Ball");
    initRendering();
    init_circle();

    glutDisplayFunc(drawScene);
    glutSpecialFunc(specialKey);
    glutReshapeFunc(handleResize);
    glutMotionFunc(mouse_move);
    glutPassiveMotionFunc(mouse_move);
    glutTimerFunc(25 , update, 0);
    //glutIdleFunc(idle_func);

    glutMainLoop();
    return 0;
}

source : http://girish-errishuman.blogspot.com/20...-ball.html

nice and simple