How to add several bouncing balls using multithreading in opengl c++ - c++

Question

I'm very new to OpenGL. I have a simple program that allows me to have once bouncing ball. Do you know how I can tweek the code to have two or more balls bounce (using multithreads)? I'm also supposed to have the balls bounce off each other should a collision occur. Here is the code I have for one bouncing ball.
/*
* GL07BouncingBall.cpp: A ball bouncing inside the window
*/
#include <string>
#include <iostream>
#include <thread>
using namespace std;
#include <windows.h> // for MS Windows
#include <GL/glut.h> // GLUT, includes glu.h and gl.h
#include <Math.h> // Needed for sin, cos
#define PI 3.14159265f
// Global variables
char title[] = "Bouncing Ball (2D)"; // Windowed mode's title
int windowWidth = 640; // Windowed mode's width
int windowHeight = 480; // Windowed mode's height
int windowPosX = 50; // Windowed mode's top-left corner x
int windowPosY = 50; // Windowed mode's top-left corner y
GLfloat ballRadius = 0.2f; // Radius of the bouncing ball
GLfloat ballX = 0.0f; // Ball's center (x, y) position
GLfloat ballY = 0.0f;
GLfloat ballXMax, ballXMin, ballYMax, ballYMin; // Ball's center (x, y) bounds
GLfloat xSpeed = 0.02f; // Ball's speed in x and y directions
GLfloat ySpeed = 0.007f;
int refreshMillis = 30; // Refresh period in milliseconds
// Projection clipping area
GLdouble clipAreaXLeft, clipAreaXRight, clipAreaYBottom, clipAreaYTop;
/* Initialize OpenGL Graphics */
void initGL() {
glClearColor(0.0, 0.0, 0.0, 1.0); // Set background (clear) color to black
}
/* Callback handler for window re-paint event */
void display() {
glClear(GL_COLOR_BUFFER_BIT); // Clear the color buffer
glMatrixMode(GL_MODELVIEW); // To operate on the model-view matrix
glLoadIdentity(); // Reset model-view matrix
glTranslatef(ballX, ballY, 0.0f); // Translate to (xPos, yPos)
// Use triangular segments to form a circle
glBegin(GL_TRIANGLE_FAN);
glColor3f(0.0f, 0.0f, 1.0f); // Blue
glVertex2f(0.0f, 0.0f); // Center of circle
int numSegments = 100;
GLfloat angle;
for (int i = 0; i <= numSegments; i++) { // Last vertex same as first vertex
angle = i * 2.0f * PI / numSegments; // 360 deg for all segments
glVertex2f(cos(angle) * ballRadius, sin(angle) * ballRadius);
}
glEnd();
glutSwapBuffers(); // Swap front and back buffers (of double buffered mode)
// Animation Control - compute the location for the next refresh
ballX += xSpeed;
ballY += ySpeed;
// Check if the ball exceeds the edges
if (ballX > ballXMax) {
ballX = ballXMax;
xSpeed = -xSpeed;
} else if (ballX < ballXMin) {
ballX = ballXMin;
xSpeed = -xSpeed;
}
if (ballY > ballYMax) {
ballY = ballYMax;
ySpeed = -ySpeed;
} else if (ballY < ballYMin) {
ballY = ballYMin;
ySpeed = -ySpeed;
}
}
/* Call back when the windows is re-sized */
void reshape(GLsizei width, GLsizei height) {
// Compute aspect ratio of the new window
if (height == 0) height = 1; // To prevent divide by 0
GLfloat aspect = (GLfloat)width / (GLfloat)height;
// Set the viewport to cover the new window
glViewport(0, 0, width, height);
// Set the aspect ratio of the clipping area to match the viewport
glMatrixMode(GL_PROJECTION); // To operate on the Projection matrix
glLoadIdentity(); // Reset the projection matrix
if (width >= height) {
clipAreaXLeft = -1.0 * aspect;
clipAreaXRight = 1.0 * aspect;
clipAreaYBottom = -1.0;
clipAreaYTop = 1.0;
} else {
clipAreaXLeft = -1.0;
clipAreaXRight = 1.0;
clipAreaYBottom = -1.0 / aspect;
clipAreaYTop = 1.0 / aspect;
}
gluOrtho2D(clipAreaXLeft, clipAreaXRight, clipAreaYBottom, clipAreaYTop);
ballXMin = clipAreaXLeft + ballRadius;
ballXMax = clipAreaXRight - ballRadius;
ballYMin = clipAreaYBottom + ballRadius;
ballYMax = clipAreaYTop - ballRadius;
}
/* Called back when the timer expired */
void Timer(int value) {
glutPostRedisplay(); // Post a paint request to activate display()
glutTimerFunc(refreshMillis, Timer, 0); // subsequent timer call at milliseconds
}
/* Main function: GLUT runs as a console application starting at main() */
int main(int argc, char** argv) {
glutInit(&argc, argv); // Initialize GLUT
glutInitDisplayMode(GLUT_DOUBLE); // Enable double buffered mode
glutInitWindowSize(windowWidth, windowHeight); // Initial window width and height
glutInitWindowPosition(windowPosX, windowPosY); // Initial window top-left corner (x, y)
glutCreateWindow(title); // Create window with given title
glutDisplayFunc(display); // Register callback handler for window re-paint
glutReshapeFunc(reshape); // Register callback handler for window re-shape
glutTimerFunc(0, Timer, 0); // First timer call immediately
initGL(); // Our own OpenGL initialization
glutMainLoop(); // Enter event-processing loop
return 0;
}
**Edit:
I've added improvements to my code. I've now created two balls, each with its own speed, color, and center. Although, the two balls remain static. The function in which I create the balls is defined by:
void create(double s, GLfloat ballRadius, GLfloat ballX, GLfloat ballY, GLfloat xSpeed, GLfloat ySpeed)//, double r, double t)
{
//ballRadius = f;
//xSpeed = r;
//ySpeed = t;
glTranslatef(ballX, ballY, 0.0f); // Translate to (xPos, yPos)
glBegin(GL_TRIANGLE_FAN);
glColor3f(s, 0.0f, 1.0f); // Blue
glVertex2f(0.0, 0.0f); // Center of circle
int numSegments = 100;
GLfloat angle;
for (int i = 0; i <= numSegments; i++) { // Last vertex same as first vertex
angle = i * 2.0f * PI / numSegments; // 360 deg for all segments
glVertex2f(cos(angle) * ballRadius, sin(angle) * ballRadius);
}
glEnd();
// Animation Control - compute the location for the next refresh
ballX += xSpeed;
ballY += ySpeed;
// Check if the ball exceeds the edges
if (ballX > ballXMax) {
ballX = ballXMax;
xSpeed = -xSpeed;
} else if (ballX < ballXMin) {
ballX = ballXMin;
xSpeed = -xSpeed;
}
if (ballY > ballYMax) {
ballY = ballYMax;
ySpeed = -ySpeed;
} else if (ballY < ballYMin) {
ballY = ballYMin;
ySpeed = -ySpeed;
}
}
And I call this function by:
create(1.0, 0.2f, 0.0f, 0.0f, 0.02f, 0.007f);
create(0.0, 0.1f, 0.0f, 0.0f, 0.04f, 0.014f);
for two separate balls

Answer 1

This code "creates" a circle
// Use triangular segments to form a circle
glBegin(GL_TRIANGLE_FAN);
glColor3f(0.0f, 0.0f, 1.0f); // Blue
glVertex2f(0.0f, 0.0f); // Center of circle
int numSegments = 100;
GLfloat angle;
for (int i = 0; i <= numSegments; i++) { // Last vertex same as first vertex
angle = i * 2.0f * PI / numSegments; // 360 deg for all segments
glVertex2f(cos(angle) * ballRadius, sin(angle) * ballRadius);
}
glEnd();