How to prevent objects from intersecting in C++? - c++

Question

I have been working on creating a pong game in C++ and am facing issues with how my ball and paddle collide. Virtually, when the ball hits the paddle from the top, the ball bounces off. But if the ball hits the paddle from the side, the ball slides along the paddle like its caught and only bounces back off once it reaches the other end. I've tried messing around with the dimensions of the collision box for the paddle and using the clock method to try and count how long the ball has been colliding with the paddle, and neither have worked. Can anyone help out with this?
My main code:
#include "RealBat.h"
#include <sstream>
#include <string>
#include <cstdlib>
#include <SFML/Graphics.hpp>
#include <iostream>
using namespace sf;
int windowWidth = 1024;
int windowHeight = 868;
Bat bat(windowWidth / 2, windowHeight - 50);
sf::Vector2f ballUpdate(sf::Vector2f ballPosition, int windowWidth, int windowHeight, float *velocityX, float *velocityY){
sf::Vector2f ballPosition2 = sf::Vector2f(ballPosition.x, ballPosition.y);
ballPosition2.x += *velocityX;
ballPosition2.y += *velocityY;
if (ballPosition2.x >= windowWidth || ballPosition2.x <= 0) {
*velocityX *= -1.0f;
}
if (ballPosition2.y >= windowHeight || ballPosition2.y <= 0) {
*velocityY *= -1.0f;
}
int ballBottomLeft = ballPosition2.y + 9;
int ballRight = ballPosition2.x + 9;
int batRight = bat.getVector().x + 100;
int score = 0;
if (ballBottomLeft >= bat.getVector().y) {
if (ballPosition2.x >= bat.getVector().x && ballRight <= batRight) {
std::cout << "collisionTracker" << std::endl;
*velocityY *= -1.0f;
score = score + 1;
}
else {
score = 0;
}
return ballPosition2;
}
int main()
{
float velocityX = 0.05;
float velocityY = 0.05;
sf::Vector2f position = sf::Vector2f(10, 10);
RectangleShape ball = RectangleShape();
ball.setSize(sf::Vector2f (10, 10));
RenderWindow window(VideoMode(windowWidth, windowHeight), "ID PONG");
while (window.isOpen()) {
Event event;
while (window.pollEvent(event)) {
if (event.type == Event::Closed) {
window.close();
}
}
if (Keyboard::isKeyPressed(Keyboard::Left)) {
bat.moveLeft();
}
else if (Keyboard::isKeyPressed(Keyboard::Right)) {
bat.moveRight();
}
bat.update();
position = ballUpdate(position, windowWidth, windowHeight, &velocityX, &velocityY);
ball.setPosition(position);
window.clear(Color(148, 213, 0, 255));
window.draw(bat.getShape());
window.draw(ball);
window.display();
}
}
My Bat Header File:
#pragma once
#include <SFML/Graphics.hpp>
using namespace sf;
class Bat {
private:
Vector2f position;
RectangleShape batShape;
float batSpeed = .3f;
public:
Bat(float startX, float startY);
FloatRect getPosition();
RectangleShape getShape();
Vector2f getVector();
void moveLeft();
void moveRight();
void update();
};
My Bat cpp:
#include "RealBat.h"
Bat::Bat(float startX, float startY)
{
position.x = startX;
position.y = startY;
batShape.setSize(sf::Vector2f(100, 10));
batShape.setPosition(position);
}
FloatRect Bat::getPosition()
{
return batShape.getGlobalBounds();
}
RectangleShape Bat::getShape()
{
return batShape;
}
void Bat::moveLeft()
{
position.x -= batSpeed;
}
void Bat::moveRight()
{
position.x += batSpeed;
}
void Bat::update()
{
batShape.setPosition(position);
}
sf::Vector2f Bat::getVector () {
return position;
}

Answer 1

Most likely what is happening is that the ball is still within the boundary of the bat on the next time round the loop.
Picture the ball and bat like this terrible ascii representation (+ for bat, 0 for ball), ball has just hit bats right side, heading down and to the left
+--------------+
+ +
+ O
+ +
+--------------+
balls y velocity will be reversed and next iteration it will be
+--------------+
+ O+
+ +
+ +
+--------------+
This is still inside the ball's boundary, so its y velocity will be reversed again giving
+--------------+
+ +
+ O +
+ +
+--------------+
So the ball will bounce up and down inside the bat until it hits the left hand edge.
+--------------+
+ O O O O O O O+
+O O O O O O O O
+ +
+--------------+
One way to fix this would be to only reverse the Y velocity if the ball is heading down, that way the ball would just continue upwards even though it is still inside the bat. Possibly by adding:
if (*velocityY > 0.0) {
just above the collisionTracker cout call, so you don't score or bounce when heading upwards.

Answer 2

I had something of a similar issue when I made my pong game years ago. This is because we only check intersection and change the direction of velocity in x-axis. So when it hit from the sides the velocity is constantly inverting every frame. The way I solved it at the time was by checking the position of the center of my ball with respect to the bounds (sides) of the paddle. So, when the ball is hitting any of the sides I simply invert the direction of velocity in the y-axis. This way the ball hits the paddle and just moves away.
I'm pretty sure there's better ways to do it but I was only a beginner at the time and this was the best I could come up with.