SFML Movement with mouse event - sfml

Question

I'm new to SFML currently I'm trying to make a simple 2D golf ball physics. Right now, I have a class called Ball that contain the attributes of the ball sprite, position, velocity etc. I would call the call class it in main and it working as expected, but the one thing that didn't work is it would just move/teleport the ball to the next position rather than moving the ball like expected.
void Ball::move(sf::Vector2f& velocity)
{
// boundaries
if (ballSprite.getPosition().x < 0 - 49 || ballSprite.getPosition().x > 700 - 70)
{
velocity.x *= (float) -1;
}
if (ballSprite.getPosition().y < 0 - 30 || ballSprite.getPosition().y > 1200 - 70)
{
velocity.y *= (float) -1;
}
if (ballSprite.getPosition().x + 1 == 700 || ballSprite.getPosition().x - 1 == 0)
{
velocity.x *= -1;
}
if (ballSprite.getPosition().y + 1 == 1200 || ballSprite.getPosition().y - 1 == 0)
{
velocity.y *= -1;
}
ballSprite.move(velocity.x, velocity.y);
sf::Texture ballTex;
ballTex.loadFromFile("ball2.png");
Ball gameBall(1, ballTex);
while (window.isOpen())
{
sf::Event event;
bool mouseReleased = false;
while (window.pollEvent(event))
{
if (event.type == sf::Event::Closed)
{
window.close();
}
if (event.type == sf::Event::MouseButtonPressed)
{
cout << "Mouse Button Pressed\n";
}
mouseReleased = false;
if (event.mouseButton.button == sf::Mouse::Left && event.type == sf::Event::MouseButtonReleased)
{
mouseReleased = true;
cout << "Mouse Button Released\n";
cout << "Ball Position: " << gameBall.getSprite().getPosition().x << "," << gameBall.getSprite().getPosition().y << endl;
sf::Vector2i velo = sf::Mouse::getPosition(window);
cout << "Velocity: " << velo.x - gameBall.getSprite().getPosition().x << ", " << -1 * (velo.y - gameBall.getSprite().getPosition().y) << endl;
sf::Vector2f velocity(-1 *(velo.x - gameBall.getSprite().getPosition().x) , (-1 * (velo.y - gameBall.getSprite().getPosition().y)));
gameBall.move(velocity);
cout << "Ball Position After: " << gameBall.getSprite().getPosition().x << "," << gameBall.getSprite().getPosition().y << endl;
}
}
I'm not sure how to update the ball so it would show the ball move on the screen rather than teleporting to a new position on the screen.

Answer 1

The way you are calculating the change in position is simply a delta of position i.e. movining your ball by the delta will result in teleporting to the destination. The delta itself is really useful.
One way to make it work is to devide the delta into smaller parts (ball speed) and move by these parts.
However, it seems to me that it is easier to calculate the normalized vector (unit vector) and multiply by the ball speed, then fix it (if needed) by multiplying by sqrt of 2 (to prevent faster movement on diagonal).
This method is not very accurate, the ball would only move in 8 directions (it doesn't keep the vector ratio) so if you need it to be more realistic i.e. keep the ratio of x and y delta you can calculate it like that:
sf::Vector2f stretchVector(const sf::Vector2f& vector, const float& radius)
{
sf::Vector2i xySymb(1, 1);//calculation of the symbol(-/+)
xySymb.x = isPositive(vector.x);//isPositive should return -1 or (1 when>=0)
xySymb.y = isPositive(vector.y);
//dealing with [0,...] or [0,0] vectors and the 0 radius.
if (radius == 0.f)
return sf::Vector2f(0.f, 0.f);
if (vector.y == 0.f or vector.x == 0.f) {
if (vector.x == vector.y) {
return sf::Vector2f(0.f, 0.f);
}
if (vector.x != 0.f) {
return sf::Vector2f(radius*xySymb.x, 0.f);
}
return sf::Vector2f(0.f, radius*xySymb.y);
}
//<------------------------------------------------>
else {
float ratio = abs(vector.x / vector.y);
float x, y;
x = sqrt((radius * radius * ratio * ratio) / (1 + ratio * ratio));
y = sqrt(abs(radius * radius - x * x));
return sf::Vector2f(float(x * xySymb.x), float(y * xySymb.y));
}
}
I didn't know how to name the function but it can stretch and shrink to provided radius.
The example stretchVector call:
sf::Vector2f deltaPosition(mousePos.x-ballPos.x,mousePos.y-ballPos.y);
sf::Vector2f desiredMove = stretchVector(deltaPositon, ballSpeed);
ball.move(desiredMove);