Hi! =)
I´m programming a little game where a ball flies through the window and when it hits the end of the window it shall change its direction. Here´s the code I´m using for this:
void Ball::update(float frametime)
{
if (pSpriteB->getPosition().y >= 9)
{
pSpriteB->move(-400 * frametime, -400 * frametime);
}
else if (pSpriteB->getPosition().y <= 9)
{
pSpriteB->move(400 * frametime, 400 * frametime);
}
}
But when the ball hits the window´s end, it just stops and vibrates a bit. What I thought was that the previous movement is still active and I have to end up this previous movement so that the new movement direction can be done without errors, but I didn´t find anything to end up a movement.
What shall I do? Why isn´t it moving correctly? Please help! :D
Ok, as promised, here's a simple example of a bouncing ball.
Stick it in a file called bounce.cc and then you can build it (on Linux) like this:
$ clang++ -std=c++11 -lsfml-window -lsfml-graphics -lsfml-system -o bounce bounce.cc
and then run it like so: $ ./bounce
Each time you run the program the ball will get a random direction and speed, so run it a few times to see different bounces.
#include <SFML/Graphics.hpp>
#include <random>
#include <functional>
#include <cstdlib>
#include <cmath>
int main()
{
const int window_width = 400;
const int window_height = 300;
const float ball_radius = 16.f;
const int bpp = 32;
sf::RenderWindow window(sf::VideoMode(window_width, window_height, bpp), "Bouncing ball");
window.setVerticalSyncEnabled(true);
std::random_device seed_device;
std::default_random_engine engine(seed_device());
std::uniform_int_distribution<int> distribution(-16, 16);
auto random = std::bind(distribution, std::ref(engine));
sf::Vector2f direction(random(), random());
const float velocity = std::sqrt(direction.x * direction.x + direction.y * direction.y);
sf::CircleShape ball(ball_radius - 4);
ball.setOutlineThickness(4);
ball.setOutlineColor(sf::Color::Black);
ball.setFillColor(sf::Color::Yellow);
ball.setOrigin(ball_radius / 2, ball_radius / 2);
ball.setPosition(window_width / 2, window_height / 2);
sf::Clock clock;
sf::Time elapsed = clock.restart();
const sf::Time update_ms = sf::seconds(1.f / 30.f);
while (window.isOpen()) {
sf::Event event;
while (window.pollEvent(event)) {
if ((event.type == sf::Event::Closed) ||
((event.type == sf::Event::KeyPressed) && (event.key.code == sf::Keyboard::Escape))) {
window.close();
break;
}
}
elapsed += clock.restart();
while (elapsed >= update_ms) {
const auto pos = ball.getPosition();
const auto delta = update_ms.asSeconds() * velocity;
sf::Vector2f new_pos(pos.x + direction.x * delta, pos.y + direction.y * delta);
if (new_pos.x - ball_radius < 0) { // left window edge
direction.x *= -1;
new_pos.x = 0 + ball_radius;
} else if (new_pos.x + ball_radius >= window_width) { // right window edge
direction.x *= -1;
new_pos.x = window_width - ball_radius;
} else if (new_pos.y - ball_radius < 0) { // top of window
direction.y *= -1;
new_pos.y = 0 + ball_radius;
} else if (new_pos.y + ball_radius >= window_height) { // bottom of window
direction.y *= -1;
new_pos.y = window_height - ball_radius;
}
ball.setPosition(new_pos);
elapsed -= update_ms;
}
window.clear(sf::Color(30, 30, 120));
window.draw(ball);
window.display();
}
return EXIT_SUCCESS;
}