How to give a name to an image in a loop? - c++

Question

I just started programming with SFML, I'm trying to make something shoot a bullet. Currently I have made the bullet move one way when I press space. But I cannot shoot multiple bullets at the same time, it just uses the same image. I can't figure out what I should do, if I should give each bullet it's own name?
Also should I delete it when it's out from the window? If I should how can I do it?
Here's the relevant code:
void Game::handleWeaponInput(sf::Keyboard::Key key, bool isPressed)
{
if (key == sf::Keyboard::Space)
{
mIsFired = isPressed;
if (!mBulletTexture.loadFromFile("Media/Textures/Bullet.png"))
{
}
mBullet.setTexture(mBulletTexture);
mBullet.setPosition(100.f, 100.f);
mBullet.setRotation(90.f);
}
}
And:
void Game::update(sf::Time elapsedTime)
{
sf::Vector2f bulletMovement(0.f, 0.f);
if (mIsFired)
bulletMovement.x += 300.f;
mBullet.move(bulletMovement * elapsedTime.asSeconds());
}

Answer 1

One thing you can do is create a std::vector of bullets so you can track each one individually.
class Game
{
sf::Texture mBulletTexture;
// declare a std::vector of bullets
std::vector<sf::Sprite> mBullets;
public:
void handleWeaponInput(sf::Keyboard::Key key, bool isPressed);
void update(sf::Time elapsedTime);
};
void Game::handleWeaponInput(sf::Keyboard::Key key, bool isPressed)
{
if (key == sf::Keyboard::Space)
{
mIsFired = isPressed;
if (!mBulletTexture.loadFromFile("Media/Textures/Bullet.png"))
{
}
mBullets.emplace_back(); // add another sf::Sprite to vector
mBullets.back().setTexture(mBulletTexture);
mBullets.back().setPosition(100.f, 100.f);
mBullets.back().setRotation(90.f);
}
}
void Game::update(sf::Time elapsedTime)
{
sf::Vector2f bulletMovement(0.f, 0.f);
if (mIsFired)
bulletMovement.x += 300.f;
// move each bullet in the vector
for(auto& bullet: mBullets)
bullet.move(bulletMovement * elapsedTime.asSeconds());
}
Obviously this exact code won't work properly as you will also have to manage how each bullet moves (what direction etc....). But hopefully it will give you an idea how you could scale from one bullet to many bullets.
It may be worth defining a class Bullet that contains the sf::Sprite along with information about the bullet's speed and direction?
Then you could make your vector with those:
class Bullet
{
sf::Sprite sprite;
sf::Texture texture;
sf::Vector2f direction;
public:
// ...
};
class Game
{
// declare a std::vector of bullets
std::vector<Bullet> mBullets;
// ...
};

Answer 2

first of all, I want to tackle your update method: You should update each existing bullet each frame independently of whether you fired one or not:
void Game::update(sf::Time elapsedTime) {
sf::Vector2f bulletMovement(300.f, 0.f);
for (auto& bullet : mBullets) // range-based-for and auto require C++11
bullet.move(bulletMovement * elapsedTime.asSeconds());
}
As others have already suggested, for a simple use case, a vector of bullets works nicely. If you need more complex data structures to handle your game entities, try researching on things like "scene graph" or "quad tree".
std::vector<sf::Sprite> mBullets;
to add a bullet, simply use
// possibly construct sprite seperatly and add some transforms beforehand
mBullets.push_back(sf::Sprite(/* however you store your texture */));
And yes, it is a good idea to destroy bullets once they are outside of your screen, since you would be wasting draw calls and other operations on entities which you will never see again. Using the tools SFML already provides, one could do it like this:
void Game::destroyBulletsOutsideView() {
sf::FloatRect viewBounds(0, 0, mWindow.getSize().x, mWindow.getSize().y);
for (auto iter = mBullets.begin(); iter != mBullets.end(); ++iter) {
if (!viewBounds.intersects(iter->getGlobalBounds())
mBullets.erase(iter);
}
}
Side note: You will likely want to add something like a reload or cooldown time to your Bullets, so you can't shoot tons of bullets per second.