How to draw SFML shapes stored in a vector - c++

Question

I'm making a copy of the game "Asteroids" using SFML.
To store all my asteroids I use a std::vector<sf::ConvexShape> vector, which stores all of the asteroid shapes. The problem is drawing the shapes from the vector. I looked at this post and saw that I could use an iterator to draw my shapes (I know he used sprites in that post but I presume it makes no difference if I were to use shapes.)
So I tried that:
for(std::vector<sf::ConvexShape>::iterator it=allShapes.begin();it!= allShapes.end(); ++it){
window.draw(*it);
}
And that throws an exception, terminating my program.
FYI: above, allShapes contains sf::ConvexShape shapes.
So the question is: How do I draw shapes that I store in a vector?
Full sauce:
using namespace std;
class asteroid{
public:
sf::Vector2f pos;
double angle;
void update(sf::Vector2f);
void create(std::vector<sf::ConvexShape>);
};
/* Will be implemented later
void asteroid::update(sf::Vector2f a){
pos += a;
};
*/
void asteroid::create(std::vector<sf::ConvexShape> a){
cout << "Creating..." << endl;
a.push_back(sf::ConvexShape()); //New asteroid SHAPE
std::vector<sf::ConvexShape>::iterator tempIt = a.end();
tempIt->setPointCount(4);
for(int i = 0; i < tempIt->getPointCount()+1; i++){ //Drawing asteroid
tempIt->setPoint(i, sf::Vector2f(i*100, i*100));
}
tempIt->setFillColor(sf::Color::White);
cout << "Done!" << endl;
};
int main()
{
// Init //
sf::RenderWindow window(sf::VideoMode(200, 200), "SFML works!");
std::vector<sf::ConvexShape> allShapes; //List of all asteroid SHAPES
std::vector<asteroid> allAsteroids; //List of asteroid CLASS OBJECTS
allAsteroids.push_back(asteroid()); //New asteroid CLASS OBJECT
for(std::vector<asteroid>::iterator it = allAsteroids.begin(); it != allAsteroids.end(); ++it){ //Creating asteroids
it->create(allShapes);
}
// Loop //
while (window.isOpen())
{
// Event //
sf::Event event;
while (window.pollEvent(event))
{
if (event.type == sf::Event::Closed)
window.close();
}
// Display //
window.clear();
for(std::vector<sf::ConvexShape>::iterator it = allShapes.begin(); it != allShapes.end(); ++it){
window.draw(*it);
}
window.display();
}
return 0;
}

Answer 1

You have a few problems here...
First:
std::vector<sf::ConvexShape>::iterator tempIt = a.end();
tempIt->setPointCount(4);
end() does NOT give you an iterator to the last element in the vector - it gives you an iterator to the "element" just past it, and is used for bounds checking (e.g. in a for loop). In other words it does not point to valid data, so the second line is invalid. There are many approaches you could use here; the following two are "most correct" though:
//with iterators using a.end() - 1
std::vector<sf::ConvexShape>::iterator tempIt = a.end() - 1;
tempIt->setPointCount(4);
//with back, accessing the element directly
a.back().setPointCount(4);
Secondly:
for(int i = 0; i < tempIt->getPointCount()+1; i++)
The asteroid has four points, so getPointCount()+1 = 5. This means that the loop executes for i = 0, 1, 2, 3, and 4 - one too many times.
Thirdly:
tempIt->setPoint(i, sf::Vector2f(i*100, i*100));
This line runs once for each i. Assuming you make the change above, this results in the points (0,0), (100, 100), (200, 200), and (300, 300). This is a line, not a convex shape. You will need to revise your formula. Setting the points directly is also a fine option, as there are only 4 to set.
You also may want to pass the vector by reference to avoid making any unnecessary copies:
void create(std::vector<sf::ConvexShape>& a){
//...
}