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Help with multiple shapes/sprites (SFML)

3 posts in this topic

Hi, ive been able to draw as many shapes as i desire using a vector, the problem is im unsure of how to interact with them individually.


say for example, i want the max amount of enemies allowed to spawn to be 5, and when one of the currently spawned enemies exits the screen, it 'dies' then another one is allowed to spawn.


or in the case if when im making a snake game, how would i go about only drawing 1 shape at the end of my snake each time the snake 'eats' the 'food'.


do i have to use iterators? what would i have to use to do this kind of thing?


im not asking for anyone to write the code for me, i just dont know what i need to be using, and i dont have much experience with std::vectors and pretty much none of iterators. so just reading the C++ doc really hasn't helped me figure this out.


this is the basic (probably not optimal) code i have for drawing multiple shapes with a vector.(not full source, just the code for the shape vector)

(what i see that i could do, but am not sure if optimal, or even if it will work as i havent tried yet, is have:


int MaxSpawn = 5;


if(Alive == true)


    for(int i = 0; i <= MaxSpawn; i++) Window.draw(Bricks[i]);


but thats not how i want to do it, because it doesnt do what i want still.

outside the main game loop:
sf::RectangleShape Square;

	vector<sf::RectangleShape> Bricks(10, sf::RectangleShape(Square));

	for (int i = 0; i < Bricks.size(); i++)
		Bricks[i].setSize(sf::Vector2f(25, 25));
		Bricks[i].setPosition(20 + (i * 15), Height/2);
inside main loop:
//Draw Here

		for(int i = 0; i < Bricks.size(); i++)



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Hi, ive been able to draw as many shapes as i desire using a vector, the problem is im unsure of how to interact with them individually.



To answer this directly. You have a couple of options. You can interact with each RectangleShape within the vector by doing what you are doing in the bricks loop:

vector<sf::RectangleShape> bricks(10, sf::RectangleShape(Square));


Alternatively you can host a vector of pointers to RectangleShapes

vector<sf::RectangleShape*> bricks;

RectangleShape some_shape = sf::RectangleShape();


some_shape.setPosition(40, 40); // now bricks[0].position == (40, 40)

To address your code example explicitly, I don't think storing a bunch of drawables in a "bricks" array in this case, or many cases, is necessary. For instance, it may be better to maintain some sort of Player object or Enemy object that stores an sf::IntRect or something similar. With that IntRect you can use the intersects() method to more easily detect collision, or in the case you mention, you can detect when  enemy.collision_rect.intersects(screen_bounds), or conversely, when it does not. This way you can have a vector filled with enemies, or entities and loop through and update their screen positions.

// Say an Enemy object has the members
class Enemy
    void update(); // updates position and updates bounds based on that
    sf::IntRect bounds;
    sf::Vector2f position;

// Elsewhere you can maintain some list of enemies

std::vector<Enemy> enemies;

// add enemies



// Iterate through them and update their position and bounds

for(std::vector<Enemy>::iterator itr=enemies.begin(); itr!=enemies.end(); itr++)
    itr->update(); // move each enemy 
    if(!itr->bounds.intersects(screen_bounds)) // check if off screen
        itr = enemies.erase(itr);              // if so, delete

// Then you can check the size of enemies and add new ones if needed

if(enemies.size != 5)
    // add new enemies

// Finally draw rects by translating one rectangle to the enemies positions
sf::RectangleShape draw_me;
for(auto& e : enemies)

I'm not sure I hit all the points in your post, but I tried to hit a few here! Let me know if any of this helps.


Within the code example I purposely used two other ways of iterating through a vector(since you already showed your knowledge of stepping through based on the vector.size()). 


WOW! Thanks a bunch!

I'm gonna mess around with this for a bit now


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Going on the notion of a snake game and now the snake is constantly expanding, try this idea:


Snake has edible items, and there seems to be a max when I play (like your max you noted). Store those edible items in whatever data structure you want (array, vector, list, etc) and make sure you have a way to keep track of whether they should be drawn, for instance when you are waiting a given amount of time to draw a new one.


For each snake (player and enemy), keep a list of coordinates to draw each chunk at. A std::vector of the SFML Vector2f (I think it's just in the sf namespace so sf::Vector2f) will suffice. Each item in your std::vector will be a point (x, y) that you need to draw a chunk of your snake. Create 2 (one for player, one for enemy) sprites that represent your snake chunks, like a green square and a red square, then iterate through each snake's vector, moving the sprite's position and then drawing it at that position:


for(int i = 0; i < player.positions.size() - 1; i++)
for(int i = 0; i < enemy.positions.size() - 1; i++)

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