Many object w/ vector?

[StoveBacon]

Ok so i know I've been asking a LOT of questions but i have some more because I've been messing around with game dev more and more.

So my first question is: how can I make multiple numbers of classes? like, i have a ball class and i want it to add a new ball at a random position when i press space.(and be able to iterate through and do collision) I've tried messing with it by using a vector but i can't quiet get it.

and also: were is the best place to put the buffer? Like is it best to have it just in main and pass it to every function that draw stuff?

thanks everyone for the help!

[Milch]

How to make multiple number of classes:
So you can choose: Should the number of objects be static or dynamic?
For static, you would do something like this:

Code: Select all

ClassName ObjectName;

The "tricky" part comes in if you want to make something dynamic.
Basically, you have 2 choices on how to do this.

1.
Make an dynamic array.
Basically, arrays are just pointers. So you can simply create an array with X numbers of elements doing this:

Code: Select all

ClassName* ObjectArray = new ClassName[NumberOfElements];
//Do stuff with it
delete[] ObjectArray; //Very important!

But a problem comes with this.
Array-Elements are created sequential, so you can imagine that as if they is just one big chunk in your memory, where all array-elements are stored in.
Because of this, you can "add to a pointer", e.g ObjectArray + 1 will give you the next element.
Now to the problem. Since arrays are build uppon this "one big chunk in memory", the PC cant guarantee that there is any free space near it - in case
you want to add elements. This would make the "ObjectArray + 1" unsafe, since it can just go out of bounds (e.g. the array continues 3 memory blocks further)
This makes the arrays kinda "unflexible", because you always have to make a new array,copy the old one to the new array and delete the old array.

2.
Linked Lists.
There are many ways to implement this, but I just explain the simplest one to you.
You can imagine linked-list like Objects floating around in memory and each object tells you where the next object is.
This way, you only have to know the first one, and then go from object to object till you reach the end.
Code wise, you have to change your class/structure a little bit.

Code: Select all

struct ABC 
{ 
  int I; //Some sort of data
  ABC* Next; //A pointer to the next element
}

Now, to go through all the elements, you do something like this:

Code: Select all

ABC* Actual = Start; //Start is the first element you created
while(Actual != NULL) //There needs to be somekind of end condition. So the last element in the list just pointes to NULL as next element
{
  cout << Actual->I << endl; //Print some data
  Actual = Actual->Next;
}

But this also creates a new problem.
Imagine this:
On a 32bit PC a pointer to an object takes up 4 bytes of memory.
A integer does also take up 4 bytes.
If you now have 1000 integers saves in a linked list, they will take up twice as much space.

So now you have to choose.
If you simply want to make a game with the max. 3 bullets - go with static arrays
If you want to make a list of something known (e.g. if you load a map you already know the number of tiles) go with dynamic arrays.
If you have something like enemies that spawn all over the place, get killed, spawn again,... you'll want to make a list.

Just in case you dont want to implement your own list - you can use the stl implementation: http://www.cplusplus.com/reference/stl/list/
Although, it might be a bit "overpowered" for your use, you can still consider it for starting/learing.

Hope that clears things up.

[adikid89]

You can do something like this:

Code: Select all

if(KeyPressed(sf::Key::Space)) {
   Ball* ball = new Ball;
   balls.push_back(ball);   //where balls is a vector<Ball*> which holds your balls :lol: 
}
//then you can iterate through your balls  :lol:  and update them
for(unsigned i = 0; i<balls.size() /* LOL */; i++) {
   balls[i]->Update();
}

[StoveBacon]

And I would also like to know what is the best way to represent a grid...
Would i be able to check the elements around it and below it if it was a vector?

[adikid89]

Wel...yeah...if you place them in order.
Example:
[ 00, 01, 02,
03, H, 04,
05, 06, 07 ]
Let's say the element the hero is standing on is i=4.The elements lower than the elements the hero is standing on are v.at((i+1)*titlesOnRow+j-1) - that is -one column to the left and one row down.. where i = i/titlesOnRow=4/3=1, j = i%titlesOnRow-1=4%3=1(to convert the 1d vector coords to a 2d vector coords)

[StoveBacon]

how would you do something like checking for collision like in tetris were the blocks under it stop it from moving?
i got one way to work but it sucked.
i had the for loop but then i had another for loop that checked them against each other but it didn't work.

[PaperDuckyFTW]

THen you would have a colision function inside the falling blocks class. Then, you would make a vector array (for example) of the blocks and for loop through the collision function.

Code: Select all

vector<TetrisBlocks*> Blocks;

for( int i = 0; i < Blocks.size(); i++ )
{
     if( !Blocks[i] ) continue;
     Blocks[i]->CheckCollision();
}

Or you could have it used inside the function, somethig like this:

Code: Select all

void TetrisBlocks::Update()
{
     if( CheckCollision() )
     {
          ypos -= yvel;
     }
}

Either way should work, but I'd suggest the second suggestion. Sorry if you already know this or it has already been said ^_^"

[StoveBacon]

but how would you check for collision?
the original way i did it was something like it iterates through it, and then it iterates through another one and it checks if the y of the first is equal to the y over the other one minus the height of the blocks.... this worked fine but when there were like 100 or so of them it started to get really slow.