[Beginner] Help with Bouncing Circles

[Cadisol87]

You forgot to move ball so it doesn't collide anymore. For example ball at {x:50 y:0} and radius 10 should be moved to {x: 50 y:10}.

Okay, but what can I do to solve this Problem? First I set every x and y Speed to over 50, but that didnt work. So I think I misunderstood you 

Which Values do I need to change?

[krzat]

I meant position. If RightBorderTouching returns true, you should move the ball and then change velocity.

[Cadisol87]

Wow, thanks krzat!   

I modified my code and now it looks like this:

for(int i = 0; i < 10; i++  )
    {
        if(RightBorderTouching(Ball[i].getPosition().x)) {Ball[i].move( -ballradius * dt, 0 * dt); xSpeed[i] = -xSpeed[i];}
        if(LeftBorderTouching(Ball[i].getPosition().x)) {Ball[i].move(  ballradius * dt, 0 * dt); xSpeed[i] = -xSpeed[i];}
        if(TopBorderTouching(Ball[i].getPosition().y)) {Ball[i].move(  0 * dt, ballradius * dt); ySpeed[i] = -ySpeed[i];}
        if(BottomBorderTouching(Ball[i].getPosition().y)){Ball[i].move( 0 * dt, -ballradius * dt); ySpeed[i] = -ySpeed[i];}
    }

I think the Problem is gone now!

(If I did something wrong please tell me  )

[Cadisol87]

Ok, today I finally got time to continue working on my project.

I created a bool to check for collisions:

bool Collision(const float& TempPositionY1, const float& TempPositionY2, const float& TempPositionX1, const float& TempPositionX2)
    {
        int distance = ((TempPositionX1 - TempPositionX2) * (TempPositionX1 - TempPositionX2)) + ((TempPositionY1 - TempPositionY2) * (TempPositionY1 - TempPositionY2));
        if (distance < ballradius + ballradius )
        {
            return true;
        }
        else return false;

    }

Okay, I think this should work.
But now I have to create a loop to check all possible combinations of Collisions.

I created something like that first:

for (int i = 0; i < ballcount; i++)  
{  
    for (int j = i + 1; j < ballcount; j++)  
    {  
        if (Collision(Ball[i].getPosition().y, Ball[j].getPosition().y, Ball[i].getPosition().x, Ball[j].getPosition().x))
        {
            // Calculate new direction
        }
    }
}

But that doesnt detect all the collisions, for example Ball[4] and Ball[8].

So my question is:

How can I effectively cover all the possible Collisions in my loop?

[Nexus]

You forgot to square the radiuses.

Short tip: You should abstract your code to make it much more readable.
How I would write the collision:

float SquaredLength(sf::Vector2f vector);
float Square(float value);

// 1. vectors instead of floats
// 2. pass by value instead of reference (for floats for sure, for vectors it's arguable)
// 3. shorter names (lhs, rhs are conventions for "left/right hand side")
bool Collision(sf::Vector2f lhs, sf::Vector2f rhs)
{
    // 4. reuse existing functions
    // 5. instead of      if (...) return true; else return false;
    //         write      return ...;
    return SquaredLength(lhs - rhs) < Square(2*ballRadius);
}

If you deal a lot with vector operations, you could reuse the functions I wrote inThor.Vectors. You don't need to build Thor for that, the Vectors module is header-only and can be used directly.

[Cadisol87]

Thanks, Nexus!

But when I try to compile my code, it gives me these two errors: undefined reference to `SquaredLength(sf::Vector2<float>)', and
 undefined reference to `Square(float)'.

Heres my if-statement:

    sf::Vector2f lhs(Ball[1].getPosition().y, Ball[1].getPosition().x);
    sf::Vector2f rhs(Ball[2].getPosition().y, Ball[2].getPosition().x);
    if (Collision(lhs,  rhs))
        {

        }

What did I do wrong?

[eXpl0it3r]

You need to implement SquaredLength and Square of course. Nexus just gave the deceleration of the function.

[Jesper Juhl]

You did not implement the functions.

[Cadisol87]

Im not getting it...
I declared Squared Length and Square at the Beginning:

    float SquaredLength(sf::Vector2f vector);
    float Square(float value);

Heres my Collision Bool:

  bool Collision(sf::Vector2f lhs, sf::Vector2f rhs)
{
    return SquaredLength(lhs - rhs) < Square(2*ballradius);
}
 

And heres my if-statement:

    sf::Vector2f lhs(Ball[1].getPosition().y, Ball[1].getPosition().x);
    sf::Vector2f rhs(Ball[2].getPosition().y, Ball[2].getPosition().x);
    if (Collision(lhs,  rhs))
        {
        }

Okay, and what has to be implemented now?
For me, this seems very plausible.

Oh god, im feeling stupid right now...

[Jesper Juhl]

You have declared the signatures of the functions but you have not implemented them.
They are not pre-existing functions. You have to write their actual implementation yourself.

[Cadisol87]

Ahh, thanks Jesper, now I understand... 



For me! 

[Cadisol87]

Okay, I've got a function for calculating the Square:

float Square(float value)
{
    return value * value;
}
 

It think this should work.

But what is the Squared lenght?
Which lenght do you mean?
How do I have to calculate that?

[wintertime]

The squared length is what you get from the dot product of a vector with itself. Its an optimization to not take the squareroot of it when you just need it for comparing it with another length and just square that length instead.

[Nexus]

As stated earlier:

If you deal a lot with vector operations, you could reuse the functions I wrote in Thor.Vectors. You don't need to build Thor for that, the Vectors module is header-only and can be used directly.

You can also have a look at the documentation and/or implementation in order to understand what these functions do. But they require some basic knowledge about vector algebra.

[Cadisol87]

Okay, but where can I find the Header for SFML 2.1?