Question

Working on game where plates will be falling from top to bottom. Some plates will also “bounce” on the ground and then start moving upwards again. This leads situations where a falling plate collides with a “rising plate”.

My problem? I don´t know how to detect this collision.

Since all the plates comes from the same class I can´t write
if(CGRectIntersectsRect([self boundingBox], [self boudingBox]))
since this statement will always be true.

I create the plates with a for-loop:

for(i=0; i<9; i++){

 Plate *plate = [Plate initPlate];

}

and then just reuse these plates throughout the game.

Any ideas or work arounds on how I detect a collision between two plates? Any advice would be greatly appreciated.

Regards.

Answer 1

You need to have a class that manages (for example using a NSMutableArray) the set of plates, and instead of checking for collisions on the Plate class you do it on this new class.

Assuming your array is:

NSMuttableArray *plateSet

You can do this:

for (Plate *bouncingPlate in plateSet)
{
    if ([bouncingPlate bouncing])
    {
        for (Plate *fallingPlate in plateSet)
        {
            if (![fallingPlate bouncing])
            {
                /* Check for collision here between fallingPlate and bouncingPlate */
            }
        }
    }
}

Or, more elegantly:

for (Plate *bouncingPlate in plateSet)
{
    if (![bouncingPlate bouncing])
    {
        continue;
    }

    for (Plate *fallingPlate in plateSet)
    {
        if ([fallingPlate bouncing])
        {
            continue;
        }
        /* Check for collision here between fallingPlate and bouncingPlate */
    }
}