About CollisionManagerGrid

[che...@sina.com]

when calculating cell_width in __init__() function of CollisionManagerGrid, it says: 

1. in objects with same size case:

    cell_width = 1.25 * object width

2. in mixed width case:

    cell_width = 1.25 * {width (object): all objects not exceptionally big}

    what does it mean??? 

    what is the value of cell_width on earth in such case?

[claudio canepa]

Suppose you have  100 collidables with dimensions between 16 and 32, and then four big collidables  400 x 400

A good cell_width would be 1.25 * 32

A grid collision maneager works by

  - breaks the world in cells

  - each object is added to all the cells its overlap

  - when asking for collision with object A, we need to look only in the cells overlapped by A

So, if the cell size is too big they are too many objects to look in each cell.

On the other side, if cell size is too small, object A will overlap too many cells.

 If all the collidables are same size,and small relative to world size, cell_width as 1.25 * cell_width works well.

What if all the collidables are small relative to world size but not same size?. Well, 1.25 * max_width may be good enough.

What if a few big objects are added to the previous scenary ? Discard the big objects to calculate cell_width

What if theres no small size bigger than most of collidables sizes? Then probably the grid manager will not behave well, a quadtree would be better suited

   

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[che...@sina.com]

Thanks Claudio so much for your clear explanation. 

so based on my understanding,  I  guess  the statement like this would be better:

cell_width = 1.25 * max {width (object): all objects not exceptionally big} 

[claudio canepa]

Yes, i will change the docstring, thanks.

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