Re: [pygame] How to rotate a rect

[Paul Sidorsky <paulsid@home.com>]

Leonardo Santagada wrote:

> Making the box is not the problem but how to make fast collision detection?

This may not be suitable for your situation but I'll describe it anyhow
since I haven't seen it mentioned yet:

Give each object a radius or size and then use the distance formula.  If
the distance between two objects is less than the combined radiuses (or
half the combined sizes) of the objects, they collide.  To avoid
floating point, use the squared distance.  Here's pseudo code:

limitsize = (object1.size1 + object2.size2) / 2
limitsize *= limitsize
distsquared = (object2.x - object1.x) + (object2.y - object1.y)
if distsquared <= limitsize:
    # Boom!

This works great for spherical objects and can work for others if you
don't need 100% precision.  The inaccuracy increases as the sizes get
larger.  I'm not sure how practical this method is in "real" games since
I've only tried it on a small scale, but it might be worth a shot.

-- 
======================================================================
Paul Sidorsky                                          Calgary, Canada
paulsid@home.com                      http://members.home.net/paulsid/
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