# physics - a simple framework for very lightweight physics simulations

'''

A simple framework for very lightweight physics simulations.

ABSTRACT

    This library creates a basis for simulating physical interactions
    between simple bodies.  Suitable for little pygame usage, or demos.
    For much more full-featured physics, check out the PyODE bindings.

AUTHOR

    Ed Halley (ed@halley.cc) 17 October 2007

'''

import math
import vectors ; from vectors import *
import interpolations ; from interpolations import *

#----------------------------------------------------------------------------

class Body (object):
    '''The base class of all simple physical entities.'''

    def __init__(self):
        '''There are no members in the abstract root body.'''
        pass

    def collides(self, other): return False
    def attracts(self, other): return 0.0

#----------------------------------------------------------------------------

class ParticleBody (Body):
    '''The simplest body has position and mass but no size or orientation.'''

    def __init__(self):
        super(ParticleBody, self).__init__()
        self.position = V()
        self.mass = 1

class RigidBody (ParticleBody):
    '''A physical body that has size and orientation but no flexibility.'''

    def __init__(self):
        super(RigidBody, self).__init__()
        self.orientation = Q()
        #TODO: inertial distribution of mass
        #TODO: circumscribed radius (radius of farthest matter)
        pass

class ComplexBody (Body):
    '''A multi-body system, such as particles. Bodies are independent.'''

    def __init__(self, *args):
        super(ComplexBody, self).__init__()
        self.particles = set([])
        for arg in args:
            self.particles.add(arg)

class SpringBody (ComplexBody):
    '''A two-body system, with a classic spring distance relationship.'''

    def __init__(self, this, that, ideal=1.0, stiff=1.0):
        super(SpringBody, self).__init__(this, that)
        self.ideal = ideal
        self.stiff = stiff

class ElasticBody (ComplexBody):
    '''A single body comprised of many spring-attached massive particles.'''

    def __init__(self, bodies, springs):
        super(ElasticBody, self).__init__()
        self.springs = set([])
        # need caller to offer list of spring pairs or a SpringBody per pair
        pass

#----------------------------------------------------------------------------

class ReferenceFrame (object):

    def visit(self, time):
        self.time = time
        self.bodies = {} # { body : [force,accel,torque] accumulator }

    # list of objects
    def advance(self, time):
        dt = time - self.time
        if zero(dt):
            return
        # for each body,
        #     accumulate forces
        # for each body,
        #     see if moving f=ma would collide before or at time
        # for each collision,
        #     figure actual time of each collision
        # recurse self.advance(time of earliest collision)
        # recurse self.advance(original target time)
        pass

    pass

#----------------------------------------------------------------------------

def __test__():
    from testing import __ok__
    print 'Testing physical simulation classes...'

if __name__ == '__main__':
    raise Exception, \
        'This module is not a stand-alone script.  Import it in a program.'