# Copyright (c) Niklas Rosenstein 2011
# Example of a gravitiy modifier for Cinema 4Ds
# Thinking Particles

import  c4d
import  c4d.documents                   as docs
import  c4d.modules.thinkingparticles   as c4dtp

# constants
GRAVITY         = 9.81      # m / (s ^ 2)
STORAGE         = type('', (), {}) () # Stores important data
STORAGE.frame   = 0

# functions
def main():

    doc     = docs.GetActiveDocument()
    fps     = doc.GetFps()
    frame   = doc.GetTime().GetFrame( fps )

    # check if the frame has changed
    try:
        if STORAGE.frame == frame:
            return
    finally:
        STORAGE.frame = frame

    direct  = op.GetMg().v3 * GRAVITY * 10 / fps
    tp      = doc.GetParticleSystem()

    for i in xrange( tp.NumParticles() ):
        vel = tp.Velocity( i )
        vel = vel + direct
        tp.SetVelocity(i, vel)

main()