TYPE: POP
TITLE: Collision POP

The Collision POP performs collision detection of the particles on
some referenced SOP geometry. The Attributes tab is used to add attributes 
that store information about the particle's last collision. With the exception 
of the distance attribute, these attributes are not set unless a collision 
occurred. Local variables are usable in parameters denoted with a *.

This POP modifies the following attributes: accel, dist, hitCd, hitN, hitid, 
hitpos, hitposuv, hittime, hituv, numhit.

The particle state can later be queried using some of the following local
variables: DEAD, SLIDING, STOPPED, STUCK

Parameters:
    Activation              - Turns the POP on and off                /activate
    Source Group            - Subset of points to act on
Collision
    Geometry Source         - Specifies where the POP should get
                              the collision Object and SOP
    SOP                     - Collision SOP
    Ignore Transform Object - Transform geometry to transform object space
    Geometry Moves with Time   - Use collision algorithm which tries to
                                 take the motion of the object into account
    Collision Tolerance     - Distance from geometry at which particle is
                              considered to have collided            /tolerance
Behavior
    Behavior                - How particle behaves after collision 
    Collision Event         - Generate event when any point collides
    Collision Group         - Group to contain collided points
    Preserve Group          - Add particles to group instead of replacing
    Use as Hit ID           - How to set the Hit ID attribute
   *Hit Index               - Index as used in Hit ID                 /hitindex
    Oversampling            - Oversamples only the motion of the geometry
                              for more accurate collisions              /sample
    Bounce Accuracy         - Max # of inter-frame bounces to perform   /bounce
   *Gain Tangent            - Energy loss tangent to collision         /gaintan
   *Gain Normal             - Energy loss normal to collision          /gainnml
    Final Behavior          - How particle behaves after collision when
                              the impulse drops below the Minimum Impulse
   *Minimum Impulse         - Impulse below which to apply the default
                              behavior.                             /minimpulse
Attributes 
    Add Num Hit Attr           - Number of times collided             ($NUMHIT)
    Add Hit ID Attr            - Hit ID                                ($HITID)
    Add Hit Time Attr          - Time of collision                   ($HITTIME)
    Add Hit Position Attr      - Where collision occurred            ($HT{XYZ})
    Add Hit Position UV Attr   - Parametric collision position         ($H{UV})
    Add Hit Normal Attr        - Normal where collision occurred     ($HN{XYZ})
    Add Hit Diffuse Color Attr - Diffuse color at collision          ($HC{RGB})
    Add Hit Texture UV Attr    - Texture uv at collision           ($HMAP{UVW})
    Add Distance Attr          - Distance from current position to collision 
                                                                    ($DISTANCE)
Local Variables 
    Overview - The standard local variables are usable in this POP.  Please
               refer to the Houdini manual for more details.

See Also: Limit, SoftLimit
