# Difference between revisions of "Particle System Constraints"

Particle Constraints prevent particles from passing through certain areas, such as brushes. The can also be user-defined, such as a 2-Dimensional plane.

## Collision via traces

Uses traces for checking collisions.

collision mode
Type of collision? Valid ranges not known
collision group
Known arguments are NONE and DEBRIS?
amount of bounce
Amount of bounce force to apply when a collision occurs.
amount of slide
Amount of sliding force applied to particles currently on a surface.
kill particle on collision
Destroys the particle when it collides with an object
brush only
If 1, the particle will collide only with brushes
trace accuracy tolerance
Amount of tolerance to use when calculating collisions. Higher values mean more tolerance, but less realistic collisions. Lower values mean more accurate collisions, most likely at the cost of additional calculations.

## Constrain distance to path between two control points

Keeps particles on a path between two control points. Internally determined control point only?

minimum distance
Minimum distance between the two control points. It's recommended to keep this at zero.
maximum distance
Maximum distance between the two control points. It needs to be equal or greater than the distance between the two control points, in order to work.
maximum distance middle
Maximum distance between start and the middle? Default value is -1 which means off?
maximum distance end
Maximum distance between middle and end point? Default value is -1 which means off?
travel time
Maximum time a particle can spend traveling between the two points?
random bulge
Random clumping of particles? (No idea)
start control point number
The starting control point number. 0 is recommended since it is the particle system's origin.
end control point number
The end control point number. Using the start control point number is NOT recommended, as the particles will just around. See this in order to make a control point.
bulge control 0=random 1=orientation of start pnt 2=orientation of end point
Pretty self explanatory, determines where to place the bulge
mid point position
Determines the middle of the path, in a decimal percentage. 0.5 is the middle, 1 is the end, 0 is the beginning?

## Prevent passing through a plane

Blocks particles from passing through an imaginary two-dimensional plane. Default settings make it at the bottom of the particle's origin.

global origin
Use global origin instead of particle origin? (Not recommended)
plane point
The 2nd Point to use to define the plane?
plane normal
3D vector that determines the angle of the plane (same concept as VPlane)

## Prevent passing through static part of world

Prevents passing through any static part of the world. I.e. prop_statics, brushes, etc