Constraints Object

Before using the Constraints object for the first time please read the section 'Using the Constraints object' at the bottom of this page.

Interface

The object's interface has several tabs:

Each tab is shown in its own section below.

For the 'Groups Affected' and 'Falloff' tabs, and for the buttons at the bottom of the interface, please see the 'Common interface elements' page.

Connections tab

Birth quicktab

Connect at Birth

If checked, makes a connection between a particle when it is born and any other particle, subject to the settings such as Connection Limit and Radius.

Weight

See 'Using the Constraints object' below.

Only Born

If checked, only makes connections between particles born at the same time.

Only Same Group

Connections will only be made between particles in the same group. But see 'Polygon Edges, 'Polygon Diag' below for a caveat to this switch.

Polygon Edges, Polygon Diag

These switches enable the particles to follow a cloth-like behaviour without the need for the overhead of Cloth FX. To use them, emit particles from an object such as a Plane object, turn on these switches, and also turn on collision in the Collisions tab. Then the particles will behave like this:

The particles are connected at birth along the polygon edges and/or diagonals, giving a more formal structure than the usual connections at birth.

if you have checked one or both of these switches, the formation of constraints along edges (and/or diagonals) takes priority over the 'Only Same Group' switch. In other words, if an edge has particles from different groups at each end of the edge, and 'Polygon Edges' is checked, a connection will be made between the two particles even if the 'Only Same Group' switch is checked.

Stiffness

This is a measure of how "strong" the connection is. Note that for stiffer connections it can give more predictable results to have a lower 'Stiffness' value and higher iterations and/or subframes (see the X-Particles project settings). A very high stiffness can cause unstable solving.

The stiffness settings can be expanded by clicking the little arrow to the left of the word 'Stiffness' to show a control spline and other settings:

These settings are:

Map to Param

The value from the 'Map' spline is mapped to the parameter chosen from this drop-down. For example, if the drop-down is set to 'Radius' particles with a small radius take the value from the left of the spline, while those with a larger radius take it from the right of the spline. This is a percentage value which is then multiplied with the 'Stiffness' setting to produce the final result.

The parameters which can be mapped are:

Temperature
Mass
Age
Radius
Speed

Min, Max

These are the minimum and maximum values from the mapped parameter. For example, if 'Radius' is mapped then a minimum value of zero means that particles with a radius of zero take the mapped value from the extreme left of the spline, while particles with a radius of 100 or more take the spline value from the extreme right of the spline.

Map

The control spline to which the selected parameter is mapped.

Connection Limit

This is a limit on the number of connections each particle can make. Keep this as low as possible, as too many connections can dramatically slowdown playback in the scene.

Min Dist

This setting limits the connections made to particles which are further away than this distance. This helps to control clumping so that particles don't just connect to the very closest ones.

Radius

The distance between particles must be less than this value for a connection to be made.

Break As

This drop-down controls how the link should break. A broken link means that there is no longer a connection between the particles. It has four options:

None

Connections will not break if this option is selected.

Relative Connected

The value in 'Break' is a percentage value of the distance when the particles were connected.

Relative Radius

The value in 'Break' is a percentage value of the distance in 'Radius'.

Absolute

'Break is an absolute distance setting and connections will break when they are longer than the 'Break Above' value.

Break, Break Above

A measure of how much the connection can stretch before it breaks. 0% means that the connection will never break. 50% means that it will break when it has stretched by 50% of its original length. When 'Break As' is set to 'Absolute' this changes to a distance measurement (labelled 'Break Above'), rather than a percentage. In this case the connection will break when it is longer than this value.

Note that the 'original length' is the length of the connection at the moment it is made. The actual length is relative to the particle radius. For example, a particle with a radius of 10 units will make a connection that is 10 units long but for a particle with a radius of 2 units the connection will be 2 units long.. This can then be stretched if the particle moves away from the surface and will break when stretched more than the percentage given in the 'Break' setting.

Distance quicktab

Connect Within Distance

If this switch is checked, connections will be made between particles within the distance specified in 'Radius'.

Only Same Group

Connections will only be made between particles in the same group.

Break

With the Distance connections, 'Break' behaves in the same way as 'Relative Connected' in the 'Birth' connections section.

Other parameters

The other parameters in this section work in exactly the same way as in the 'Birth' section, including the additional settings if you click the little arrow next to the label 'Stiffness'.

Custom quicktab

Custom

With this connection type you can set the parameters manually so as to connect and disconnect particles dynamically.

Only Same Group, Weight, Connection Limit and Radius

See the parameters with the same name in the 'Birth' section.

Compression section

Compression

This is the stiffness when the link (the connecting 'spring') is compressed.

Falloff

This drop-down controls how the stiffness falls off over the 'Radius' value. It has four possible settings:

Flat
Linear
Quadratic
Cubic

Break

This is an absolute distance; it represents the distance below which the connection will break.

Plastic

Below this distance the connection becomes 'plastic' - that is, it will no longer try to spring back to its original length, it has been deformed too much. Note that the stored length of the constraint changes depending on the 'Rate' value.

Rate

This is the rate at which the link becomes plastic (fixes to the new distance between the particles as they move in the scene).

Expansion section

Expansion

This is the stiffness of the link if the distance between the connected particles is greater than its connection distance (how far apart they were when linked).

Falloff, Break, Plastic and Rate

See the parameters with the same name in the 'Compression' section.

Collisions tab

This tab provides very simple particle to particle collisions but is much faster than the P-P Collision object and solves as part of the constraint. In other words, the collision can be a condition to the final solution of the constraint and not just an absolute value.

Collisions

Check this switch to enable collision constraints.

Stiffness

This controls how stiff the collision is. Essentially a dynamic 'spring' is created to keep the particles apart (from intersecting).

Group

This drop-down menu has three options:

All

Collisions between particles will occur regardless of what group the particles are in.

Same Group

Collisions will only occur between particles in the same group.

Different Groups

Collisions will only occur between particles in different groups.

Same Emitter

If this switch is checked, collisions will take place between particles emitted from the same emitter and between particles from different emitters. If it is unchecked, collisions will only take place between particles emitted from different emitters.