xpBullet Soft Body

The xpBullet Soft Body tag gives a flexible, bendy dynamic to any object, when interacting with other objects in the scene.

Many of the settings are identical to xpBullet Rigid Body and illustrations for them can be found in that page.

xpBullet Rigid Body

Dynamics tab

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xpBullet Soft Body tag Dynamics tab menu settings.

Enabled

Checking this box enables the tag.

If this box is unchecked, the object to which the tag is attached will not be checked for collisions with any particles.

Mode

Set as Soft Body, by default, this changes the type of dynamic system being used.

The other options are: Collider and Rigid Body.

Activate

Set as Immediate, by default, this setting determines when the dynamic system is activated.

The alternatives are: On Collision and After Time.

Time

Sets the frame from when the dynamic system becomes active, when Activate is set to After Time.

Speed Threshold

This setting is used when Activate is set to On Collision.

It dictates how fast a colliding object needs to be traveling, at the point of collision, for it to activate the object.

Bounce

Allows you to control the amount of bounce, on collision.

The bounce setting controls the speed with which the particle will rebound from the object.

A bounce of 100% means that the speed after hitting the object is the same as before hitting it.

Friction

Gives control over friction forces, on collision.

Friction will cause the rolling particles to come to a halt.

The higher the setting, the more quickly they stop.

Scatter

This will allow you to introduce a degree of random reflection, upon impact.

When bouncing from flat surface, the particles will rebound at a reflected angle which is correct for the angle at which the particle strikes the surface.

For example, if the particle hits the surface at an angle of 90 degrees to it, the particle will bounce back in a direction which is the exact reverse of its original course.

This is geometrically correct but not necessarily realistic.

Scatter causes a degree or spread or scatter when the particle stream rebounds from a surface.

Linear Velocity

You can use this parameter to give some initial velocity to the object along any of the desired axes, once animation begins.

Mode

Set as Relative, by default, this will allow you to set the Variation in percentages.

The alternative is Absolute, where you can set the Variation in centimetres.

Variation

Can be set in each axis by either a percentage of variation (Relative setting) or in centimetres (Absolute setting).

Angular Velocity

As with Linear Velocity, you can use this parameter to give some initial spin to the object around any of the desired axes.

Applies an initial velocity, by the degree set, giving a rotation, when the animation starts.

Mode

Set as Relative, by default, this will allow you to set the Variation in percentages.

The alternative is Absolute, where you can set the Variation in centimetres.

Variation

Can be set in each axis by either a percentage of variation (Relative setting) or in centimetres (Absolute setting).

World Coordinates

By default, both linear and angular velocities are set using the object’s local axis.

Activating this setting uses the world axis coordinates.

Linear Threshold

This setting is used, along with the Angular Threshold and Deactivation Time settings, to define when an object is considered to be in a ‘resting’ state.

If an object moves less than this amount, within the Deactivation Time, it will be considered resting.

Angular Threshold

If an object rotates less than this amount, within the Deactivation Time, it will be considered resting.

Deactivation Time

The time designated as after which an ‘active’ object is deemed as ‘resting’, dependent on the Linear Threshold and Angular Threshold values set.

Collision Margin

When a bullet object is in a ‘resting’ state, it will remain motionless until it becomes ‘active’ again.

It will become ‘active’ if another bullet object collides with it.

The Collision Margin adjusts the sensitivity of ‘resting objects’ to collisions.

Lower values will make it more likely to wake.

In most scenes, this setting can be left at the default value of 1cm.

Linear Factor

This setting acts a multiplier for the linear velocity of an object.

Angular Factor

This setting acts a multiplier for the angular velocity of an object

Set Initial State

Click this button to set the initial state of the object.

Clear Initial State

Click this button to clear the initial state of the object.

Particle tab

When the xpBullet Soft Body tag is placed on an xpEmitter, a Particle tab becomes available.

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xpBullet Soft Body tag Particle tab menu settings.

Rotation

Set as Particle, by default, this controls the degree of Rotation on the axis set.

The other options are: Tangential and Custom.

Particle

Particles will adhere to world settings from the xpEmitter during travel.

Tangential

Particles will now face the direction of travel.

Custom

Allows you to set a custom degree of rotation on the different axes, using the Rotation parameters.

Variation

Relative, by default, this sets a variation to the Rotation setting, in percentages.

The alternative is Absolute, which sets the variation in degrees.

Relative

The variation relative to the Rotation set.

Spin

Adds degrees of spin to the different axes.

Variation

Set as Relative, by default, this sets a variation to the Spin setting, in percentages.

The alternative is Absolute, which sets the variation in degrees.

Relative

The variation relative to the Spin value set.

Mass tab

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xpBullet Soft Body tag Mass tab menu settings.

Density Uses

Set as World Density, by default,

The alternative settings are: Custom Density and Custom Mass (and Particle Mass, when your tag is on an xpEmitter).

World Density

Gives all tagged objects the same density level.

Custom Density

Using this setting allows you to give individual scene objects a customized density, by using the Density parameter.

Custom Mass

The volume of the objects has a bearing on the mass, unless you select Custom Mass, which allows you to give individual scene objects a customized mass, by using the Mass parameter.

Particle Mass

Allows you to change the particle mass inside the Extended Data tab of your xpEmitter, by using the Mass parameter within the Physical Data tab.

Density

When Density Uses is set to Custom Density, this parameter sets the density level for your object.

Mass

When Density Uses is set to Custom Mass*,* this parameter sets the mass level for your object.

Center of Mass

When unchecked, the tag will use a central point on your object as the center of mass, for all simulation purposes.

Checking this box will allow you to offset this center of mass by the amounts set in the different axes of the Offset parameter.

Offset

When Center of Mass is checked, you can offset the object center of mass by values input in the different axes.

Collision tab

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xpBullet Soft Body tag Collision tab menu settings.

Child Objects

Set as Copy Tag to Children, by default, this sets the relationship the tag has with any children objects in the scene.

The other options are Ignore and Compound Object.

Copy Tag to Children

All children of the object are also subject to the dynamics set in the tag.

Ignore

Any child objects will ignore the tag settings.

Compound Object

The entirety of the object subject to the tag is seen as one, single object.

Generated Objects

Set as Individual Objects, by default,

The other options are: Compound Object, First Level and Second Level.

Collision Shape

Set as Auto, by default, with soft body simulations, the bullet system will intuitively select the Triangulated Mesh shape from the options available.

The other options are: Box, Sphere, Cylinder, Capsule, Convex Hull and Triangulated Mesh; you can manually select a different option for your collision shape should you prefer.

Along Axis

This setting allows you to decide the orientation of the collision shape, on the X, Y or Z axis.

Segments

Only available if the Collision Shape is set to Cylinder or Capsule, this setting allows you to increase or decrease the subdivisions on your collision shape.

Less segments will result in less calculations, therefore a faster simulation time.

More segments results in more calculations and a slower sim time but more accuracy when it comes to collisions between dynamic objects.

Shrink By

Use this setting to reduce the size of the collision shape of the object.

Full Hull

Only available when Collision Shape is set to Convex Hull or Auto (with certain shapes that necessitate the Convex Hull setting).

When enabled, this ensures that the collision shape is ‘wrapped’ around the collision object, whilst ensuring that the geometry is not intersected but also ignoring any indentations in the object.

Use Deformers

Checking this box will ensure that any deformers are taken into account, when the collision shape is generated.

Soft Body tab

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xpBullet Soft Body tag Soft Body tab menu settings.

Construction

Time Scale

This setting allows you to manipulate how xpBullet processes time.

Bend Constraints

Checked by default, this setting activates bend constraints.

More bend constraints means a stiffer, more rigid soft-body simulation.

Bend Distance

Bend Distance is the search distance for bend constraints.

Set as 2, by default, increasing this value will enable a larger search for viable points to link with bend constraints.

This will result in a less bendy soft body dynamic object.

This animation demonstrates the effect of the Bend Distance parameter, with a value of 1, 2 and 3 set from left to right, respectively.

Constraints

Linear Stiffness, Map

This setting alters the stiffness between the points of your mesh.

Vertex maps can be used to drive where the stiffer areas are.

In this scene, there is a contrast in the Linear Stiffness setting, from 0.5% (on the left), to 5% (in the middle) and finally 100% (on the right).

Volume Stiffness, Map

By comparison, this setting alters the stiffness of the space inside your collision object.

Again, a vertex map can be dropped into the Map field, to give direction on where the volume is stiffest.

Volume Conservation, Map, Pressure, Map

The Volume Conservation parameter works in conjunction with the Pressure parameter to control the space inside your collision object, maintaining the shape.

The Volume Conservation setting works to keep the volume inside the shape the same, following any collision, preventing deflation.

The Pressure setting alters the pressure within the collision object.

As with the other constraints settings, vertex maps can be used to fine-tune where the conservation and pressure are targeted.

This is the vertex map, which is used in the animation, on the right.

With the vertex map dropped in the Map field and the Pressure value set high, at 3000%, positive pressure is created where there are bright areas in the vertex map, driving the Torus upwards towards the collider Cylinder.

Properties

Damping

This setting controls the damping factor, applied to the overall motion of the soft body.

Position Iter

Increasing this parameter helps to retain the shape of your collision objects, giving more structural rigidity.

Contacts

The ‘hardness’ can be defined as the visual weight and energy that is transferred from one object to another during collision.

Contacts UI.png

Within the Soft Body tab, here are the parameters available in the Contacts drop-down section.

Rigid Hardness

Controls the hardness levels of rigid bodies in your scene.

This scene contains a Sphere with an xpBullet Soft Body tag and a Cube with a Rigid Body tag. This first animation has Rigid Hardness on the Sphere set at 50% on contact with the Cube.

With Rigid Hardness on the Sphere raised to 9000%, the frenetic energy transferred to the Soft Body dynamic object on contact is increased.

Kinetic Hardness

Controls the hardness levels of colliders in your scene.

By contrast to the above, these animations show the Kinetic Hardness on contact. In this animation it is only at 1%.

In this second scene, the Kinetic Hardness is raised to 1000%, causing greater damage to the soft body on collision.

Soft Hardness

Controls the hardness levels of soft bodies in your scene.

Soft Hardness on the Sphere is set at 20%, on contact between the two objects, in this first scene. Note: The Soft Hardness on the Torus is set at 100% for both of these scenes.

With Soft Hardness increased to 850%, again there is greater damage to the soft body object (the Sphere).

Anchor Hardness

Sets the hardness of the anchor (can be displayed from a setting in the Display tab) between objects in your scene.

In these two animations, the xpBulletConstraints dynamic object is creating a fixed constraint between the collider (Cube) and the soft body (Sphere). As explained in the Display tab section below, the Anchor Connection can be seen in yellow, the Source in red and the Target in green. With a lower Anchor Hardness value, the constraint is relaxed in this first scene.

This second scene sees the Anchor Hardness value raised to 100%, which is keeping the anchor constraint stiff.

Display tab

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xpBullet Soft Body tag Display tab menu settings.

AA Bounding Boxes, Color

When enabled, a bounding box (blue by default) will surround the object.

The collision engine uses adaptive bounds for the collisions.

Instead of testing every polygon in an object to see if a particle is colliding with it, the engine only tests relevant areas of the mesh.

It does this by dividing the mesh into smaller and smaller boxes until the area containing the correct polygon is found.

You can show the adaptive boxes as they are created by enabling this setting.

This can be useful if you have multiple colliders and you aren’t sure if particles are colliding with one of them.

The color can be changed in the Color setting.

Collision Shape Active, Color

When the box is checked, the object will be surrounded by a wireframe (pink by default).

This wireframe is the collision shape that is used to control the collisions in the dynamic simulations.

This color can also be changed in the Color setting.

Collision Shape Resting, Color

This color is displayed as a wireframe surround when the object reaches a resting position.

Again, this color (green, by default) can be changed.

Collision Shape Inactive, Color

When the object is inactive in the scene, the wireframe surround will be this color (yellow, by default).

This color can be changed using the Color setting.

Collision Shape Axis

Enabling this setting will draw an axis from the tagged object’s center of mass.

The length of these axes can be extended in the Length parameter, below.

Length

Sets the length of the axis points.

Anchors

Enabling this setting, allows visualization of the anchors, the source and target points between the xpBullet constraints.

Source

Sets the color for the anchor source points.

Target

Sets the color for the anchor target points.

Anchor Connection, Color

Check this box to establish a visible anchor connection between objects in your scene (this must be set up in xpBulletConstraints).

The color can be changed in the Color palette.