constrain_mpm

Use this compound to create constraints on the point_position of the source geometry that will be enforced during simulation. A constraint is a way to force certain points to travel according to the animated motion of either the input mpm_source geometry or the constraint_geometry. The position that a point is constrained to is called the target position. The constraint can either be hard, meaning deviation isn't allowed, or soft, meaning it acts as a guide to the motion (see the strength input). Note: You can constrain the source to stay still as well by providing input that doesn't move.

The mpm_source input should be connected to the cloth_source output of make_mpm_cloth, the fiber_source output of make_mpm_fiber, or the shell_source output of make_shell_fiber. The out_mpm_source output from this compound should be connected to the sources input of simulate_mpm. Multiple constrain_mpm compounds can also be chained together in between make_mpm_cloth and simulate_mpm. When conflicting constraints would apply to the same point the last constraint added overrides the previous constraints.

Inputs

mpm_source

The constraints will apply to any number of mpm_source that are attached. If no constraint_geometry are provided, the motion of the input geometry will be used to set the target position.

constraint_geometry

Any points of the mpm_source input geometry inside the bounds_shape of a constraint_geometry input will be constrained, to follow the relative transform of the constraint_geometry between the start_frame and the current frame. The transform can be calculated in one of two ways:

• If the constraint_geometry has a float4x4 property transform, that will be used.
• Otherwise, it will calculate the best fit relative scale, rotation and translation between the two geometries.

The points to be constrained will be determined on the start_frame of the source and will not be updated during the simulation. However, their target position and strength will be updated throughout the simulation.

enable_constraints

Whether any constraints should be added.

start_frame

The frame when the simulated source geometry should begin to be constrained.

use_end_frame

Whether to deactivate the constraints after the end_frame.

end_frame

The last frame that the simulated source geometry will be constrained, if use_end_frame is enabled.

strength

A strength of 0 corresponds to unconstrained and a value of 1 to a hard or absolute constraint. Fractional values indicate soft constraints — the source will behave as if attached by zero rest length springs.

use_color_set

Whether or not to use a color set property value to scale the strength of the constraint.

color_set_name

The name of the color set on the geometry of the input mpm_source. You can add a watchpoint to see the name and the type of the color set on the input geometry. Color the alpha, RGB or RGBA channels to map the color set to a float.

bounds_shape

Whether to use the axis-aligned bounding box or bounding sphere of the constraint_geometry inputs to determine which points should be constrained.