Overview

Create collision detection using expression node.

It is created only with expression node of Maya standard function. No plug-in node or other installation is required.

Tested with :

Maya 2024 (Python3.10.8)

Maya 2023 (Python3.9.7)

Maya 2022 (Python3.7.7)

Maya 2020 (Python2.7.11)

Maya 2019 and below are not supported

Example of capsule collider :

Supported colliders

Infinite Plane
Sphere
Capsule
Capsule2 (radius individually)
Cuboid

Installation

Please do one of the following:

Copy the expCol directory into the C:\Users\<username>\Documents\maya\scripts.
Add the parent directory of expCol to PYTHONPATH environment variable.
Add the parent directory of expCol to PYTHONPATH in Maya.env.

Note
expCol module is required on rigging, but is not needed on animation.

Usage

Create Collider

from expCol import collider

collider.iplane()   # Infinite Plane
collider.sphere()   # Sphere
collider.capsule()  # Capsule
collider.capsule2() # Capsule2 (radius individually)
collider.cuboid()   # Cuboid

Create Detection

from expCol import detection

detection.create(
    'parent', 
    'input', 
    'output', 
    'controller', 
    colliders=collider_list, 
    groundCol=True, 
    scalable=False,
    radius_rate=None,
)


`parent`	str	Parent 'transform' or 'joint'.
`input`	str	Child 'transform' or 'joint' before correction.
`output`	str	Child 'transform' or 'joint' after correction.
`controller`	str	Any node to add attributes for control.
`colliders`	list, optional	List of collider names. Defaults to [].
`groundCol`	bool, optional	Add horizontal plane collision. Defaults to False.
`scalable`	bool, optional	Allow for parent scale of joint-chain and parent scale of colliders. Defaults to False.
`radius_rate`	float, optional	Rate at which radius and tip radius are interpolated, between 0 and 1. Defaults to None.

Note
For more information on parent, input and output, please click here.

If you just want to add an attribute to a controller, do the following. It is also called in detection.create.

detection.add_control_attr(
    'controller', 
    groundCol=True, 
    tip_radius=True
)

Example

Running the following code will create a sample joint, create a collider, and even create a detection.

from maya import cmds
from expCol import collider, detection

# Create sample joint chain
rootCtl = cmds.createNode('transform', n='rootCtl')
jointList = []
for i in range(5):
    jointList.append(cmds.joint(n='joint_{}'.format(i), p=[i*3,0,0]))
cmds.setAttr(rootCtl+'.ty', 5)

for i in range(len(jointList)-1):
    p = cmds.listRelatives(jointList[i], p=True)[0]
    pos1 = cmds.xform(jointList[i], q=True, ws=True, t=True)
    pos2 = cmds.xform(jointList[i+1], q=True, ws=True, t=True)
    prt = cmds.createNode('transform', n='parent_{}'.format(i), p=p)
    ipt = cmds.createNode('transform', n='input_{}'.format(i), p=p)
    out = cmds.createNode('transform', n='output_{}'.format(i), p=p)
    cmds.xform(prt, ws=True, t=pos1)
    cmds.xform(ipt, ws=True, t=pos2)
    cmds.xform(out, ws=True, t=pos2)
    cmds.aimConstraint(out, jointList[i], u=[0,0,1], wu=[0,0,1], wut='objectrotation', wuo=prt)

# Create Colliders
collider_list = []
collider_list.append(collider.iplane())
collider_list.append(collider.capsule())

# Create Detections
for i in range(len(jointList)-1):
    detection.create(
        'parent_{}'.format(i), 
        'input_{}'.format(i), 
        'output_{}'.format(i), 
        'rootCtl', 
        colliders=collider_list, 
        groundCol=True, 
        scalable=True,
        radius_rate=float(i)/float(len(jointList)-2)
    )

`groundCol` option

Setting groundCol to True adds an invisible horizontal collision. The height can be changed with the GroundHeight value.

`scalable` option

If scalable is set to True, the scale of the parent of the joint-chain or the parent of the collider is reflected.

scalable=True	scalable=False

`radius_rate` option

Interpolate radius and tip_radius by the radius_rate value. 0.0 matches radius and 1.0 matches tip_radius.

What are Parent, Input, and Output?


Parent	world position of the parent joint.
Input	world position of the child joint before correction.
Output	world position of the child joint after correction.

Each is just transform node, and there is no input connection to translate of Parent and Input.

Also, joint chain is not directly related to collision. It will be controlled by aim constraint or IK later.

If you have more than two joint chain, create the same node graph in the child hierarchy.
It's the same for all patterns like Capsule, Infinite plane, Sphere...

Note

A high Colision Iteration value increases the accuracy of collision detection, but it also increases the processing load.
A large number of detections can be very heavy.
The number of colliders cannot be changed after a detection (expression node) is created.

Processing time

Processing time per joint measured using maya's profiler.

Collider (Iteration:5)	Avg
sphere	32.57 us
iplane	33.70 us
capsule	39.27 us
capsule2	48.94 us
cuboid	50.30 us

Windows 11

Intel(R) Core(TM) i7-10700 CPU @ 2.90GHz

Maya 2024

kamilisa/maya_expressionCollision