Simple collision detection node network for Maya

simple_collisions.py

from maya import cmds


def simple_collision_check(obj_xform, collider_shape):
    '''
    Create a node network that checks whether an objects xform is colliding with a mesh. Returns a condition node where outputX, Y, and Z are 1
    for colliding and 0 when not colliding.

    :param obj_xform: Path to object transform
    :param collider_shape: Path to mesh transform
    '''

    # Create nodes
    pnt_mat_mult = cmds.createNode('pointMatrixMult', name='obj_to_ws#')
    closest_pnt = cmds.createNode('closestPointOnMesh')
    minus = cmds.createNode('plusMinusAverage', name='ray_dir#')
    dot_product = cmds.createNode('vectorProduct', name='R_dot_N#')
    condition = cmds.createNode('condition', name='is_colliding#')

    # Object xform to world space
    cmds.connectAttr(obj_xform + '.parentMatrix[0]', pnt_mat_mult + '.inMatrix')
    cmds.connectAttr(obj_xform + '.translate', pnt_mat_mult + '.inPoint')

    # Nearest point on collider mesh
    cmds.connectAttr(pnt_mat_mult + '.output', closest_pnt + '.inPosition')
    cmds.connectAttr(collider_shape + '.worldMatrix', closest_pnt + '.inputMatrix')
    cmds.connectAttr(collider_shape + '.worldMesh[0]', closest_pnt + '.inMesh')

    # Direction to collider mesh
    cmds.setAttr(minus + '.operation', 2) # Operation 2 is Subtract
    cmds.connectAttr(closest_pnt + '.position', minus + '.input3D[0]')
    cmds.connectAttr(pnt_mat_mult + '.output', minus + '.input3D[1]')

    # Direction dot collider normal (Angle between mesh normal and xform)
    cmds.setAttr(dot_product + '.operation', 1) # Operation 1 is Dot Product
    cmds.setAttr(dot_product + '.normalizeOutput', 1) # Ensure value -1 to 1
    cmds.connectAttr(closest_pnt + '.normal', dot_product + '.input1')
    cmds.connectAttr(minus + '.output3D', dot_product + '.input2')

    # Check angle for collision
    # Dot product > 0 is a collision
    cmds.setAttr(condition + '.operation', 2) # Operation 2 is Greater Than
    cmds.setAttr(condition + '.colorIfTrue', 1, 1, 1)
    cmds.setAttr(condition + '.colorIfFalse', 0, 0, 0)
    cmds.connectAttr(dot_product + '.outputX', condition + '.firstTerm')

    return condition


def hide_on_collide(obj_xform, collider_xform):
    '''
    Hide a transform when colliding with a mesh.

    :param obj_xform: Path to a transform node
    :param collider_xform: Path to a meshes transform node
    '''

    collider_xform = cmds.listRelatives(
        collider_xform,
        shapes=True,
        type='mesh',
        noIntermediate=True
    )[0]

    # Create nodes
    condition = simple_collision_check(obj_xform, collider_xform)
    vis_condition = cmds.createNode('reverse', name='vis_condition#')

    cmds.connectAttr(condition + '.outColor', vis_condition + '.input')
    cmds.connectAttr(
        vis_condition + '.outputX',
        obj_xform + '.visibility',
        force=True
    )


def hide_on_collide_selected():
    '''
    Hides transforms when colliding with a mesh. Select some transforms
    then a collision mesh.
    '''

    xforms = cmds.ls(sl=True, long=True, transforms=True)
    if len(xforms) < 2:
        cmds.warning('Select multiple transforms then a collider mesh')
        return

    obj_xforms = xforms[:-1]
    collider_xform = xforms[-1]
    for obj_xform in obj_xforms:
        hide_on_collide(obj_xform, collider_xform)


if __name__ == '__main__':
    hide_on_collide_selected()