Quick and dirty example functions/UI to light link with USD in Python for Maya

maya_usd_light_link_basic_ui.py

"""Minimal example of how to 'light link' with USD in maya via a quick and dirty UI

Basically all the buttons behave in the way that anything that is valid for UsdLux.LightAPI
is considered to be a Light, anything else in your current selection is a target.

USD manages both an *Includes* relationship and *Excludes* relationship - the UI
basically exposes both to 'add', 'remove' or 'clear' these relationships for a given
light. When adding or removing all selected objects in your selection that are not
a light are processed as the target.

This UI currently always uses a light link collection named `lightLink`.

"""


import logging
from functools import partial

from PySide2 import QtWidgets
import shiboken2
import maya.OpenMayaUI as apiUI
from maya import cmds
import mayaUsd.ufe
from pxr import Usd, UsdLux


log = logging.getLogger(__name__)

def get_maya_main_window():
    """Get the Maya main window.
    
    Returns: 
        PySide2.QtWidgets.QWidget: Maya main window.
    """
    ptr = apiUI.MQtUtil.mainWindow()
    if ptr is not None:
        return shiboken2.wrapInstance(int(ptr), QtWidgets.QWidget)


def get_selected_prims():
    """Return selected Usd.Prim list from Maya's UFE selection
    
    Returns:
        list[Usd.Prim]: Selected prims
    """
    paths = cmds.ls(selection=True, ufeObjects=True, long=True, absoluteName=True)
    prims = []
    for path in paths:
        prim = mayaUsd.ufe.ufePathToPrim(path)
        if prim:
            prims.append(prim)
    return prims


def get_selected_lights_and_targets():
    """Return selected lights and targets in selection.
    
    Returns:
        tuple[list[Usd.Prim], list[Usd.Prim]]: 
            Two-tuple containing a list of list and a list of targets
    """
    
    lights = []
    targets = []
    for prim in get_selected_prims():
        
        is_light = bool(UsdLux.LightAPI(prim))
        if is_light:
            lights.append(prim)
        else:
            targets.append(prim)
            
    return lights, targets


def set_tip(widget, tip):
    """Set tooltip and status tip for a QWidget."""
    widget.setToolTip(tip)
    widget.setStatusTip(tip)
            
        
class UsdLightLinkUI(QtWidgets.QDialog):
    
    Add = 0
    Remove = 1
    Clear = 2
    
    def __init__(self, parent=None):
        super(UsdLightLinkUI, self).__init__(parent=parent)
        
        self.setWindowTitle("USD Light Link")
        
        layout = QtWidgets.QVBoxLayout(self)
        
        add_include = QtWidgets.QPushButton("Add selected")
        set_tip(add_include, "Add selected objects to the includes list of selected lights")
        
        remove_include = QtWidgets.QPushButton("Remove selected")
        set_tip(remove_include, "Remove selected objects from the includes list of selected lights")
        
        clear_includes = QtWidgets.QPushButton("Clear all")
        set_tip(clear_includes, "Clear the includes list for all selected lights")
        
        add_exclude = QtWidgets.QPushButton("Add selected")
        set_tip(add_exclude, "Add selected objects to the excludes list of selected lights")
        
        remove_exclude = QtWidgets.QPushButton("Remove selected")
        set_tip(remove_exclude, "Remove selected objects from the excludes list of selected lights")
        
        clear_excludes = QtWidgets.QPushButton("Clear all")
        set_tip(clear_excludes, "Clear the excludes list for all selected lights")
        
        layout.addWidget(QtWidgets.QLabel("<b>Include</b>"))
        layout.addWidget(add_include)
        layout.addWidget(remove_include)
        layout.addWidget(clear_includes)
        layout.addWidget(QtWidgets.QLabel("<b>Exclude</b>"))
        layout.addWidget(add_exclude)
        layout.addWidget(remove_exclude)
        layout.addWidget(clear_excludes)
        
        add_include.clicked.connect(partial(self.apply, action=self.Add, include=True))
        remove_include.clicked.connect(partial(self.apply, action=self.Remove, include=True))
        clear_includes.clicked.connect(partial(self.apply, action=self.Clear, include=True))
        add_exclude.clicked.connect(partial(self.apply, action=self.Add, exclude=True))
        remove_exclude.clicked.connect(partial(self.apply, action=self.Remove, exclude=True))
        clear_excludes.clicked.connect(partial(self.apply, action=self.Clear, exclude=True))
        
    def apply(self, action, include=False, exclude=False):
        lights, targets = get_selected_lights_and_targets()
        
        def _apply(relationship, targets, action):
            if action == self.Add:
                for target in targets:
                    relationship.AddTarget(target.GetPath())
            elif action == self.Remove:
                for target in targets:
                    relationship.RemoveTarget(target.GetPath())
            elif action == self.Clear:
                relationship.ClearTargets(True)
        
        for light in lights:
            print("Processing light:", light)
            collection = Usd.CollectionAPI(light, "lightLink")
            
            if include:
                includes = collection.GetIncludesRel()
                _apply(includes, targets, action)
                
            if exclude:
                excludes = collection.GetExcludesRel()
                _apply(excludes, targets, action)


        
maya_window = get_maya_main_window()
dialog = UsdLightLinkUI(parent=maya_window)
dialog.resize(200, 200)
dialog.show()
    

Written as example for Maya USD Light Link discussion here.