[PYTHON] First command plugin

Overview

Describes the contents of the Maya command plug-in for beginners.

--What is a command plugin? ――How can you use the command plug-in? ――What kind of reference article do you have?

motivation

You don't see much information about command plugins. By the way, I didn't use it at all ... So my aim is to write an introductory article for myself. Anyway, the content is light because I think I will increase the number of articles about Maya Python.

** What is a command plugin? ** **

Official Help says:

Define a new custom MEL command and respond accordingly add functions to the maya.cmds Python module so they can be used in scripts.

In short, you can call your own Python module directly from cmds.

** Command plugin to do cmds.ls (sl = True) **

Anyway, it's quick to write and use it. So, let's write the function of cmds.ls (sl = True) with a command plugin. The following code is based on (or copied) from Maya Help.

command_select.py

# -*- coding: utf-8 -*-
import maya.api.OpenMaya as OpenMaya


def maya_useNewAPI():
    pass

class CommandSelection(OpenMaya.MPxCommand):
    kPluginCmdName = "selection"

    def __init__(self):
        OpenMaya.MPxCommand.__init__(self)

    @staticmethod
    def cmdCreator():
        return CommandSelection()

    def doIt(self, args):
        self.setResult(list(OpenMaya.MGlobal.getActiveSelectionList().getSelectionStrings()))
 
def initializePlugin(mobject):
    plugin = OpenMaya.MFnPlugin(mobject)
    plugin.registerCommand(CommandSelection.kPluginCmdName, CommandSelection.cmdCreator)

def uninitializePlugin(mobject):
    pluginFn = OpenMaya.MFnPlugin(mobject)
    pluginFn.deregisterCommand(CommandSelection.kPluginCmdName)

command_select_doit.py

cmds.selection()
>>> # Result: [u'pPlane2', u'pPlane1'] # 

Code content

* About the return value *

The return value of the command is not a return statement! (Prejudice) When I check Help, it says setResult (), so I call it with doIt ().

When I tried to setResult () my own class to improve it a little, An error occurs with # Command results must be string or numeric.. I haven't investigated the case of other parent classes, but I wonder if the command plugin can only return strings or numbers.

* About the parent class *

Classes prefixed with> ** MPx ** are called proxy classes and are called proxy classes.

Used to create various plugin types.

So I looked at the Reference to see what other classes are available. Which parent should be inherited according to the plugin you want to make? I need more study.

** Impression **

If you use a command plug-in for processing that seems to be used very often, the amount of code will be reduced and it may be easier. It can also be used as a MEL command, so it may be useful for MELer artists. I would like to continue studying while waiting for advice and advice from various fields.

** Reference site **

-Digital Matrix Simple Plugin -Digital Matrix Command to check selected node -[Autodesk Knowledge Network: Command Plugin](https://knowledge.autodesk.com/en/support/maya/learn-explore/caas/documentation/MAYAUL/2014/JPN/Maya-API-Documentation/files/Command -plugins-htm.html)