Maya Python Plugin: Problems with creating a basic nurbs curve

Coding
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1

Dear community,

I have a lot of experience with Maya Python scripts, but am a n00b when it comes to plugin writing.

Eventually I want a node that generates 1000s of curves based on rules.
I’m still failing with the basics. This is an attempt to create a circle (with, shamefully, support of GPT and the very sparse resources when it comes to creating curves in plugins online):

import math
import maya.OpenMaya as OpenMaya
import maya.OpenMayaMPx as OpenMayaMPx

class NurbsCircleNode(OpenMayaMPx.MPxNode):
    kPluginNodeName = "nurbsCircleNode"
    kPluginNodeId = OpenMaya.MTypeId(0x00000125)

    aRadius = OpenMaya.MObject()
    aOutputCurve = OpenMaya.MObject()

    def __init__(self):
        OpenMayaMPx.MPxNode.__init__(self)

    @staticmethod
    def creator():
        return OpenMayaMPx.asMPxPtr(NurbsCircleNode())
    
    @staticmethod
    def initialize():
        nAttr = OpenMaya.MFnNumericAttribute()
        tAttr = OpenMaya.MFnTypedAttribute()

        NurbsCircleNode.aRadius = nAttr.create("radius", "in", OpenMaya.MFnNumericData.kFloat, 1.0)
        nAttr.setKeyable(True)
        nAttr.setWritable(True)
        nAttr.setStorable(True)

        NurbsCircleNode.aOutputCurve = tAttr.create("outputCurve", "outCurve", OpenMaya.MFnData.kNurbsCurve)
        tAttr.setWritable(False)
        tAttr.setStorable(False)

        NurbsCircleNode.addAttribute(NurbsCircleNode.aRadius)
        NurbsCircleNode.addAttribute(NurbsCircleNode.aOutputCurve)

        NurbsCircleNode.attributeAffects(NurbsCircleNode.aRadius, NurbsCircleNode.aOutputCurve)
        
        def compute(self, plug, dataBlock):
            if plug == NurbsCircleNode.aOutputCurve:
                input_value = dataBlock.inputValue(NurbsCircleNode.aRadius).asFloat()
        
                num_points = 101
                points = OpenMaya.MPointArray([OpenMaya.MPoint(math.cos(math.radians(i * 360.0)) * input_value,
                                                               math.sin(math.radians(i * 360.0)) * input_value,
                                                               0.0) for i in range(num_points)])
                circle_data = OpenMaya.MFnNurbsCurveData().create()
        
                circle_fn = OpenMaya.MFnNurbsCurve()
                status = OpenMaya.MStatus()
                
                knots = OpenMaya.MDoubleArray(num_points + 2, 0.0)
                for i in range(num_points + 2):
                    knots[i] = float(i)
                    
                circle_fn.create(points, knots, 1, OpenMaya.MFnNurbsCurve.kOpen, False, False, circle_data, status)

                output_curve_attr = dataBlock.outputValue(NurbsCircleNode.aOutputCurve)
                output_curve_attr.setMObject(circle_data)
                dataBlock.setClean(plug)
            else:
                return OpenMaya.kUnknownParameter

def initializePlugin(plugin):
    pluginFn = OpenMayaMPx.MFnPlugin(plugin)
    try:
        pluginFn.registerNode(NurbsCircleNode.kPluginNodeName, NurbsCircleNode.kPluginNodeId,
                              NurbsCircleNode.creator, NurbsCircleNode.initialize)
    except Exception as e:
        OpenMaya.MGlobal.displayError(f"Failed to register node: {NurbsCircleNode.kPluginNodeName}\n{e}")
        raise

def uninitializePlugin(plugin):
    pluginFn = OpenMayaMPx.MFnPlugin(plugin)
    try:
        pluginFn.deregisterNode(NurbsCircleNode.kPluginNodeId)
    except Exception as e:
        OpenMaya.MGlobal.displayError(f"Failed to deregister node: {NurbsCircleNode.kPluginNodeName}\n{e}")
        raise

The node can be created, but when i connect it to the create input of nurbs curve the result is empty. Perhapse compute doesnt get called, because print commands don’t show.
I use API 1, because API 2 produced many annoying errors.

Additional question: What is the best way to reload a plugin while developing? unloadplugin and then load again doesnt seem to do it…

Cheers!
Patrick

1 Like
2

I feel silly, the compute function had the wrong indentation, now I’m getting readable errors :slight_smile:

To whom it may concern - this is my small script for quickly testing the plugin. Includes a workaround, since the regular “unloadPlugin” command didnt work for some reason:

import maya.cmds as mc
def plugin_reload(plugin_path):
    mc.file(f = 1, new = 1)
    is_loaded = mc.pluginInfo(plugin_path, query=True, loaded=True)
    if is_loaded:
        mel.eval("unloadPluginWithCheck( \"%s\", true )"%plugin_path.replace('\\','/'))
        
    mc.loadPlugin(plugin_path)

def Py1NurbsCircleNode_test():
    plugin_path = r"C:\...."
    plugin_reload(plugin_path)
    
    pluginNode = mc.createNode('nurbsCircleNode')
    curveSh = mc.createNode('nurbsCurve')
    mc.connectAttr('%s.outputCurve'%pluginNode, '%s.create'%curveSh, f = 1)