simpleSpring/simpleSpring.cpp

//-
// ==========================================================================
// Copyright 2015 Autodesk, Inc.  All rights reserved.
//
// Use of this software is subject to the terms of the Autodesk
// license agreement provided at the time of installation or download,
// or which otherwise accompanies this software in either electronic
// or hard copy form.
// ==========================================================================
//+

// DESCRIPTION:
// 
// Produces the dependency graph node "simpleSpring".
//
// This node is an example of a spring node that calculates the spring
// behavior that Maya can use in a simulation.
//
// The example MEL script "simpleSpring.mel" shows how to create the node
// and appropriate connections to correctly establish a user defined spring law. 
//

#include <maya/MIOStream.h>
#include <math.h>

#include "simpleSpring.h"
#include <maya/MFnDependencyNode.h>
#include <maya/MFnNumericAttribute.h>


//=================================================================
// Implement your new attributes here if your node has.
// Here is an example code.
//=================================================================
MObject simpleSpring::aSpringFactor;


MTypeId simpleSpring::id( 0x80017 );


simpleSpring::simpleSpring()
:   factor(0.0)
{
}


simpleSpring::~simpleSpring()
{
}


void *simpleSpring::creator()
{
    return new simpleSpring;
}


MStatus simpleSpring::initialize()
//
//  Descriptions:
//      Initialize the node, attributes.
//
{
    MStatus status;

    MFnNumericAttribute numAttr;

    //=================================================================
    // Initialize your new attributes here. Here is an example.
    //=================================================================
    aSpringFactor = numAttr.create("springFactor","sf",MFnNumericData::kDouble);
    numAttr.setDefault( 1.0 );
    numAttr.setKeyable( true );
    status = addAttribute( aSpringFactor );
    McheckErr(status, "ERROR adding aSpringFactor attribute.\n");

    return( MS::kSuccess );
}


MStatus simpleSpring::compute(const MPlug& /*plug*/, MDataBlock& block)
//
//  Descriptions:
//      In this simple example, do nothing in this method. But get the
//      spring factor here for "applySpringLaw" to compute output force.
//
//  Note: always let this method return "kUnknownParameter" so that 
//  "applySpringLaw" can be called when Maya needs to compute spring force.
//
//  It is recommended to only override compute() to get user defined
//  attributes.
//
{
    // Get spring factor,
    //
    factor = springFactor( block );

    // Note: return "kUnknownParameter" so that Maya spring node can
    // compute spring force for this plug-in simple spring node.
    //
    return( MS::kUnknownParameter );
}


MStatus simpleSpring::applySpringLaw
(
    double /*stiffness*/, double /*damping*/, double restLength,
    double /*endMass1*/, double /*endMass2*/,
    const MVector &endP1, const MVector &endP2,
    const MVector &/*endV1*/, const MVector &/*endV2*/,
    MVector &forceV1, MVector &forceV2
)
//
//  Descriptions:
//      In this overridden method, the attribute, aSpringFactor, is used
//      to compute output force with a simple spring law.
//
//      F = - factor * (L - restLength) * Vector of (endP1 - endP2).
//
{
    MVector distV = endP1 - endP2;
    double L = distV.length();
    distV.normalize();

    double F = factor * (L - restLength);
    forceV1 = - F * distV;
    forceV2 = - forceV1;

    return( MS::kSuccess );
}


MStatus initializePlugin(MObject obj)
{
    MStatus status;
    MFnPlugin plugin(obj, PLUGIN_COMPANY, "3.0", "Any");

    status = plugin.registerNode( "simpleSpring", simpleSpring::id,
                            &simpleSpring::creator, &simpleSpring::initialize,
                            MPxNode::kSpringNode );
    if (!status) {
        status.perror("registerNode");
        return status;
    }

    return status;
}

MStatus uninitializePlugin(MObject obj)
{
    MStatus status;
    MFnPlugin plugin(obj);

    status = plugin.deregisterNode( simpleSpring::id );
    if (!status) {
        status.perror("deregisterNode");
        return status;
    }

    return status;
}