stretchbehavior.java

《Java 3D编程》的源代码

/**********************************************************
  Copyright (C) 2001 	Daniel Selman

  First distributed with the book "Java 3D Programming"
  by Daniel Selman and published by Manning Publications.
  http://manning.com/selman

  This program is free software; you can redistribute it and/or
  modify it under the terms of the GNU General Public License
  as published by the Free Software Foundation, version 2.

  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  The license can be found on the WWW at:
  http://www.fsf.org/copyleft/gpl.html

  Or by writing to:
  Free Software Foundation, Inc.,
  59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.

  Authors can be contacted at:
  Daniel Selman: [e-mail]

  If you make changes you think others would like, please 
  contact one of the authors or someone at the 
  www.j3d.org web site.
**************************************************************/

package org.selman.java3d.book.behaviortest;

import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;

import javax.media.j3d.*;
import javax.vecmath.*;

import com.sun.j3d.utils.applet.MainFrame;
import com.sun.j3d.utils.geometry.*;

// this class implements a more complex behavior.
// the behavior modifies the coordinates within a 
// GeometryArray based on simulated forces applied to
// the model. Forces are modeled as springs from the origin
// to every node. Every node has a mass, and hence an 
// acceleration. Pressing a key will increase the acceleration
// at each node, upsetting the force equilibrium at each vertex.
// The model will then start to oscillate in size as the springs
// have no "damping" effect.
//
// note: this is a very computationally expensive behavior!

public class StretchBehavior extends Behavior
{
	// the wake up condition for the behavior
	protected WakeupCondition			m_WakeupCondition = null;

	// the GeometryArray for the Shape3D that we are modifying
	protected GeometryArray				m_GeometryArray = null;

	// cache some information on the model to save reallocation
	protected float[]					m_CoordinateArray = null;
	protected float[]					m_LengthArray = null;
	protected float[]					m_MassArray = null;
	protected float[]					m_AccelerationArray = null;

		protected Vector3f 				m_Vector = null;


	// spring stiffness: Fspring = k.Le
	protected float					m_kSpringConstant = 1.3f;

		protected float					m_kAccelerationLossFactor = 0.985f;


	public StretchBehavior( GeometryArray geomArray )
	{
		// save the GeometryArray that we are modifying
		m_GeometryArray = geomArray;

		// set the capability bits that the behavior requires
		m_GeometryArray.setCapability( GeometryArray.ALLOW_COORDINATE_READ );
		m_GeometryArray.setCapability( GeometryArray.ALLOW_COORDINATE_WRITE );
		m_GeometryArray.setCapability( GeometryArray.ALLOW_COUNT_READ );

		// allocate an array for the model coordinates
		m_CoordinateArray = new float[ 3 * m_GeometryArray.getVertexCount( ) ];

		// retrieve the models original coordinates - this defines 
		// the relaxed length of the springs
		m_GeometryArray.getCoordinates( 0, m_CoordinateArray );

		// allocate an array to store the relaxed length 
		// of the springs from the origin to every vertex
		m_LengthArray = new float[ m_GeometryArray.getVertexCount( ) ];

		// allocate an array to store the mass of every vertex
		m_MassArray = new float[ m_GeometryArray.getVertexCount( ) ];

		// allocate an array to store the acceleration of every vertex
		m_AccelerationArray = new float[ m_GeometryArray.getVertexCount( ) ];

		// allocate a temporary vector
		m_Vector = new Vector3f( );

		float x = 0;
		float y = 0;
		float z = 0;

		for( int n = 0; n < m_CoordinateArray.length; n+=3 )
		{
			// calculate and store the relaxed spring length
			x = m_CoordinateArray[n];
			y = m_CoordinateArray[n+1];
			z = m_CoordinateArray[n+2];

				m_LengthArray[n/3] = (x * x) + (y * y) + (z * z);

			// assign the mass for the vertex
			m_MassArray[n/3] = (float) (50 + ( 5 * Math.random( )));
		}

		// create the WakeupCriterion for the behavior
		WakeupCriterion criterionArray[] = new WakeupCriterion[2];
		criterionArray[0] = new WakeupOnAWTEvent( KeyEvent.KEY_PRESSED );
		criterionArray[1] = new WakeupOnElapsedFrames( 1 );

		// save the WakeupCriterion for the behavior
		m_WakeupCondition = new WakeupOr( criterionArray );
	}

	public void initialize( )
	{
		// apply the initial WakeupCriterion
		wakeupOn( m_WakeupCondition );
	}

	public void processStimulus( java.util.Enumeration criteria )
	{
		// update the positions of the vertices - regardless of criteria
		float elongation = 0;
		float force_spring = 0;
		float force_mass = 0;
		float force_sum = 0;
		float timeFactor = 0.1f;
		float accel_sum = 0;		

		// loop over every vertex and calculate its new position
		// based on the sum of forces due to acceleration and the
		// spring.
		for( int n = 0; n < m_CoordinateArray.length; n+=3 )
		{
			m_Vector.x = m_CoordinateArray[n];
			m_Vector.y = m_CoordinateArray[n+1];
			m_Vector.z = m_CoordinateArray[n+2];

			// use squared lengths, as sqrt is costly
			elongation = m_LengthArray[n/3] - m_Vector.lengthSquared( );

			// Fspring = k.Le
			force_spring = m_kSpringConstant * elongation;
			force_mass = m_AccelerationArray[n/3] * m_MassArray[n/3];

			// calculate resultant force
			force_sum = force_mass + force_spring;

			// a = F/m
			m_AccelerationArray[n/3] = (force_sum / m_MassArray[n/3]) * m_kAccelerationLossFactor;
			accel_sum += m_AccelerationArray[n/3];

			m_Vector.normalize( );

			// apply a portion of the acceleration as change in coordinate.
			// based on the normalized vector from the origin to the vertex
			m_CoordinateArray[n] += m_Vector.x * timeFactor * m_AccelerationArray[n/3];
			m_CoordinateArray[n+1] += m_Vector.y * timeFactor * m_AccelerationArray[n/3];
			m_CoordinateArray[n+2] += m_Vector.z * timeFactor * m_AccelerationArray[n/3];
		}

		// assign the new coordinates
		m_GeometryArray.setCoordinates( 0, m_CoordinateArray );

		while( criteria.hasMoreElements( ) )
		{
			WakeupCriterion wakeUp = (WakeupCriterion) criteria.nextElement( );			

			// if a key was pressed increase the acceleration at the 
			// vertices a little to upset the equiblibrium
			if( wakeUp instanceof WakeupOnAWTEvent )
			{
				for( int n = 0; n < m_AccelerationArray.length; n++ )
					m_AccelerationArray[n] += 0.3f;
			}
			else
			{
				// otherwise, print the average acceleration
				System.out.print( "Average acceleration:\t" + accel_sum/m_AccelerationArray.length + "\n" );
			}
		}

		// assign the next WakeUpCondition, so we are notified again
		wakeupOn( m_WakeupCondition );
	}
}