> From: Daniel Selman <[EMAIL PROTECTED]>
> Does anyone know what the effect of the:
> PolygonAttributes.setPolygonOffset(float polygonOffset)
>
> method is?
This sets offset to be applied to polygons to allow primitives to be drawn on
top of the polygons without z-buffer fighting. For example, this is commonly
used to allow drawing edges on polygons. See the documentation for
glPolygonOffset() if you have it.
The J3D 1.1 version of polygon offset uses a static offset, which means that
all polygons with the offset get moved away from the eye by the specified
offset. See the attached example. The offset needed to prevent the edges of
the sphere from being lost depends on the graphics board being used, I've seen
values from 30-1500 necessary to make it look right.
Java3D 1.2 will have an offset with static and dynamic factors. The dynamic
factor offsets polygons by an amount which depends on thier slope wrt the eye
vector. The greater the slope, the greater the offset. This has two
advantages: 1) smaller offsets can be used, since the dynamic offsetting gives
more offset to the polygons which need more; 2) the dynamic offset is more
constant across different graphics boards, so the same polygon offset values
should work for more boards.
Doug Gehringer
Sun Microsystems
/*
* @(#)PolygonOffset.java 1.48 99/05/20 14:07:00
*
* Copyright (c) 1996-1998 Sun Microsystems, Inc. All Rights Reserved.
*
* Sun grants you ("Licensee") a non-exclusive, royalty free, license to use,
* modify and redistribute this software in source and binary code form,
* provided that i) this copyright notice and license appear on all copies of
* the software; and ii) Licensee does not utilize the software in a manner
* which is disparaging to Sun.
*
* This software is provided "AS IS," without a warranty of any kind. ALL
* EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING ANY
* IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR
* NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN AND ITS LICENSORS SHALL NOT BE
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* INDIRECT, SPECIAL, CONSEQUENTIAL, INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER
* CAUSED AND REGARDLESS OF THE THEORY OF LIABILITY, ARISING OUT OF THE USE OF
* OR INABILITY TO USE SOFTWARE, EVEN IF SUN HAS BEEN ADVISED OF THE
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* This software is not designed or intended for use in on-line control of
* aircraft, air traffic, aircraft navigation or aircraft communications; or in
* the design, construction, operation or maintenance of any nuclear
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*/
import javax.swing.*;
import javax.swing.event.*;
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.event.*;
import java.awt.GraphicsConfiguration;
import com.sun.j3d.utils.applet.MainFrame;
import com.sun.j3d.utils.geometry.Sphere;
import com.sun.j3d.utils.universe.*;
import javax.media.j3d.*;
import javax.vecmath.*;
public class PolygonOffset extends JFrame implements ChangeListener {
JLabel sliderValueLabel;
PolygonAttributes solidPa;
public BranchGroup createSceneGraph() {
// Create the root of the branch graph
BranchGroup objRoot = new BranchGroup();
// Create the transform group node and initialize it to the
// identity. Enable the TRANSFORM_WRITE capability so that
// our behavior code can modify it at runtime. Add it to the
// root of the subgraph.
TransformGroup objTrans = new TransformGroup();
objTrans.setCapability(TransformGroup.ALLOW_TRANSFORM_WRITE);
objRoot.addChild(objTrans);
// Create a Sphere. We will display this as both wireframe and
// solid to make a hidden line display
// wireframe
Appearance wire = new Appearance();
PolygonAttributes wirePa = new PolygonAttributes(
PolygonAttributes.POLYGON_LINE,
PolygonAttributes.CULL_BACK,
0.0f);
wire.setPolygonAttributes(wirePa);
Sphere wireSphere = new Sphere(0.7f, wire);
objTrans.addChild(wireSphere);
// solid
Color3f red = new Color3f(1.0f, 0.0f, 0.0f);
ColoringAttributes solidCa = new ColoringAttributes(red,
ColoringAttributes.SHADE_FLAT);
Material solidMat = new Material();
solidMat.setLightingEnable(false);
Appearance solid = new Appearance();
solid.setMaterial(solidMat);
solid.setColoringAttributes(solidCa);
solidPa = new PolygonAttributes(
PolygonAttributes.POLYGON_FILL,
PolygonAttributes.CULL_BACK,
0.0f);
solidPa.setCapability(PolygonAttributes.ALLOW_OFFSET_WRITE);
solid.setPolygonAttributes(solidPa);
Sphere solidSphere = new Sphere(0.7f, solid);
objTrans.addChild(solidSphere);
// Create a new Behavior object that will perform the desired
// operation on the specified transform object and add it into
// the scene graph.
AxisAngle4f axisAngle = new AxisAngle4f(0.0f, 0.0f, 1.0f,
-(float)Math.PI / 2.0f);
Transform3D yAxis = new Transform3D();
Alpha rotationAlpha = new Alpha(-1, Alpha.INCREASING_ENABLE,
0, 0,
80000, 0, 0,
0, 0, 0);
RotationInterpolator rotator =
new RotationInterpolator(rotationAlpha, objTrans, yAxis,
0.0f, (float) Math.PI*2.0f);
BoundingSphere bounds =
new BoundingSphere(new Point3d(0.0,0.0,0.0), 100.0);
rotator.setSchedulingBounds(bounds);
objTrans.addChild(rotator);
// Have Java 3D perform optimizations on this scene graph.
objRoot.compile();
return objRoot;
}
public void stateChanged(ChangeEvent e) {
JSlider source = (JSlider)e.getSource();
if (!source.getValueIsAdjusting()) {
System.out.println("made it");
float offset = source.getValue();
solidPa.setPolygonOffset(offset);
sliderValueLabel.setText(Float.toString(offset));
}
}
public PolygonOffset() {
super("Polygon Offset");
JPanel contentPane = new JPanel();
contentPane.setLayout(new BorderLayout());
GraphicsConfiguration config =
SimpleUniverse.getPreferredConfiguration();
Canvas3D canvas = new Canvas3D(config);
canvas.setSize(800, 800);
contentPane.add(canvas, BorderLayout.CENTER);
setContentPane(contentPane);
// Create a simple scene and attach it to the virtual universe
BranchGroup scene = createSceneGraph();
SimpleUniverse u = new SimpleUniverse(canvas);
// This will move the ViewPlatform back a bit so the
// objects in the scene can be viewed.
u.getViewingPlatform().setNominalViewingTransform();
u.addBranchGraph(scene);
JPanel sliderPanel = new JPanel();
JLabel sliderLabel = new JLabel("Polygon Offset");
sliderPanel.add(sliderLabel);
JSlider offsetSlider = new JSlider(JSlider.HORIZONTAL, 0, 1500, 0);
offsetSlider.addChangeListener(this);
sliderPanel.add(offsetSlider);
sliderValueLabel = new JLabel("0.0");
sliderPanel.add(sliderValueLabel);
contentPane.add(sliderPanel, BorderLayout.SOUTH);
pack();
show();
}
//
// The following allows PolygonOffset to be run as an application
// as well as an applet
//
public static void main(String[] args) {
new PolygonOffset();
}
}
