TwistStripApp demonstrates back face culling
/*
* TwistStripApp.java 1.0 98/12/30
*
* Copyright (c) 1998 Sun Microsystems, Inc. All Rights Reserved.
*
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/*
* Getting Started with the Java 3D API written in Java 3D
*
* TwistStripApp.java demonstrates back face culling. A 'twisted strip' is a
* continuous surface with a two twists in it. (A Mobius strip has one twist)
* The Class Strip creates a surface using a TriangleStripArray. A twist strip
* is placed in a scene graph with a RotationInterpolator so the strip spins. As
* the strip spins, when the back faces of the individual triangles face the
* image plate, they disappear.
*
* One twisted strip is created using the inner class (Twist). This visual
* object is rendered as filled polygons. A second twist visual object is made
* from the same Geometry with a different Appearance to render as lines (only).
* The line-only strip helps to see where the filled polygon strip is.
*/
import java.applet.Applet;
import java.awt.BorderLayout;
import java.awt.Frame;
import javax.media.j3d.Alpha;
import javax.media.j3d.Appearance;
import javax.media.j3d.Background;
import javax.media.j3d.BoundingSphere;
import javax.media.j3d.BranchGroup;
import javax.media.j3d.Canvas3D;
import javax.media.j3d.Geometry;
import javax.media.j3d.PolygonAttributes;
import javax.media.j3d.RotationInterpolator;
import javax.media.j3d.Shape3D;
import javax.media.j3d.TransformGroup;
import javax.media.j3d.TriangleStripArray;
import javax.vecmath.Color3f;
import javax.vecmath.Point3d;
import com.sun.j3d.utils.applet.MainFrame;
import com.sun.j3d.utils.universe.SimpleUniverse;
public class TwistStripApp extends Applet {
/////////////////////////////////////////////////
//
// create Twist visual object
//
public class Twist extends Shape3D {
////////////////////////////////////////////
//
// create twist subgraph
//
public Twist() {
this.setGeometry(createGeometry());
this.setAppearance(createAppearance());
} // end of twist constructor
Geometry createGeometry() {
TriangleStripArray twistStrip;
Color3f blue = new Color3f(0.0f, 0.0f, 1.0f);
// create triangle strip for twist
int N = 80;
int stripCounts[] = { N };
twistStrip = new TriangleStripArray(
N,
TriangleStripArray.COORDINATES | TriangleStripArray.COLOR_3,
stripCounts);
double a;
int v;
for (v = 0, a = 0.0; v < N; v += 2, a = v * 2.0 * Math.PI / (N - 2)) {
twistStrip.setCoordinate(v, new Point3d(0.7 * Math.sin(a) + 0.2
* Math.cos(a), 0.3 * Math.sin(a), 0.7 * Math.cos(a)
+ 0.2 * Math.cos(a)));
twistStrip.setCoordinate(v + 1, new Point3d(0.7 * Math.sin(a)
- 0.2 * Math.cos(a), -0.3 * Math.sin(a), 0.7
* Math.cos(a) - 0.2 * Math.cos(a)));
twistStrip.setColor(v, blue);
twistStrip.setColor(v + 1, blue);
}
return twistStrip;
}
// create Appearance for Twist Strip
//
// this method creates the default Appearance for the
// twist strip. The commented line of code containting
// the setCullFace will fix the problem of half of the
// Twisted Strip disappearing.
Appearance createAppearance() {
Appearance twistAppear = new Appearance();
PolygonAttributes polyAttrib = new PolygonAttributes();
// polyAttrib.setCullFace(PolygonAttributes.CULL_NONE);
twistAppear.setPolygonAttributes(polyAttrib);
return twistAppear;
}
} // end of class Twist
/////////////////////////////////////////////////
//
// create scene graph branch group
//
public BranchGroup createSceneGraph() {
BranchGroup contentRoot = new BranchGroup();
// Create the transform group node and initialize it to the
// identity. Add it to the root of the subgraph.
TransformGroup objSpin = new TransformGroup();
objSpin.setCapability(TransformGroup.ALLOW_TRANSFORM_WRITE);
contentRoot.addChild(objSpin);
Shape3D twist = new Twist();
objSpin.addChild(twist);
// Duplicate the twist strip geometry and set the
// appearance of the new Shape3D object to line mode
// without culling.
// Add the POLYGON_FILLED and POLYGON_LINE strips
// in the scene graph at the same point.
// This will show the triangles of the original Mobius strip that
// are clipped. The PolygonOffset is set to prevent stitching.
PolygonAttributes polyAttrib = new PolygonAttributes();
polyAttrib.setCullFace(PolygonAttributes.CULL_NONE);
polyAttrib.setPolygonMode(PolygonAttributes.POLYGON_LINE);
polyAttrib.setPolygonOffset(0.001f);
Appearance polyAppear = new Appearance();
polyAppear.setPolygonAttributes(polyAttrib);
objSpin.addChild(new Shape3D(twist.getGeometry(), polyAppear));
Alpha rotationAlpha = new Alpha(-1, 16000);
RotationInterpolator rotator = new RotationInterpolator(rotationAlpha,
objSpin);
// a bounding sphere specifies a region a behavior is active
// create a sphere centered at the origin with radius of 1
BoundingSphere bounds = new BoundingSphere();
rotator.setSchedulingBounds(bounds);
objSpin.addChild(rotator);
// make background white
Background background = new Background(1.0f, 1.0f, 1.0f);
background.setApplicationBounds(bounds);
contentRoot.addChild(background);
// Let Java 3D perform optimizations on this scene graph.
contentRoot.compile();
return contentRoot;
} // end of CreateSceneGraph method of TwistStripApp
// Create a simple scene and attach it to the virtual universe
public TwistStripApp() {
setLayout(new BorderLayout());
Canvas3D canvas3D = new Canvas3D(null);
add("Center", canvas3D);
BranchGroup scene = createSceneGraph();
// SimpleUniverse is a Convenience Utility class
SimpleUniverse simpleU = new SimpleUniverse(canvas3D);
// This will move the ViewPlatform back a bit so the
// objects in the scene can be viewed.
simpleU.getViewingPlatform().setNominalViewingTransform();
simpleU.addBranchGraph(scene);
} // end of TwistStripApp constructor
// The following method allows this to be run as an application
public static void main(String[] args) {
System.out.println("TwistStripApp - Java 3D API version 1.1");
System.out.print("See \"Getting Started with the Java 3D API\"");
System.out.println(" (section 2.6)");
System.out.println("This program demonstrates back face culling.");
System.out.print("In this program two visual objects rotate, ");
System.out.println("one wireframe and one solid surface.");
System.out.print("The wire frame is visible only when components");
System.out.println(" of the surface are culled.");
Frame frame = new MainFrame(new TwistStripApp(), 256, 256);
} // end of main method of TwistStripApp
} // end of class TwistStripApp
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