My apologies for an earlier posting in which I said that setNormalFlip
wan't illuminating both sides of a polygon. After caful examination it
turns out it is illuminating both sides of a polygon but it is doing so in
a strange way.
My program creates two squares with normals pointing in opposite directions
and a light source shining down the X axis.
When the program is run, both sides of both squares respond to
illumination, but one square appears to be illuminated from the +ive X axis
the
other square appears to be illuminated from the -ive X axis. It doesn't
mater if I
use a directional light source or a point light source, the same thing
happens.
Is this supposed to happen?
Here is an example program to illustrate the problem. It has one
directional light shining in the -ive X direction. Notice that one the
squares illuminate as if the light sources were coming from opposite
directions.
// beginning of file
import java.applet.Applet;
import java.awt.BorderLayout;
import java.awt.event.*;
import java.awt.GraphicsConfiguration;
import com.sun.j3d.utils.applet.MainFrame;
//import com.sun.j3d.utils.geometry.ColorCube;
import com.sun.j3d.utils.universe.*;
import javax.media.j3d.*;
import javax.vecmath.*;
// an appearance class that sets all the attrubutes I believe are
// necessary to render two sided shaded polygons
class PCHAppearance extends Appearance{
Color3f PATCH_COLOR = new Color3f(0.3f,0.3f,1.0f);
public PCHAppearance(){
PolygonAttributes polyatt = new PolygonAttributes();
polyatt.setPolygonMode(PolygonAttributes.POLYGON_FILL);
polyatt.setCullFace(polyatt.CULL_NONE);
polyatt.setBackFaceNormalFlip(true);
setPolygonAttributes(polyatt);
RenderingAttributes ra = new RenderingAttributes();
ra.setDepthBufferEnable(true);
setRenderingAttributes(ra);
ColoringAttributes c = new ColoringAttributes();
c.setShadeModel(c.SHADE_FLAT);
c.setColor(PATCH_COLOR);
setColoringAttributes(c);
setMaterial( new Material(PATCH_COLOR, new Color3f(0.1f, 0.1f, 0.1f),
PATCH_COLOR, new Color3f(0.0f, 0.0f, 0.0f), 80.0f ));
}
}
public class HelloUniverse extends Applet {
static final int NUM_VERTS = 4;
// Create the root of the branch graph
public BranchGroup createSceneGraph() {
BranchGroup objRoot = new BranchGroup();
TransformGroup objTrans = new TransformGroup();
objTrans.setCapability(TransformGroup.ALLOW_TRANSFORM_WRITE);
objRoot.addChild(objTrans);
//------------------------------------
// Create a universal bounds for the light source, and behaviors
influence
BoundingSphere uniBounds = new BoundingSphere(new Point3d(0.0,0.0,0.0),
10 );
// Set up the global, ambient light
Color3f alColor = new Color3f(0.2f, 0.2f, 0.2f);
AmbientLight aLgt = new AmbientLight(alColor);
aLgt.setInfluencingBounds(uniBounds);
objRoot.addChild(aLgt);
// Set up the directional (infinite) light source
Color3f lColor1 = new Color3f(0.9f, 0.9f, 0.9f);
Vector3f lDir1 = new Vector3f(-1.0f, 0.0f, 0.0f);
DirectionalLight lgt1 = new DirectionalLight(lColor1, lDir1);
lgt1.setInfluencingBounds(uniBounds);
objRoot.addChild(lgt1);
// Set up a Point light source
// Color3f lColor1 = new Color3f(0.9f, 0.9f, 0.9f);
// Vector3f lDir1 = new Vector3f(1.0f, 1.0f, -1.0f);
// PointLight lgt1 = new PointLight(lColor1, new Point3f(5.0f, 0.0f,
0.0f), new Point3f(1.0f, 0.0f, 0.0f) );
// lgt1.setInfluencingBounds(uniBounds);
// objRoot.addChild(lgt1);
// ----------------------
// This section creates a pair of TriangleStripArrays
int[] strips = new int[1];
strips[0] = NUM_VERTS;
Point3f verts[] = new Point3f[NUM_VERTS];
Vector3f norms[] = new Vector3f[NUM_VERTS];
// set up patch 1
TriangleStripArray p1 = new TriangleStripArray(NUM_VERTS,
GeometryArray.COORDINATES | GeometryArray.NORMALS , strips);;
for(int i = 0; i < NUM_VERTS; i++){
verts[i] = new Point3f(0.0f, 0.0f, 0.0f);
norms[i] = new Vector3f(1.0f, 0.0f, 0.0f);
}
verts[0] = new Point3f(0.0f, 0.5f, 0.0f);
verts[1] = new Point3f(0.5f, 0.5f, 0.0f);
verts[2] = new Point3f(0.0f, 0.0f, 0.0f);
verts[3] = new Point3f(0.5f, 0.0f, 0.0f);
for(int i = 0; i < NUM_VERTS; i++){
norms[i] = new Vector3f(0.0f, 0.0f, 1.0f);
}
p1.setCoordinates(0,verts);
p1.setNormals(0, norms);
// set up patch 2 offset on the x axis with normals reversed
TriangleStripArray p2 = new TriangleStripArray(NUM_VERTS,
GeometryArray.COORDINATES | GeometryArray.NORMALS , strips);;
verts[0] = new Point3f(-0.5f, 0.0f, 0.0f);
verts[1] = new Point3f(0.0f, 0.0f, 0.0f);
verts[2] = new Point3f(-0.5f, -0.5f, 0.0f);
verts[3] = new Point3f(0.0f, -0.5f, 0.0f);
for(int i = 0; i < NUM_VERTS; i++){
norms[i] = new Vector3f(0.0f, 0.0f, -1.0f);
}
p2.setCoordinates(0,verts);
p2.setNormals(0,norms);
// create a pair of objects with Appearances
objTrans.addChild(new Shape3D(p1, new PCHAppearance()));
objTrans.addChild(new Shape3D(p2, new PCHAppearance()));
// ------------------------------
// Create rotation behavior
Transform3D yAxis = new Transform3D();
Alpha rotationAlpha = new Alpha(-1, Alpha.INCREASING_ENABLE,
0, 0,
4000, 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 HelloUniverse() {
setLayout(new BorderLayout());
GraphicsConfiguration config =
SimpleUniverse.getPreferredConfiguration();
Canvas3D c = new Canvas3D(config);
add("Center", c);
// Create a simple scene and attach it to the virtual universe
BranchGroup scene = createSceneGraph();
SimpleUniverse u = new SimpleUniverse(c);
u.getViewingPlatform().setNominalViewingTransform();
u.addBranchGraph(scene);
}
// The following allows HelloUniverse to be run as an application
// as well as an applet
public static void main(String[] args) {
new MainFrame(new HelloUniverse(), 256, 256);
}
}
// end of file
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