Simple transparency example not working in Java 3D

Question

Hi all,

I'm a complete n00b in j3d (but an expert in Java). Just starting out, I'm running into a problem playing with transparency. I've got a simple example which draws a rotating planar quad (disappears when showing the back face because I haven't disabled backface culling).

With the Color3b and COLOR_3 lines uncommented (and the corresponding Color4b and COLOR_4 lines commented), I see the rotating quad, colored red.

However, when I comment the color-3 lines and uncomment the color-4 lines, I see a BLACK square (against the white background), even though the alpha value is set to 255 (fully opaque).

What am I doing wrong? Google doesn't help, and even the Java3D forum over at java.forums.net is less than helpful. StackOverflow, save me! You can copy and past the below program, run it and see what happens.

Here are my specs:

Java 6 on OSX 10.5.5 J3D 1.5.2 JOGL 1.1.1

Thanks,

--Rob

Here's the code:

import com.sun.j3d.utils.applet.MainFrame;
import com.sun.j3d.utils.geometry.ColorCube;
import com.sun.j3d.utils.universe.SimpleUniverse;
import java.applet.Applet;
import java.awt.*;
import javax.media.j3d.*;
import javax.vecmath.*;

public class Hello extends Applet
{
 public Hello() throws Exception
 {
  setLayout(new BorderLayout());
  GraphicsConfiguration config = SimpleUniverse.getPreferredConfiguration();
  Canvas3D canvas3D = new Canvas3D(config);

  add("Center", canvas3D);

  BranchGroup scene = createSceneGraph();
  scene.compile();

  SimpleUniverse univ = new SimpleUniverse(canvas3D);

  univ.getViewingPlatform().setNominalViewingTransform();

  univ.addBranchGraph(scene);
 }

 public BranchGroup createSceneGraph() throws Exception
 {
  BranchGroup root = new BranchGroup();

  // A white background.

  Background bgd = new Background(1.0f, 1.0f, 1.0f);
  root.addChild(bgd);

  // This will spin the quad around

  TransformGroup spin = new TransformGroup();
  spin.setCapability(TransformGroup.ALLOW_TRANSFORM_WRITE);
  root.addChild(spin);

  // define the quad:

  Point3d p1 = new Point3d(-0.5, -0.5, 0);
  Point3d p2 = new Point3d(0.5, -0.5, 0);
  Point3d p3 = new Point3d(0.5, 0.5, 0);
  Point3d p4 = new Point3d(-0.5, 0.5, 0);

  // colors

  Color4b c = new Color4b((byte)255, (byte)0, (byte)0, (byte)255);
  //Color3b c = new Color3b((byte)255, (byte)0, (byte)0);

  QuadArray quads = new QuadArray(4,
    GeometryArray.COORDINATES | GeometryArray.COLOR_4);
    // GeometryArray.COORDINATES | GeometryArray.COLOR_3);

  quads.setCoordinate(0, p1);
  quads.setCoordinate(1, p2);
  quads.setCoordinate(2, p3);
  quads.setCoordinate(3, p4);
  quads.setColor(0, c);
  quads.setColor(1, c);
  quads.setColor(2, c);
  quads.setColor(3, c);

  // Not sure if I need this. Doesn't seem to make a difference.

  Appearance appearance = new Appearance();
  TransparencyAttributes trans = new TransparencyAttributes();
  trans.setTransparencyMode(TransparencyAttributes.BLENDED);
  appearance.setTransparencyAttributes(trans);

  // Create the shape...

  Shape3D shape = new Shape3D();
  shape.setGeometry(quads);
  shape.setAppearance(appearance);

  spin.addChild(shape);

  Alpha rotationAlpha = new Alpha(-1, 4000);
  RotationInterpolator rotator = new RotationInterpolator(rotationAlpha, spin);
  BoundingSphere bounds = new BoundingSphere();
  rotator.setSchedulingBounds(bounds);
  spin.addChild(rotator);

  return root;
 }

 public static void main(String[] args) throws Exception
 {
  Frame frame = new MainFrame(new Hello(), 256, 256);
 }
}

Answer 1

Replacing Color4b with Color4f, worked for me. Replace corresponding lines in your code with the lines below,

Color color = new Color(255, 0, 0, 50);

Color4f c = new Color4f(color);
QuadArray quads = new QuadArray(4, 
           GeometryArray.COORDINATES | GeometryArray.COLOR_4);

I used AWT Color, found it easier to pass in all ColorNx() constructors, i.e. Color3b(), Color4b(), and Color4f() etc. You may use float arguments directly, if that feels natural to you. The actual fix is the use of Color4f, not the AWT thingy. Even using AWT Color didn't solve the issue with Color4b. Just go with Color4f, I don't see any problem.

My platform: Java Version "1.6.0_10", Java 3D 1.5.2, Core2 Duo, OpenSUSE 11.0, Intel G33 Graphics.