Appearance Is Everything

Materials

Materials have five properties that enable you to specify how the object appears. There are four colors: Ambient, Emissive, Diffuse, and Specular. The fifth property is shininess, that you specify with a number.

Each color specifies what light is given off in a certain situation.

• Ambient color reflects light that been scattered so much by the environment that the direction is impossible to determine. This is created by an AmbientLight in Java 3D.
• Emissive color is given off even in darkness. You could use this for a neon sign or a glow-in-the-dark object
• Diffuse color reflects light that comes from one direction, so it's brighter if it comes squarely down on a surface that if it barely glances off the surface. This is used with a DirectionalLight.
• Specular light comes from a particular direction, and it tends to bounce off the surface in a preferred direction. Shiny metal or plastic have a high specular component. The amount of specular light that reaches the viewer depends on the location of the viewer and the angle of the light bouncing off the object.

Changing the shininess factor affects not just how shiny the object is, but whether it shines with a small glint in one area, or a larger area with less of a gleaming look.

For most objects you can use one color for both Ambient and Diffuse components, and black for Emissive (most things don’t glow in the dark). If it’s a shiny object, you would use a lighter color for Specular reflections. For example, the material for a red billiard ball might be:

// billiard ball

// ambient emissive diffuse specular shininess

// Material mat = new Material(red, black, red, white, 70f);

For a rubber ball, you could use a black or red specular light instead of white which would make the ball appear less shiny. Reducing the shininess factor from 70 to 0 would not work the way you might expect, it would spread the white reflection across the whole object instead of it being concentrated in one spot.

Texture

Materials make change the appearance of a whole shape, but sometimes even the shiniest objects can seem dull. By adding texture you can produce more interesting effects like marbling or wrapping a two-dimensional image around your object.

The TextureLoader class enables you to load an image to use as a texture. The dimensions of your image must be powers of two, for example 128 pixels by 256. When you load the texture you can also specify how you want to use the image. For example, RGB to use the color of the image or LUMINANCE to see the image in black and white.

After the texture is loaded, you can change the TextureAttributes to say whether you want the image to replace the object underneath or modulate the underlying color. You can also apply it as a decal or blend the image with the color of your choice.

If you are using a simple object like a sphere then you will also have to enable texturing by setting the "primitive flags". These can be set to Primitive.GENERATE_NORMALS + Primitive.GENERATE_TEXTURE_COORDS when you create the object.

In case this is starting to sound a bit complicated, here is an example. You can experiment with the texture settings in this example and compare the results. You can download the picture I used from http://www.java3d.org/Arizona.jpg or you can substitute a picture of your own.

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

import com.sun.j3d.utils.universe.*;

import com.sun.j3d.utils.image.*;

import javax.media.j3d.*;

import javax.vecmath.*;

import java.awt.Container;

public class PictureBall {

public PictureBall() {

   // Create the universe

   SimpleUniverse universe = new SimpleUniverse();

   // Create a structure to contain objects

   BranchGroup group = new BranchGroup();

   // Set up colors

   Color3f black = new Color3f(0.0f, 0.0f, 0.0f);

   Color3f white = new Color3f(1.0f, 1.0f, 1.0f);

   Color3f red = new Color3f(0.7f, .15f, .15f);

   // Set up the texture map

   TextureLoader loader = new TextureLoader("K:\\3d\\Arizona.jpg",

      "LUMINANCE", new Container());

   Texture texture = loader.getTexture();

   texture.setBoundaryModeS(Texture.WRAP);

   texture.setBoundaryModeT(Texture.WRAP);

   texture.setBoundaryColor( new Color4f( 0.0f, 1.0f, 0.0f, 0.0f ) );

   // Set up the texture attributes

   //could be REPLACE, BLEND or DECAL instead of MODULATE

    TextureAttributes texAttr = new TextureAttributes();

   texAttr.setTextureMode(TextureAttributes.MODULATE);

    Appearance ap = new Appearance();

    ap.setTexture(texture);

    ap.setTextureAttributes(texAttr);

    //set up the material

   ap.setMaterial(new Material(red, black, red, black, 1.0f));

   // Create a ball to demonstrate textures

   int primflags = Primitive.GENERATE_NORMALS +

   Primitive.GENERATE_TEXTURE_COORDS;

   Sphere sphere = new Sphere(0.5f, primflags, ap);

   group.addChild(sphere);

   // Create lights

   Color3f light1Color = new Color3f(1f, 1f, 1f);

    BoundingSphere bounds =

    new BoundingSphere(new Point3d(0.0,0.0,0.0), 100.0);

   Vector3f light1Direction = new Vector3f(4.0f, -7.0f, -12.0f);

   DirectionalLight light1

       = new DirectionalLight(light1Color, light1Direction);

    light1.setInfluencingBounds(bounds);

   group.addChild(light1);

   AmbientLight ambientLight =

      new AmbientLight(new Color3f(.5f,.5f,.5f));

   ambientLight.setInfluencingBounds(bounds);

   group.addChild(ambientLight);

   // look towards the ball

   universe.getViewingPlatform().setNominalViewingTransform();

   // add the group of objects to the Universe

   universe.addBranchGraph(group);

}

public static void main(String[] args) {

   System.setProperty("sun.awt.noerasebackground", "true");

   new PictureBall();

}

}

You can also set up three-dimensional textures, using shapes instead of a flat image. Unfortunately, these do not currently work very well across different platforms.

Special Effects

Look at the AppearanceTest example that comes with Java 3D for more effects you can use. For example you can display objects as wire-frames, display only the corners of an object and so on. You can even make objects transparent, with the following settings:

TransparencyAttributes t_attr =

   new TransparencyAttributes(TransparencyAttributes.BLENDED,0.5f,

TransparencyAttributes.BLEND_SRC_ALPHA,

TransparencyAttributes.BLEND_ONE);

ap.setTransparencyAttributes( t_attr );

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