3D graphics for Java mobile devices, Part 2: M3G's retained mode

/*
 * Sample code for M3G article on IBM developerWorks.
 * http://www.ibm.com/developerworks/
 */

package m3gsamples2;

import javax.microedition.lcdui.*;
import javax.microedition.m3g.*;

/**
 * Sample that displays a simple cube with eight vertices. It has the same
 * output than VerticesSample form the first part but uses retained mode instead
 * of immediate mode.
 *
 * @author Claus Hoefele
 */
public class VerticesRetainedSample extends Canvas implements Sample
{
  /** The cube's vertex positions (x, y, z). */
  private static final byte[] VERTEX_POSITIONS = {
    -1, -1,  1,    1, -1,  1,   -1,  1,  1,    1,  1,  1,
    -1, -1, -1,    1, -1, -1,   -1,  1, -1,    1,  1, -1
  };

  /** Indices that define how to connect the vertices to build 
   * triangles. */
  private static int[] TRIANGLE_INDICES = {
    0, 1, 2, 3, 7, 1, 5, 4, 7, 6, 2, 4, 0, 1
  };

  /** Object that represents the 3D world. */
  private World _world;
  
  /** Graphics singleton used for rendering. */
  private Graphics3D _graphics3d;

  /**
   * Called when this sample is displayed.
   */
  public void showNotify()
  {
    init();
  }

  /**
   * Initializes the sample.
   */
  protected void init()
  {
    // Get the singleton for 3D rendering and create a World.
    _graphics3d = Graphics3D.getInstance();
    _world = new World();
    
    // Create vertex data.
    VertexBuffer cubeVertexData = new VertexBuffer();
    VertexArray vertexPositions = 
        new VertexArray(VERTEX_POSITIONS.length/3, 3, 1);
    vertexPositions.set(0, VERTEX_POSITIONS.length/3, VERTEX_POSITIONS);
    cubeVertexData.setPositions(vertexPositions, 1.0f, null);

    // Create the triangles that define the cube; the indices point to
    // vertices in VERTEX_POSITIONS.
    TriangleStripArray cubeTriangles = new TriangleStripArray(
        TRIANGLE_INDICES, new int[] {TRIANGLE_INDICES.length});
    
    // Create a Mesh that represents the cube.
    Mesh cubeMesh = new Mesh(cubeVertexData, cubeTriangles, new Appearance());
    _world.addChild(cubeMesh);

    // Create a camera with perspective projection.
    Camera camera = new Camera();
    float aspect = (float) getWidth() / (float) getHeight();
    camera.setPerspective(30.0f, aspect, 1.0f, 1000.0f);
    camera.setTranslation(0.0f, 0.0f, 10.0f);
    _world.addChild(camera);
    _world.setActiveCamera(camera);
  }

  /**
   * Renders the sample on the screen.
   *
   * @param graphics the graphics object to draw on.
   */
  protected void paint(Graphics graphics)
  {
    _graphics3d.bindTarget(graphics);
    _graphics3d.render(_world);
    _graphics3d.releaseTarget();
  }

  /**
   * Returns the <code>Displayable</code> used to display this sample.
   *
   * @return display
   */
  public Displayable getDisplayable()
  {
    return this;
  }

  /**
   * Returns the display name of this sample.
   *
   * @return name
   */
  public String getName()
  {
    return "Cube Vertices Retained";
  }
}