3D graphics for Java mobile devices, Part 1: M3G's immediate mode

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

package m3gsamples1;

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

/**
 * Sample demonstrating depth buffer and projection.
 *
 * @author Claus Hoefele
 */
public class DepthBufferProjectionSample 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
  };

  /** The cube"s vertex data. */
  private VertexBuffer _cubeVertexData;

  /** The cube"s triangles defined as triangle strips. */
  private TriangleStripArray _cubeTriangles;

  /** Graphics singleton used for rendering. */
  private Graphics3D _graphics3d;

  /** Camera with perspective projection. */
  private Camera _cameraPerspective;

  /** The camera"s transformation. */
  private Transform _cameraTransform;

  /** Camera with parallel projection. */
  private Camera _cameraParallel;

  /** Flag whether perspective or parallel projection is used. */
  private boolean _isPerspective;

  /** Flag whether depth buffer is enabled. */
  private boolean _isDepthBufferEnabled;

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

  /**
   * Initializes the sample.
   */
  protected void init()
  {
    // Get the singleton for 3D rendering.
    _graphics3d = Graphics3D.getInstance();

    // Create vertex data.
    _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.
    _cubeTriangles = new TriangleStripArray(TRIANGLE_INDICES,
        new int[] {TRIANGLE_INDICES.length});

    // Create parallel and perspective cameras.
    _cameraPerspective = new Camera();
    float aspect = (float) getWidth() / (float) getHeight();
    _cameraPerspective.setPerspective(30.0f, aspect, 1.0f, 1000.0f);
    _cameraTransform = new Transform();
    _cameraTransform.postTranslate(0.0f, 0.0f, 10.0f);

    _cameraParallel = new Camera();
    _cameraParallel.setParallel(5.0f, aspect, 1.0f, 1000.0f);

    _graphics3d.setCamera(_cameraPerspective, _cameraTransform);
    _isPerspective = true;

    // Enable depth buffer.
    _isDepthBufferEnabled = true;
  }

  /**
   * Renders the sample on the screen.
   *
   * @param graphics the graphics object to draw on.
   */
  protected void paint(Graphics graphics)
  {
    // Create transformation objects for the cubes.
    Transform origin = new Transform();
    Transform behindOrigin = new Transform(origin);
    behindOrigin.postTranslate(-1.0f, 0.0f, -1.0f);
    Transform inFrontOfOrigin = new Transform(origin);
    inFrontOfOrigin.postTranslate(1.0f, 0.0f, 1.0f);

    // Disable or enable depth buffering when target is bound.
    _graphics3d.bindTarget(graphics, _isDepthBufferEnabled, 0);
    _graphics3d.clear(null);

    // Draw cubes front to back. If the depth buffer is enabled, 
    // they will be drawn according to their z coordinate. Otherwise,
    // according to the order of rendering.
    _cubeVertexData.setDefaultColor(0x00FF0000);
    _graphics3d.render(_cubeVertexData, _cubeTriangles,
        new Appearance(), inFrontOfOrigin);
    _cubeVertexData.setDefaultColor(0x0000FF00);
    _graphics3d.render(_cubeVertexData, _cubeTriangles,
        new Appearance(), origin);
    _cubeVertexData.setDefaultColor(0x000000FF);
    _graphics3d.render(_cubeVertexData, _cubeTriangles,
        new Appearance(), behindOrigin);

    _graphics3d.releaseTarget();

    drawMenu(graphics);
  }

  /**
   * Draws a menu on the screen.
   *
   * @param graphics graphics context.
   */
  protected void drawMenu(Graphics graphics)
  {
    graphics.setColor(0xFFFFFFFF);
    int fontHeight = graphics.getFont().getHeight();

    // Upper half menu.
    int height = 0;
    graphics.drawString(getKeyName(getKeyCode(FIRE)) + ": Reset",
        0, height, 0);

    // Lower half menu.
    height = getHeight() - fontHeight;
    if (_isDepthBufferEnabled)
    {
      graphics.drawString(getKeyName(getKeyCode(GAME_B)) +
          ": Depth Buffer: on", 0, height, 0);
    }
    else
    {
      graphics.drawString(getKeyName(getKeyCode(GAME_B)) +
          ": Depth Buffer: off", 0, height, 0);
    }

    height -= fontHeight;
    if (_isPerspective)
    {
      graphics.drawString(getKeyName(getKeyCode(GAME_A)) +
          ": Projection: perspective", 0, height, 0);
    }
    else
    {
      graphics.drawString(getKeyName(getKeyCode(GAME_A)) +
          ": Projection: parallel", 0, height, 0);
    }
  }

  /**
   * Handles key presses.
   *
   * @param keyCode key code.
   */
  protected void keyPressed(int keyCode)
  {
    switch (getGameAction(keyCode))
    {
      case GAME_A:
        _isPerspective = !_isPerspective;
        if (_isPerspective)
        {
          _graphics3d.setCamera(_cameraPerspective, _cameraTransform);
        }
        else
        {
          _graphics3d.setCamera(_cameraParallel, _cameraTransform);
        }
        break;

      case GAME_B:
        _isDepthBufferEnabled = !_isDepthBufferEnabled;
        break;

      case FIRE:
        init();
        break;

      // no default
    }

    repaint();
  }

  /**
   * 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 "Depth Buffer and View Projection";
  }
}