/*
 * Portions Copyright (C) 2003 Sun Microsystems, Inc.
 * All rights reserved.
 */

/*
 *
 * COPYRIGHT NVIDIA CORPORATION 2003. ALL RIGHTS RESERVED.
 * BY ACCESSING OR USING THIS SOFTWARE, YOU AGREE TO:
 *
 *  1) ACKNOWLEDGE NVIDIA'S EXCLUSIVE OWNERSHIP OF ALL RIGHTS
 *     IN AND TO THE SOFTWARE;
 *
 *  2) NOT MAKE OR DISTRIBUTE COPIES OF THE SOFTWARE WITHOUT
 *     INCLUDING THIS NOTICE AND AGREEMENT;
 *
 *  3) ACKNOWLEDGE THAT TO THE MAXIMUM EXTENT PERMITTED BY
 *     APPLICABLE LAW, THIS SOFTWARE IS PROVIDED *AS IS* AND
 *     THAT NVIDIA AND ITS SUPPLIERS DISCLAIM ALL WARRANTIES,
 *     EITHER EXPRESS OR IMPLIED, INCLUDING, BUT NOT LIMITED
 *     TO, IMPLIED WARRANTIES OF MERCHANTABILITY  AND FITNESS
 *     FOR A PARTICULAR PURPOSE.
 *
 * IN NO EVENT SHALL NVIDIA OR ITS SUPPLIERS BE LIABLE FOR ANY
 * SPECIAL, INCIDENTAL, INDIRECT, OR CONSEQUENTIAL DAMAGES
 * WHATSOEVER (INCLUDING, WITHOUT LIMITATION, DAMAGES FOR LOSS
 * OF BUSINESS PROFITS, BUSINESS INTERRUPTION, LOSS OF BUSINESS
 * INFORMATION, OR ANY OTHER PECUNIARY LOSS), INCLUDING ATTORNEYS'
 * FEES, RELATING TO THE USE OF OR INABILITY TO USE THIS SOFTWARE,
 * EVEN IF NVIDIA HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
 *
 */

package demos.vertexArrayRange;

import demos.common.Demo;
import demos.common.DemoListener;
import java.awt.BorderLayout;
import java.awt.Frame;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;
import java.nio.IntBuffer;
import javax.media.opengl.GLProfile;
import javax.media.opengl.GL;
import javax.media.opengl.GL2ES1;
import javax.media.opengl.GL2;
import javax.media.opengl.GLAutoDrawable;
import javax.media.opengl.awt.GLCanvas;
import javax.media.opengl.glu.GLU;
import com.jogamp.opengl.util.Animator;
import javax.swing.JOptionPane;



/** <P> A port of NVidia's [tm] Vertex Array Range demonstration to
    OpenGL[tm] for Java[tm] and the Java programming language. The
    current web site for the demo (which does not appear to contain
    the original C++ source code for this demo) is <a href =
    "http://developer.nvidia.com/view.asp?IO=Using_GL_NV_fence">here</a>. </P>

    <P> This demonstration requires the following:

    <ul>
    <li> A JDK 1.4 implementation
    <li> an NVidia GeForce-based card
    <li> a recent set of drivers
    </ul>

    </P>

    <P> This demonstration illustrates the effective use of the
    java.nio direct buffer classes in JDK 1.4 to access memory outside
    of the Java garbage-collected heap, in particular that returned
    from the NVidia-specific routine wglAllocateMemoryNV. This memory
    region is used in conjunction with glVertexArrayRangeNV. </P>

    <P> On a 750 MHz PIII with an SDRAM memory bus and a GeForce 256
    running the Java HotSpot[tm] Client VM and OpenGL for Java 2.8,
    this demonstration attains 90% of the speed of the compiled C++
    code, with a frame rate of 27 FPS, compared to 30 FPS for the C++
    version. On higher-end hardware (a dual 667 MHz PIII with RDRAM
    and a GeForce 2) the demo currently attains between 65% and 75% of
    C++ speed with the HotSpot Client and Server compilers,
    respectively. </P> */

public class VertexArrayRange extends Demo {
  public static void main(String[] args) {
    // set argument 'NotFirstUIActionOnProcess' in the JNLP's application-desc tag for example
    // <application-desc main-class="demos.j2d.TextCube"/>
    //   <argument>NotFirstUIActionOnProcess</argument> 
    // </application-desc>
    boolean firstUIActionOnProcess = 0==args.length || !args[0].equals("NotFirstUIActionOnProcess") ;
    GLProfile.initSingleton(firstUIActionOnProcess);

    boolean startSlow = false;

    if (args.length > 1) {
      usage();
    }

    if (args.length == 1) {
      if (args[0].equals("-slow")) {
        startSlow = true;
      } else {
        usage();
      }
    }

    GLCanvas canvas = new GLCanvas();
    VertexArrayRange demo = new VertexArrayRange();
    if (startSlow) {
      demo.setFlag('v', false);   // VAR off
    }
    canvas.addGLEventListener(demo);

    final VertexArrayRange f_demo = demo;
    canvas.addKeyListener(new KeyAdapter() {
        public void keyTyped(KeyEvent e) {
          f_demo.dispatchKey(e.getKeyChar());
        }
      });


    final Animator animator = new Animator(canvas);
    animator.setRunAsFastAsPossible(true);
    demo.setDemoListener(new DemoListener() {
        public void shutdownDemo() {
          runExit(animator);
        }
        public void repaint() {}
      });

    Frame frame = new Frame("Very Simple NV_vertex_array_range demo");
    frame.addWindowListener(new WindowAdapter() {
        public void windowClosing(WindowEvent e) {
          runExit(animator);
        }
      });
    frame.setLayout(new BorderLayout());
    canvas.setSize(800, 800);
    frame.add(canvas, BorderLayout.CENTER);
    frame.pack();
    frame.setVisible(true);
    canvas.requestFocus();

    animator.start();
  }

  private static void usage() {
    System.out.println("usage: java VertexArrayRange [-slow]");
    System.out.println("-slow flag starts up using data in the Java heap");
    System.exit(0);
  }

  public VertexArrayRange() {
    setFlag(' ', true);   // animation on
    setFlag('i', true);   // infinite viewer and light
    setFlag('v', true);   // VAR on
  }

  //----------------------------------------------------------------------
  // Internals only below this point
  //

  private GLU glu = new GLU();
  private boolean[] b = new boolean[256];
  private static final int SIZEOF_FLOAT = 4;
  private static final int STRIP_SIZE  = 48;
  private int tileSize   = 9 * STRIP_SIZE;
  private int numBuffers = 4;
  private int bufferLength = 1000000;
  private int bufferSize   = bufferLength * SIZEOF_FLOAT;
  private static final int SIN_ARRAY_SIZE = 1024;

  private FloatBuffer bigArrayVar;
  private FloatBuffer bigArraySystem;
  private FloatBuffer bigArray;
  private IntBuffer[] elements;
  private float[]    xyArray;

  static class VarBuffer {
    public FloatBuffer vertices;
    public FloatBuffer normals;
    public int        fence;
  }
  private VarBuffer[] buffers;

  private float[] sinArray;
  private float[] cosArray;

  // Primitive: GL_QUAD_STRIP, GL_LINE_STRIP, or GL_POINTS
  private int primitive = GL2.GL_QUAD_STRIP;

  // Animation parameters
  private float hicoef = .06f;
  private float locoef = .10f;
  private float hifreq = 6.1f;
  private float lofreq = 2.5f;
  private float phaseRate = .02f;
  private float phase2Rate = -0.12f;
  private float phase  = 0;
  private float phase2 = 0;

  // Temporaries for computation
  float[] ysinlo = new float[STRIP_SIZE];
  float[] ycoslo = new float[STRIP_SIZE];
  float[] ysinhi = new float[STRIP_SIZE];
  float[] ycoshi = new float[STRIP_SIZE];

  // For thread-safety when dealing with keypresses
  private volatile boolean toggleVAR           = false;
  private volatile boolean toggleLighting      = false;
  private volatile boolean toggleLightingModel = false;
  private volatile boolean recomputeElements   = false;

  // Frames-per-second computation
  private boolean firstProfiledFrame;
  private int     profiledFrameCount;
  private int     numDrawElementsCalls;
  private long startTimeMillis;

  static class PeriodicIterator {
    public PeriodicIterator(int arraySize,
                            float period,
                            float initialOffset,
                            float delta) {
      float arrayDelta =  arraySize * (delta / period); // floating-point steps-per-increment
      increment = (int)(arrayDelta * (1<<16));          // fixed-point steps-per-increment

      float offset = arraySize * (initialOffset / period); // floating-point initial index
      initOffset = (int)(offset * (1<<16));                // fixed-point initial index

        arraySizeMask = 0;
        int i = 20; // array should be reasonably sized...
        while((arraySize & (1<<i)) == 0) {
          i--;
        }
        arraySizeMask = (1<<i)-1;
        index = initOffset;
    }

    public PeriodicIterator(PeriodicIterator arg) {
      this.arraySizeMask = arg.arraySizeMask;
      this.increment = arg.increment;
      this.initOffset = arg.initOffset;
      this.index = arg.index;
    }

    public int getIndex() {
      return (index >> 16) & arraySizeMask;
    }

    public void incr() {
      index += increment;
    }

    public void decr() {
      index -= increment;
    }

    public void reset() {
      index = initOffset;
    }

    private int arraySizeMask;
    // fraction bits == 16
    private int increment;
    private int initOffset;
    private int index;
  }

  private void setFlag(char key, boolean val) {
    b[((int) key) & 0xFF] = val;
  }

  private boolean getFlag(char key) {
    return b[((int) key) & 0xFF];
  }

  private void ensurePresent(GL gl, String function) {
    if (!gl.isFunctionAvailable(function)) {
      final String message = "OpenGL routine \"" + function + "\" not available";
      new Thread(new Runnable() {
          public void run() {
            JOptionPane.showMessageDialog(null, message, "Unavailable extension", JOptionPane.ERROR_MESSAGE);
            shutdownDemo();
          }
        }).start();
      throw new RuntimeException(message);
    }
  }

  public void init(GLAutoDrawable drawable) {
    //    drawable.setGL(new TraceGL(drawable.getGL(), System.err));
    //    drawable.setGL(new DebugGL(drawable.getGL()));

    GL2 gl = drawable.getGL().getGL2();

    // Try and disable synch-to-retrace for fastest framerate
    gl.setSwapInterval(0);

    try {
      ensurePresent(gl, "glVertexArrayRangeNV");
      ensurePresent(gl, "glGenFencesNV");
      ensurePresent(gl, "glSetFenceNV");
      ensurePresent(gl, "glTestFenceNV");
      ensurePresent(gl, "glFinishFenceNV");
      ensurePresent(gl, "glAllocateMemoryNV");
    } catch (RuntimeException e) {
      shutdownDemo();
      throw (e);
    }      
      
    gl.glEnable(GL.GL_DEPTH_TEST);

    gl.glClearColor(0, 0, 0, 0);

    gl.glEnable(GL2ES1.GL_LIGHT0);
    gl.glEnable(GL2ES1.GL_LIGHTING);
    gl.glEnable(GL2ES1.GL_NORMALIZE);
    gl.glMaterialfv(GL.GL_FRONT_AND_BACK, GL2ES1.GL_AMBIENT, new float[]  {.1f, .1f,    0, 1}, 0);
    gl.glMaterialfv(GL.GL_FRONT_AND_BACK, GL2ES1.GL_DIFFUSE, new float[]  {.6f, .6f,  .1f, 1}, 0);
    gl.glMaterialfv(GL.GL_FRONT_AND_BACK, GL2ES1.GL_SPECULAR, new float[] { 1,    1, .75f, 1}, 0);
    gl.glMaterialf(GL.GL_FRONT_AND_BACK, GL2ES1.GL_SHININESS, 128.f);

    gl.glLightfv(GL2ES1.GL_LIGHT0, GL2ES1.GL_POSITION, new float[] { .5f, 0, .5f, 0}, 0);
    gl.glLightModeli(GL2.GL_LIGHT_MODEL_LOCAL_VIEWER, 0);

    // NOTE: it looks like GLUT (or something else) sets up the
    // projection matrix in the C version of this demo.
    gl.glMatrixMode(GL2ES1.GL_PROJECTION);
    gl.glLoadIdentity();
    glu.gluPerspective(60, 1.0, 0.1, 100);
    gl.glMatrixMode(GL2ES1.GL_MODELVIEW);

    allocateBigArray(gl, true);
    allocateBuffersAndFences(gl);

    sinArray = new float[SIN_ARRAY_SIZE];
    cosArray = new float[SIN_ARRAY_SIZE];

    for (int i = 0; i < SIN_ARRAY_SIZE; i++) {
      double step = i * 2 * Math.PI / SIN_ARRAY_SIZE;
      sinArray[i] = (float) Math.sin(step);
      cosArray[i] = (float) Math.cos(step);
    }

    if (getFlag('v')) {
      gl.glEnableClientState(GL2.GL_VERTEX_ARRAY_RANGE_NV);
      gl.glVertexArrayRangeNV(bufferSize, bigArrayVar);
      bigArray = bigArrayVar;
    } else {
      bigArray = bigArraySystem;
    }
    setupBuffers();
    gl.glEnableClientState(GL2ES1.GL_VERTEX_ARRAY);
    gl.glEnableClientState(GL2ES1.GL_NORMAL_ARRAY);

    computeElements();
  }

  private void allocateBuffersAndFences(GL2 gl) {
    buffers = new VarBuffer[numBuffers];
    int[] fences = new int[1];
    for (int i = 0; i < numBuffers; i++) {
      buffers[i] = new VarBuffer();
      gl.glGenFencesNV(1, fences, 0);
      buffers[i].fence = fences[0];
    }
  }

  private void setupBuffers() {
    int sliceSize = bufferLength / numBuffers;
    for (int i = 0; i < numBuffers; i++) {
      int startIndex = i * sliceSize;
      buffers[i].vertices = sliceBuffer(bigArray, startIndex, sliceSize);
      buffers[i].normals  = sliceBuffer(buffers[i].vertices, 3,
                                        buffers[i].vertices.limit() - 3);
    }
  }

  private void dispatchKey(char k) {
    setFlag(k, !getFlag(k));
    // Quit on escape or 'q'
    if ((k == (char) 27) || (k == 'q')) {
      shutdownDemo();
      return;
    }

    if (k == 'r') {
      if (getFlag(k)) {
        profiledFrameCount = 0;
        numDrawElementsCalls = 0;
        firstProfiledFrame = true;
      }
    }

    if (k == 'w') {
      if (getFlag(k)) {
        primitive = GL2.GL_LINE_STRIP;
      } else {
        primitive = GL2.GL_QUAD_STRIP;
      }
    }

    if (k == 'p') {
      if (getFlag(k)) {
        primitive = GL2.GL_POINTS;
      } else {
        primitive = GL2.GL_QUAD_STRIP;
      }
    }

    if (k == 'v') {
      toggleVAR = true;
    }

    if (k == 'd') {
      toggleLighting = true;
    }

    if (k == 'i') {
      toggleLightingModel = true;
    }

    if('h'==k)
      hicoef += .005;
    if('H'==k)
      hicoef -= .005;
    if('l'==k)
      locoef += .005;
    if('L'==k)
      locoef -= .005;
    if('1'==k)
      lofreq += .1f;
    if('2'==k)
      lofreq -= .1f;
    if('3'==k)
      hifreq += .1f;
    if('4'==k)
      hifreq -= .1f;
    if('5'==k)
      phaseRate += .01f;
    if('6'==k)
      phaseRate -= .01f;
    if('7'==k)
      phase2Rate += .01f;
    if('8'==k)
      phase2Rate -= .01f;

    if('t'==k) {
      if(tileSize < 864) {
        tileSize += STRIP_SIZE;
        recomputeElements = true;
        System.err.println("tileSize = " + tileSize);
      }
    }

    if('T'==k) {
      if(tileSize > STRIP_SIZE) {
        tileSize -= STRIP_SIZE;
        recomputeElements = true;
        System.err.println("tileSize = " + tileSize);
      }
    }
  }

  public void dispose(GLAutoDrawable drawable) {
  }

  public void display(GLAutoDrawable drawable) {
    GL2 gl = drawable.getGL().getGL2();

    // Check to see whether to animate
    if (getFlag(' ')) {
      phase += phaseRate;
      phase2 += phase2Rate;

      if (phase > (float) (20 * Math.PI)) {
        phase = 0;
      }

      if (phase2 < (float) (-20 * Math.PI)) {
        phase2 = 0;
      }
    }

    PeriodicIterator loX =
      new PeriodicIterator(SIN_ARRAY_SIZE, (float) (2 * Math.PI), phase, (float) ((1.f/tileSize)*lofreq*Math.PI));
    PeriodicIterator loY = new PeriodicIterator(loX);
    PeriodicIterator hiX =
      new PeriodicIterator(SIN_ARRAY_SIZE, (float) (2 * Math.PI), phase2, (float) ((1.f/tileSize)*hifreq*Math.PI));
    PeriodicIterator hiY = new PeriodicIterator(hiX);

    if (toggleVAR) {
      if (getFlag('v')) {
        gl.glEnableClientState(GL2.GL_VERTEX_ARRAY_RANGE_NV);
        gl.glVertexArrayRangeNV(bufferSize, bigArrayVar);
        bigArray = bigArrayVar;
      } else {
        gl.glDisableClientState(GL2.GL_VERTEX_ARRAY_RANGE_NV);
        bigArray = bigArraySystem;
      }
      toggleVAR = false;
      setupBuffers();
    }

    if (toggleLighting) {
      if (getFlag('d')) {
        gl.glDisable(GL2ES1.GL_LIGHTING);
      } else {
        gl.glEnable(GL2ES1.GL_LIGHTING);
      }
      toggleLighting = false;
    }

    if (toggleLightingModel) {
      if(getFlag('i')) {
        // infinite light
        gl.glLightfv(GL2ES1.GL_LIGHT0, GL2ES1.GL_POSITION, new float[] { .5f, 0, .5f, 0 }, 0);
        gl.glLightModeli(GL2.GL_LIGHT_MODEL_LOCAL_VIEWER, 0);
      } else {
        gl.glLightfv(GL2ES1.GL_LIGHT0, GL2ES1.GL_POSITION, new float[] { .5f, 0, -.5f, 1 }, 0);
        gl.glLightModeli(GL2.GL_LIGHT_MODEL_LOCAL_VIEWER, 1);
      }
      toggleLightingModel = false;
    }

    if (recomputeElements) {
      computeElements();
      recomputeElements = false;
    }

    gl.glClear(GL.GL_COLOR_BUFFER_BIT | GL.GL_DEPTH_BUFFER_BIT);

    gl.glPushMatrix();

    final float[] modelViewMatrix = new float[] {
      1, 0, 0, 0,
      0, 1, 0, 0,
      0, 0, 1, 0,
      0, 0, -1, 1
    };
    gl.glLoadMatrixf(modelViewMatrix, 0);

    // FIXME: add mouse interaction
    // camera.apply_inverse_transform();
    // object.apply_transform();

    int cur = 0;
    int numSlabs = tileSize / STRIP_SIZE;

    for(int slab = numSlabs; --slab>=0; ) {
      cur = slab % numBuffers;
      if (slab >= numBuffers) {
        if (!gl.glTestFenceNV(buffers[cur].fence)) {
          gl.glFinishFenceNV(buffers[cur].fence);
        }
      }

      FloatBuffer v = buffers[cur].vertices;
      int vertexIndex = 0;

      gl.glVertexPointer(3, GL.GL_FLOAT, 6 * SIZEOF_FLOAT, v);
      gl.glNormalPointer(GL.GL_FLOAT, 6 * SIZEOF_FLOAT, buffers[cur].normals);

      for(int jj=STRIP_SIZE; --jj>=0; ) {
        ysinlo[jj] = sinArray[loY.getIndex()];
        ycoslo[jj] = cosArray[loY.getIndex()]; loY.incr();
        ysinhi[jj] = sinArray[hiY.getIndex()];
        ycoshi[jj] = cosArray[hiY.getIndex()]; hiY.incr();
      }
      loY.decr();
      hiY.decr();

      for(int i = tileSize; --i>=0; ) {
        float x = xyArray[i];
        int loXIndex = loX.getIndex();
        int hiXIndex = hiX.getIndex();

        int jOffset = (STRIP_SIZE-1)*slab;
        float nx = locoef * -cosArray[loXIndex] + hicoef * -cosArray[hiXIndex];

        // Help the HotSpot Client Compiler by hoisting loop
        // invariant variables into locals. Note that this may be
        // good practice for innermost loops anyway since under
        // the new memory model operations like accidental
        // synchronization may force any compiler to reload these
        // fields from memory, destroying their ability to
        // optimize.
        float locoef_tmp = locoef;
        float hicoef_tmp = hicoef;
        float[] ysinlo_tmp = ysinlo;
        float[] ysinhi_tmp = ysinhi;
        float[] ycoslo_tmp = ycoslo;
        float[] ycoshi_tmp = ycoshi;
        float[] sinArray_tmp = sinArray;
        float[] xyArray_tmp = xyArray;

        for(int j = STRIP_SIZE; --j>=0; ) {
          float y;

          y = xyArray_tmp[j + jOffset];

          float ny;

          v.put(vertexIndex, x);
          v.put(vertexIndex + 1, y);
          v.put(vertexIndex + 2, (locoef_tmp * (sinArray_tmp[loXIndex] + ysinlo_tmp[j]) +
                                  hicoef_tmp * (sinArray_tmp[hiXIndex] + ysinhi_tmp[j])));
          v.put(vertexIndex + 3, nx);
          ny = locoef_tmp * -ycoslo_tmp[j] + hicoef_tmp * -ycoshi_tmp[j];
          v.put(vertexIndex + 4, ny);
          v.put(vertexIndex + 5, .15f); //.15f * (1.f - sqrt(nx * nx + ny * ny));
          vertexIndex += 6;
        }
        loX.incr();
        hiX.incr();
      }
      loX.reset();
      hiX.reset();

      for (int i = 0; i < elements.length; i++) {
        ++numDrawElementsCalls;
        gl.glDrawElements(primitive, elements[i].capacity(), GL2.GL_UNSIGNED_INT, elements[i]);
        if(getFlag('f')) {
          gl.glFlush();
        }
      }

      gl.glSetFenceNV(buffers[cur].fence, GL2.GL_ALL_COMPLETED_NV);
    }

    gl.glPopMatrix();

    gl.glFinishFenceNV(buffers[cur].fence);

    if (getFlag('r')) {
      if (!firstProfiledFrame) {
        if (++profiledFrameCount == 30) {
          long endTimeMillis = System.currentTimeMillis();
          double secs = (endTimeMillis - startTimeMillis) / 1000.0;
          double fps  = 30.0 / secs;
          double ppf  = tileSize * tileSize * 2;
          double mpps = ppf * fps / 1000000.0;
          System.err.println("fps: " + fps + " polys/frame: " + ppf + " million polys/sec: " + mpps +
                             " DrawElements calls/frame: " + (numDrawElementsCalls / 30));
          profiledFrameCount = 0;
          numDrawElementsCalls = 0;
          startTimeMillis = System.currentTimeMillis();
        }
      } else {
        startTimeMillis = System.currentTimeMillis();
        firstProfiledFrame = false;

      }
    }
  }

  public void reshape(GLAutoDrawable drawable, int x, int y, int width, int height) {}

  // Unused routines
  public void displayChanged(GLAutoDrawable drawable, boolean modeChanged, boolean deviceChanged) {}

  private void allocateBigArray(GL2 gl, boolean tryAgain) {
    float priority = .5f;

    bigArraySystem = setupBuffer(ByteBuffer.allocateDirect(bufferSize));

    float megabytes = (bufferSize / 1000000.f);
    try {
      bigArrayVar = setupBuffer(gl.glAllocateMemoryNV(bufferSize, 0, 0, priority));
    }
    catch (OutOfMemoryError e1) {
      // Try a higher priority
      try {
        bigArrayVar = setupBuffer(gl.glAllocateMemoryNV(bufferSize, 0, 0, 1.f));
      }
      catch (OutOfMemoryError e2) {
        if (!tryAgain) {
          throw new RuntimeException("Unable to allocate " + megabytes +
                                     " megabytes of fast memory. Giving up.");
        }

        System.err.println("Unable to allocate " + megabytes +
                           " megabytes of fast memory. Trying less.");
        bufferSize /= 2;
        numBuffers /= 2;
        allocateBigArray(gl, false);
        return;
      }
    }

    System.err.println("Allocated " + megabytes + " megabytes of fast memory");
  }

  private FloatBuffer setupBuffer(ByteBuffer buf) {
    buf.order(ByteOrder.nativeOrder());
    return buf.asFloatBuffer();
  }

  private FloatBuffer sliceBuffer(FloatBuffer array,
                                  int sliceStartIndex, int sliceLength) {
    array.position(sliceStartIndex);
    FloatBuffer ret = array.slice();
    array.position(0);
    ret.limit(sliceLength);
    return ret;
  }

  private void computeElements() {
    xyArray = new float[tileSize];
    for (int i = 0; i < tileSize; i++) {
      xyArray[i] = i / (tileSize - 1.0f) - 0.5f;
    }

    elements = new IntBuffer[tileSize - 1];
    for (int i = 0; i < tileSize - 1; i++) {
      elements[i] = IntBuffer.allocate(2 * STRIP_SIZE);
      for (int j = 0; j < 2 * STRIP_SIZE; j += 2) {
        elements[i].put(j,    i      * STRIP_SIZE + (j / 2));
        elements[i].put(j+1, (i + 1) * STRIP_SIZE + (j / 2));
      }
    }
  }

  private static void runExit(final Animator animator) {
    // Note: calling System.exit() synchronously inside the draw,
    // reshape or init callbacks can lead to deadlocks on certain
    // platforms (in particular, X11) because the JAWT's locking
    // routines cause a global AWT lock to be grabbed. Run the
    // exit routine in another thread.
    new Thread(new Runnable() {
        public void run() {
          animator.stop();
          System.exit(0);
        }
      }).start();
  }
}