Android Open Source - 4est Vindexer

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License

The source code is released under:
MIT License
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Java Source Code

package com.wordsaretoys.rise.meshutil;
//from  ww w  .j av  a2 s. c  om
import android.util.Log;

/**
 * Index generator for 3D vertexes
 * 
 * implements an octree in a fixed-size array;
 * as the mesh object only allows short ints
 * to be used for indexes, we don't bother to
 * make the array length > 64k
 * 
 * @author chris
 *
 */

public class Vindexer {

  static public final int INDEX_MASK = 0xFFFF;
  static public final int ADD_VERTEX= 0xFFFF0000;
  
  static private final int MAX_INDEX = 65536;
  static private final float MIN_LIMIT = 0.0001f;

  private float[] vertex;
  private int[] child;

  private int length;
  
  private int hits;
  
  /**
   * constructor, generates fixed array
   */
  public Vindexer() {
    vertex = new float[3 * MAX_INDEX];
    child = new int[8 * MAX_INDEX];
    reset();
  }
  
  /**
   * call prior to generating new indexes
   */
  public void reset() {
    length = 0;
    hits = 0;
  }
  
  /**
   * check that a specific vertex is in the octree,
   * create it if it isn't. either way, return the
   * index of the vertex.
   * 
   * if the indexer hasn't seen this vertex yet, I
   * assume the calling code needs to add it to a
   * vertex buffer, so the ADD_VERTEX flag is ORed
   * with the index. typically, you'd do something
   * like this:
   * 
   *     int result = vindexer.check(x, y, z);
   *     int index = result & Vindexer.ADD_VERTEX
   *     if (index != result) {
   *       // add vertex to buffer
   *       vertexbuffer.set(x, y, z);
   *     }
   *     indexbuffer.set(index);
   * 
   * 
   * @param x, y, z coordinates of vertex
   * @return index of new or stored vertex, maybe ORed with 
   * ADD_VERTEX if new vertex (see above)
   */
  public int check(float x, float y, float z) {
    int vin, cin, index = 0;
    
    while (index < length) {
      
      vin = index * 3;
      cin = index * 8;
      
      float vx = vertex[vin];
      float vy = vertex[vin + 1];
      float vz = vertex[vin + 2];
      
      // if this entry matches our vertex
      if ( (Math.abs(x - vx) < MIN_LIMIT) && (Math.abs(y - vy) < MIN_LIMIT) && (Math.abs(z - vz) < MIN_LIMIT)) {
        // our search is over
        hits++;
        return index;
      }
      
      // traverse to the next child, if available
      int ch = cin + ((x > vx) ? 4 : 0) + ((y > vy) ? 2 : 0) + ((z > vz) ? 1 : 0);
      if (child[ch] != -1) {
        index = child[ch];
      } else {
        child[ch] = (int)length;
        index = length;
      }
      
    }

    // no entries found, create one
    vin = length * 3;
    cin = length * 8;

    vertex[vin] = x;
    vertex[vin + 1] = y;
    vertex[vin + 2] = z;

    for (int i = 0; i < 8; i++) {
      child[cin + i] = -1;
    }
    
    index = length++;
    
    // this should never happen, obviously
    if (length >= MAX_INDEX) {
      throw new RuntimeException("Vindexer exceeded index limits");
    }
    
    // return index with "add vertex" flag in upper word
    return index | ADD_VERTEX;
  }
  
  public void report() {
    int hpi = hits / length;
    Log.i("4est", "vindexer generated " + length + " indexes, with " + hits + " hits (" + hpi + " hits/index)");
  }
  
}
Java Source Code List
