Matrix33.java

// Copyright 2008 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package com.google.android.stardroid.units;

/**
 * Class for representing a 3x3 matrix explicitly, avoiding heap
 * allocation as far as possible.
 *
 * @author Dominic Widdows
 */
public class Matrix33 implements Cloneable {

  public float xx;
  public float xy;
  public float xz;
  public float yx;
  public float yy;
  public float yz;
  public float zx;
  public float zy;
  public float zz;

  /**
   * Construct a new matrix.
   * @param xx row 1, col 1
   * @param xy row 1, col 2
   * @param xz row 1, col 3
   * @param yx row 2, col 1
   * @param yy row 2, col 2
   * @param yz row 2, col 3
   * @param zx row 3, col 1
   * @param zy row 3, col 2
   * @param zz row 3, col 3
   */
  public Matrix33(float xx, float xy, float xz,
                  float yx, float yy, float yz,
                  float zx, float zy, float zz) {
    this.xx = xx;
    this.xy = xy;
    this.xz = xz;
    this.yx = yx;
    this.yy = yy;
    this.yz = yz;
    this.zx = zx;
    this.zy = zy;
    this.zz = zz;
  }

  /**
   * Construct a matrix from three column vectors.
   */
  public Matrix33(Vector3 v1, Vector3 v2, Vector3 v3) {
    this(v1, v2, v3, true);
  }

  /**
   * Construct a matrix from three vectors.
   * @param columnVectors true if the vectors are column vectors, otherwise
   * they're row vectors.
   */
  public Matrix33(Vector3 v1, Vector3 v2, Vector3 v3, boolean columnVectors) {
    if (columnVectors) {
      this.xx = v1.x;
      this.yx = v1.y;
      this.zx = v1.z;
      this.xy = v2.x;
      this.yy = v2.y;
      this.zy = v2.z;
      this.xz = v3.x;
      this.yz = v3.y;
      this.zz = v3.z;
    } else {
      this.xx = v1.x;
      this.xy = v1.y;
      this.xz = v1.z;
      this.yx = v2.x;
      this.yy = v2.y;
      this.yz = v2.z;
      this.zx = v3.x;
      this.zy = v3.y;
      this.zz = v3.z;
    }
  }

  // TODO(widdows): rename this to something like copyOf().
  @Override
  public Matrix33 clone() {
    return new Matrix33(xx, xy, xz,
                        yx, yy, yz,
                        zx, zy, zz);
  }

  public static Matrix33 getIdMatrix() {
    return new Matrix33(1, 0, 0, 0, 1, 0, 0, 0, 1);
  }

  /**
   * Create a zero matrix.
   */
  public Matrix33() {
    new Matrix33(0, 0, 0, 0, 0, 0, 0, 0, 0);
  }

  public float getDeterminant() {
    return xx*yy*zz + xy*yz*zx + xz*yx*zy - xx*yz*zy - yy*zx*xz - zz*xy*yx;
  }

  public Matrix33 getInverse() {
    float det = getDeterminant();
    if (det == 0.0) return null;
    return new Matrix33(
        (yy*zz - yz*zy) / det, (xz*zy - xy*zz) / det, (xy*yz - xz*yy) / det,
        (yz*zx - yx*zz) / det, (xx*zz - xz*zx) / det, (xz*yx - xx*yz) / det,
        (yx*zy - yy*zx) / det, (xy*zx - xx*zy) / det, (xx*yy - xy*yx) / det);
  }

  /**
   * Transpose the matrix, in place.
   */
  public void transpose() {
    float tmp;
    tmp = xy;
    xy = yx;
    yx = tmp;

    tmp = xz;
    xz = zx;
    zx = tmp;

    tmp = yz;
    yz = zy;
    zy = tmp;
  }
}