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simple utility methods to make life with OpenGL core profile simpler
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/**
 * Copyright (c) 2013, Jens Hohmuth
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *  * Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *  * Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
 * THE POSSIBILITY OF SUCH DAMAGE.
 */
package de.lessvoid.math;

/**
 * Creates Mat4 instances for projection- and ortho projection.
 * 
 * @author void
 */
public class MatrixFactory {

  /**
   * Create orthographic projection Matrix4f.
   * 
   * @return new Matrix4j
   */
  public static Mat4 createOrtho(final float left, final float right, final float bottom, final float top) {
    final float zNear = -9999;
    final float zFar = 9999;

    final Mat4 projection = new Mat4();
    projection.m00 = 2 / (right - left);
    projection.m11 = 2 / (top - bottom);
    projection.m22 = -2 / (zFar - zNear);
    projection.m30 = -(right + left) / (right - left);
    projection.m31 = -(top + bottom) / (top - bottom);
    projection.m32 = -(zFar + zNear) / (zFar - zNear);
    projection.m33 = 1;
    return projection;
  }

  /**
   * Create perspective projection Matrix4f in glFrustrum() style =)
   *
   * @param left
   *          left
   * @param right
   *          right
   * @param top
   *          top
   * @param bottom
   *          bottom
   * @param zNear
   *          z near value (for example 1)
   * @param zFar
   *          z far value (for example 10000)
   * @return new perspective projection matrix
   */
  public static Mat4 createProjection(final float left,
                                      final float right,
                                      final float top,
                                      final float bottom,
                                      final float zNear,
                                      final float zFar) {
    final Mat4 projection = new Mat4();
    projection.m00 = 2.f * zNear / (right - left);
    projection.m11 = 2.f * zNear / (top - bottom);
    projection.m20 = (right + left) / (right - left);
    projection.m21 = (top + bottom) / (top - bottom);
    projection.m22 = -(zFar + zNear) / (zFar - zNear);
    projection.m23 = -1.f;
    projection.m32 = -2.f * zFar * zNear / (zFar - zNear);
    projection.m33 = 0.f;
    return projection;
  }

  /**
   * Create perspective projection Matrix4f with fov
   * 
   * @param fov
   * @param aspectRatio
   * @param zNear
   * @param zFar
   * @return
   */
  public static Mat4 createProjection(final float fov, final float aspectRatio, final float zNear, final float zFar) {
    final Mat4 projection = new Mat4();
    final float e = 1.f / (float) Math.tan(fov / 2.f);
    projection.m00 = e;
    projection.m11 = e / aspectRatio;
    projection.m22 = -(zFar + zNear) / (zFar - zNear);
    projection.m23 = -1.f;
    projection.m32 = -2.f * zFar * zNear / (zFar - zNear);
    projection.m33 = 0.f;
    return projection;
  }

  public static Mat4 createProjection2(final float fov, final float aspectRatio, final float zNear, final float zFar) {
    final float DEG2RAD = (float) (Math.PI / 180.f);

    final float tangent = (float) Math.tan(fov / 2 * DEG2RAD); // tangent of
                                                               // half fovY
    final float height = zNear * tangent; // half height of near plane
    final float width = height * aspectRatio; // half width of near plane

    // params: left, right, bottom, top, near, far
    return createProjection2(-width, width, -height, height, zNear, zFar);
  }

  public static Mat4 createProjection2(final float left,
                                       final float right,
                                       final float bottom,
                                       final float top,
                                       final float near,
                                       final float far) {
    final float A = -(right + left) / (right - left);
    final float B = -(top + bottom) / (top - bottom);
    final float C = -(far + near) / (far - near);
    final float D = -2 * far * near / (far - near);

    final Mat4 projection = new Mat4();
    projection.m00 = 2.f / (right - left);
    projection.m20 = A;
    projection.m11 = 2.f / (top - bottom);
    projection.m21 = B;
    projection.m22 = C;
    projection.m32 = D;
    projection.m23 = -1.f;
    projection.m33 = 0.f;
    return projection;
  }

}