Transform.java

/*******************************************************************************
 * Copyright 2011 See AUTHORS file.
 * 
 * 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.badlogic.gdx.physics.box2d;

import com.badlogic.gdx.math.Vector2;

/**
 * Encodes a Box2D transform. We are lazy so we only store a 4 float wide array. First two floats are the position of
 * the b2Transform struct. Next two floats are the cosine and sine of the rotation angle.
 * 
 * @author mzechner
 */
public class Transform {
	public static final int POS_X = 0;
	public static final int POS_Y = 1;
	public static final int COS = 2;
	public static final int SIN = 3;

	public float[] vals = new float[4];

	private Vector2 position = new Vector2();

	public Transform() {

	}

	/**
	 * Constructs a new Transform instance with the given position and angle
	 * 
	 * @param position
	 *            the position
	 * @param angle
	 *            the angle in radians
	 */
	public Transform(Vector2 position, float angle) {
		setPosition(position);
		setRotation(angle);
	}

	/**
	 * Transforms the given vector by this transform
	 * 
	 * @param v
	 *            the vector
	 */
	public Vector2 mul(Vector2 v) {
		float x = vals[POS_X] + vals[COS] * v.x + -vals[SIN] * v.y;
		float y = vals[POS_Y] + vals[SIN] * v.x + vals[COS] * v.y;

		v.x = x;
		v.y = y;
		return v;
	}

	/** @return the position, modification of the vector has no effect on the Transform */
	public Vector2 getPosition() {
		return position.set(vals[0], vals[1]);
	}

	/**
	 * Sets the rotation of this transform
	 * 
	 * @param angle
	 *            angle in radians
	 */
	public void setRotation(float angle) {
		float c = (float) Math.cos(angle), s = (float) Math.sin(angle);
		vals[COS] = c;
		vals[SIN] = s;
	}

	public float getRotation() {
		return (float) Math.atan2(vals[SIN], vals[COS]);
	}

	/**
	 * Sets the position of this transform
	 * 
	 * @param pos
	 *            the position
	 */
	public void setPosition(Vector2 pos) {
		this.vals[POS_X] = pos.x;
		this.vals[POS_Y] = pos.y;
	}
}