Polygon.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.math;

public class Polygon {
	private final float[] localVertices;
	private float[] worldVertices;
	private float x, y;
	private float originX, originY;
	private float rotation;
	private float scaleX = 1, scaleY = 1;
	private boolean dirty = true;
	private Rectangle bounds;

	public Polygon(float[] vertices) {
		if (vertices.length < 6)
			throw new IllegalArgumentException("polygons must contain at least 3 points.");
		this.localVertices = vertices;
	}

	/** Returns vertices without scaling or rotation and without being offset by the polygon position. */
	public float[] getVertices() {
		return localVertices;
	}

	/** Returns vertices scaled, rotated, and offset by the polygon position. */
	public float[] getTransformedVertices() {
		if (!dirty)
			return worldVertices;
		dirty = false;

		final float[] localVertices = this.localVertices;
		if (worldVertices == null || worldVertices.length < localVertices.length)
			worldVertices = new float[localVertices.length];

		final float[] worldVertices = this.worldVertices;
		final float positionX = x;
		final float positionY = y;
		final float originX = this.originX;
		final float originY = this.originY;
		final float scaleX = this.scaleX;
		final float scaleY = this.scaleY;
		final boolean scale = scaleX != 1 || scaleY != 1;
		final float rotation = this.rotation;
		final float cos = MathUtils.cosDeg(rotation);
		final float sin = MathUtils.sinDeg(rotation);

		for (int i = 0, n = localVertices.length; i < n; i += 2) {
			float x = localVertices[i] - originX;
			float y = localVertices[i + 1] - originY;

			// scale if needed
			if (scale) {
				x *= scaleX;
				y *= scaleY;
			}

			// rotate if needed
			if (rotation != 0) {
				float oldX = x;
				x = cos * x - sin * y;
				y = sin * oldX + cos * y;
			}

			worldVertices[i] = positionX + x + originX;
			worldVertices[i + 1] = positionY + y + originY;
		}
		return worldVertices;
	}

	public void setOrigin(float originX, float originY) {
		this.originX = originX;
		this.originY = originY;
		dirty = true;
	}

	public void setPosition(float x, float y) {
		this.x = x;
		this.y = y;
		dirty = true;
	}

	public void translate(float x, float y) {
		this.x += x;
		this.y += y;
		dirty = true;
	}

	public void setRotation(float degrees) {
		this.rotation = degrees;
		dirty = true;
	}

	public void rotate(float degrees) {
		rotation += degrees;
		dirty = true;
	}

	public void setScale(float scaleX, float scaleY) {
		this.scaleX = scaleX;
		this.scaleY = scaleY;
		dirty = true;
	}

	public void scale(float amount) {
		this.scaleX += amount;
		this.scaleY += amount;
		dirty = true;
	}

	public void dirty() {
		dirty = true;
	}

	public float area() {
		float area = 0;

		float[] vertices = getTransformedVertices();
		final int numFloats = vertices.length;

		int x1, y1, x2, y2;
		for (int i = 0; i < numFloats; i += 2) {
			x1 = i;
			y1 = i + 1;
			x2 = (i + 2) % numFloats;
			y2 = (i + 3) % numFloats;

			area += vertices[x1] * vertices[y2];
			area -= vertices[x2] * vertices[y1];
		}
		area *= 0.5f;
		return area;
	}

	public Rectangle getBoundingRectangle() {
		float[] vertices = getTransformedVertices();

		float minX = vertices[0];
		float minY = vertices[1];
		float maxX = vertices[0];
		float maxY = vertices[1];

		final int numFloats = vertices.length;
		for (int i = 2; i < numFloats; i += 2) {
			minX = minX > vertices[i] ? vertices[i] : minX;
			minY = minY > vertices[i + 1] ? vertices[i + 1] : minY;
			maxX = maxX < vertices[i] ? vertices[i] : maxX;
			maxY = maxY < vertices[i + 1] ? vertices[i + 1] : maxY;
		}

		if (bounds == null)
			bounds = new Rectangle();
		bounds.x = minX;
		bounds.y = minY;
		bounds.width = maxX - minX;
		bounds.height = maxY - minY;

		return bounds;
	}

	public boolean contains(float x, float y) {
		final float[] vertices = getTransformedVertices();
		final int numFloats = vertices.length;
		int intersects = 0;

		for (int i = 0; i < numFloats; i += 2) {
			float x1 = vertices[i];
			float y1 = vertices[i + 1];
			float x2 = vertices[(i + 2) % numFloats];
			float y2 = vertices[(i + 3) % numFloats];
			if (((y1 <= y && y < y2) || (y2 <= y && y < y1)) && x < ((x2 - x1) / (y2 - y1) * (y - y1) + x1))
				intersects++;
		}
		return (intersects & 1) == 1;
	}

	public float getX() {
		return x;
	}

	public float getY() {
		return y;
	}

	public float getOriginX() {
		return originX;
	}

	public float getOriginY() {
		return originY;
	}

	public float getRotation() {
		return rotation;
	}

	public float getScaleX() {
		return scaleX;
	}

	public float getScaleY() {
		return scaleY;
	}
}