PPolygon.java

/**
 * Copyright 2013 The Loon Authors
 *
 * 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 loon.physics;

import loon.geom.Vector2f;

public class PPolygon {

	int numVertices;
	boolean polygonized;
	float[] xs;
	float[] ys;

	public PPolygon(float[] xs, float[] ys) {
		this.numVertices = xs.length;
		this.xs = xs;
		this.ys = ys;
	}

	public PPolygon(float[] points) {
		this(points, 1f);
	}

	public PPolygon(float[] points, float scale) {
		this.numVertices = points.length;
		int half = numVertices / 2;
		this.xs = new float[half];
		this.ys = new float[half];
		for (int i = 0, j = 0; i < numVertices; i += 2, j++) {
			this.xs[j] = points[i] / scale;
			this.ys[j] = points[i + 1] / scale;
		}
	}

	public PPolygon(Vector2f[] vertices) {
		numVertices = vertices.length;
		xs = new float[numVertices];
		ys = new float[numVertices];
		for (int i = 0; i < numVertices; i++) {
			xs[i] = vertices[i].x;
			ys[i] = vertices[i].y;
		}
	}

	public boolean isClockwise() {
		float area = 0.0F;
		for (int i = 0; i < numVertices; i++) {
			int next = (i + 1) % numVertices;
			float x1 = xs[i];
			float y1 = ys[i];
			float x2 = xs[next];
			float y2 = ys[next];
			area += x1 * y2 - y1 * x2;
		}
		return area > 0.0F;
	}

	public boolean isConvex() {
		int cross = 0;
		for (int i = 0; i < numVertices; i++) {
			int prev = ((i + numVertices) - 1) % numVertices;
			int next = (i + 1) % numVertices;
			int c = (xs[i] - xs[prev]) * (ys[next] - ys[i])
					- (xs[next] - xs[i]) * (ys[i] - ys[prev]) <= 0.0F ? -1 : 1;
			if (cross == 0) {
				cross = c;
			} else {
				if (cross != c) {
					return false;
				}
			}
		}
		return true;
	}
}