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BoofCV is an open source Java library for real-time computer vision and robotics applications.
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/*
 * Copyright (c) 2020, Peter Abeles. All Rights Reserved.
 *
 * This file is part of BoofCV (http://boofcv.org).
 *
 * 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 boofcv.misc;

import georegression.struct.point.Point2D_I32;
import org.ddogleg.struct.DogArray;

/**
 * Functions related to discretized circles for image processing
 *
 * @author Peter Abeles
 */
public class DiscretizedCircle {

	/**
	 * Computes the offsets for a discretized circle of the specified radius for an
	 * image with the specified width.
	 *
	 * @param radius   The radius of the circle in pixels.
	 * @param imgWidth The row step of the image
	 * @return A list of offsets that describe the circle
	 */
	public static int[] imageOffsets(double radius, int imgWidth) {


		double PI2 = Math.PI * 2.0;

		double circumference = PI2 * radius;
		int num = (int) Math.ceil(circumference);
		num = num - num % 4;

		double angleStep = PI2 / num;


		int temp[] = new int[(int) Math.ceil(circumference)];
		int i = 0;

		int prev = 0;

		for (double ang = 0; ang < PI2; ang += angleStep) {
			int x = (int) Math.round(Math.cos(ang) * radius);
			int y = (int) Math.round(Math.sin(ang) * radius);

			int pixel = y * imgWidth + x;

			if (pixel != prev) {
//                System.out.println("i = "+i+"  x = "+x+"  y = "+y);
				temp[i++] = pixel;
			}
			prev = pixel;
		}

		if (i == temp.length)
			return temp;
		else {
			int ret[] = new int[i];
			System.arraycopy(temp, 0, ret, 0, i);

			return ret;
		}
	}

	public static void coordinates(double radius, DogArray coordinates ) {

		coordinates.reset();

		double PI2 = Math.PI * 2.0;

		double circumference = PI2 * radius;
		int num = (int) Math.ceil(circumference);
		num = num - num % 4;

		double angleStep = PI2 / num;

		int width = (int)Math.ceil(radius)*2+1;

		int prev = 0;

		for (double ang = 0; ang < PI2; ang += angleStep) {
			int x = (int) Math.round(Math.cos(ang) * radius);
			int y = (int) Math.round(Math.sin(ang) * radius);


			int pixel = y * width + x;

			if (pixel != prev) {
				coordinates.grow().setTo(x,y);
			}
			prev = pixel;
		}
	}

	public static int[][] imageOffsets2(double radius) {


		double PI2 = Math.PI * 2.0;

		double circumference = PI2 * radius;
		int num = (int) Math.ceil(circumference);
		num = num - num % 4;

		double angleStep = PI2 / num;


		int temp[][] = new int[num][2];

		for (int i = 0; i < num; i++) {
			double ang = angleStep * i;
			int x = (int) Math.round(Math.cos(ang) * radius);
			int y = (int) Math.round(Math.sin(ang) * radius);

			temp[i][0] = x;
			temp[i][1] = y;


//            System.out.println("i = "+i+"  x = "+x+"  y = "+y);
		}

		return temp;
	}
}