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BoofCV is an open source Java library for real-time computer vision and robotics applications.
There is a newer version: 1.1.7
/*
 * Copyright (c) 2011-2020, 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.alg.feature.detect.extract;

import boofcv.concurrency.BoofConcurrency;
import boofcv.struct.QueueCorner;
import boofcv.struct.image.GrayF32;
import org.ddogleg.struct.FastQueue;

import javax.annotation.Nullable;

/**
 * Concurrent implementation of {@link NonMaxBlock_MT}. Every row of block is run in its own threads.
 * All threads keep track of all the found mins/maxs in seperate lists which are then combined after
 * a thread has finished running. All searches and point lists declared for each thread
 * are saved for future use
 *
 * @author Peter Abeles
 */
public class NonMaxBlock_MT extends NonMaxBlock {

	// lock for variables below - which are lists used to store work space for individual threads
	final FastQueue searches = new FastQueue<>(this::createSearchData);

	public NonMaxBlock_MT(Search search) {
		super(search);
	}

	/**
	 * Detects local minimums and/or maximums in the provided intensity image.
	 *
	 * @param intensityImage (Input) Feature intensity image.
	 * @param localMin (Output) storage for found local minimums.
	 * @param localMax (Output) storage for found local maximums.
	 */
	@Override
	public void process(GrayF32 intensityImage, @Nullable QueueCorner localMin, @Nullable QueueCorner localMax) {

		if( localMin != null )
			localMin.reset();
		if( localMax != null )
			localMax.reset();

		// the defines the region that can be processed
		int endX = intensityImage.width - border;
		int endY = intensityImage.height - border;

		int step = configuration.radius+1;

		search.initialize(configuration,intensityImage,localMin,localMax);

		// Compute number of y iterations
		int range = endY-border;
		int N = range/step;
		if( range > N*step )
			N += 1;

		// The previous version required locks. In a benchmark in Java 11 this lock free version and the previous
		// had identical performance.
		BoofConcurrency.loopBlocks(0,N,searches, (blockInfo,iter0,iter1) -> {
			final Search search = blockInfo.search;
			blockInfo.cornersMin.reset();
			blockInfo.cornersMax.reset();
			QueueCorner threadMin=localMin!=null?blockInfo.cornersMin:null;
			QueueCorner threadMax=localMax!=null?blockInfo.cornersMax:null;

			search.initialize(configuration,intensityImage,threadMin,threadMax);

			for (int iterY = iter0; iterY < iter1; iterY++) {
				// search for local peaks along this block row
				int y = border + iterY*step;
				int y1 = y + step;
				if( y1 > endY) y1 = endY;

				for(int x = border; x < endX; x += step ) {
					int x1 = x + step;
					if( x1 > endX) x1 = endX;
					search.searchBlock(x,y,x1,y1);
				}
			}
		});

		// Save results outside of the thread. This ensures the order is not randomized. That was wrecking havoc
		// on results that needed to be deterministic
		for (int i = 0; i < searches.size; i++) {
			SearchData data = searches.get(i);

			if( localMin != null )
				localMin.appendAll(data.cornersMin);
			if( localMax != null )
				localMax.appendAll(data.cornersMax);
		}
	}

	public SearchData createSearchData() {
		return new SearchData(search.newInstance());
	}

	protected static class SearchData {
		public final Search search;
		public final QueueCorner cornersMin = new QueueCorner();
		public final QueueCorner cornersMax = new QueueCorner();

		public SearchData(Search search) {
			this.search = search;
		}
	}
}