BorderTraversingAlgorithm.java

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 * Copyright (c) 2015 - 2017
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package jsettlers.algorithms.traversing.borders;

import jsettlers.algorithms.interfaces.IContainingProvider;
import jsettlers.common.movable.EDirection;
import jsettlers.common.position.ShortPoint2D;
import jsettlers.common.utils.mutables.MutableInt;

/**
 * 
 * @author Andreas Eberle
 */
public final class BorderTraversingAlgorithm {

	/**
	 * No instances of this class shall be created.
	 */
	private BorderTraversingAlgorithm() {
	}

	public static boolean traverseBorder(final IContainingProvider containingProvider, final ShortPoint2D startPos, final IBorderVisitor visitor, boolean visitOutside) {
		return traverseBorder(containingProvider, startPos, visitor, visitOutside, new MutableInt());
	}

	/**
	 * Traverses the border of an area defined by the given {@link IContainingProvider} starting at insideStartPosition. The given visitor is called
	 * for every position on the outside of the area.<br>
	 * If the insideStartPosition is not surrounded by any position that is not in the area (meaning insideStartPosition is not on the border), the
	 * traversing can't be started and the visitor is never called.
	 *
	 * @param containingProvider
	 *            {@link IContainingProvider} defining the position that are in and the ones that are outside the area.
	 * @param insideStartPosition
	 *            The start position for the traversing. This position must be in the area but at the border!
	 * @param visitor
	 *            The visitor that will be called for every border position (a border position is a position outside the border!).
	 * @param visitOutside
	 *            If true the positions on the outside will be visited.<br>
	 *            If false the inside positions will be visited.
	 * @param traversedPositions
	 *            This object will contain the number of traversed positions after the call.
	 * @return true if the whole border has been traversed.<br>
	 *         false if the traversing has been canceled by the {@link IBorderVisitor}'s visit() method.
	 */
	public static boolean traverseBorder(final IContainingProvider containingProvider, final ShortPoint2D insideStartPosition,
			final IBorderVisitor visitor, boolean visitOutside, MutableInt traversedPositions) {

		ShortPoint2D outsideStartPosition = findOutsidePosition(insideStartPosition, containingProvider);

		return traverseBorder(containingProvider, insideStartPosition, outsideStartPosition, visitor, visitOutside, traversedPositions);
	}

	/**
	 * Traverses the border of an area defined by the given {@link IContainingProvider} starting at the two neighbors insideStartPosition and
	 * outsideStartPosition. The given visitor is called for every position on the outside of the area.<br>
	 * 
	 * @param containingProvider
	 *            {@link IContainingProvider} defining the position that are in and the ones that are outside the area.
	 * @param insideStartPosition
	 *            The inside start position for the traversing. This position must be in the area but at the border!
	 * @param outsideStartPosition
	 *            The outside start position for the traversing. This position must be outside the area but at the border and a direct neighbor of
	 *            insideStartPosition
	 * @param visitor
	 *            The visitor that will be called for every border position (a border position is a position outside the border!).
	 * @param visitOutside
	 *            If true the positions on the outside will be visited.<br>
	 *            If false the inside positions will be visited.
	 * @param traversedPositions
	 *            This object will contain the number of traversed positions after the call.
	 * @return true if the whole border has been traversed.<br>
	 *         false if the traversing has been canceled by the {@link IBorderVisitor}'s visit() method.
	 */
	public static boolean traverseBorder(IContainingProvider containingProvider, ShortPoint2D insideStartPosition, ShortPoint2D outsideStartPosition,
			final IBorderVisitor visitor, boolean visitOutside, MutableInt traversedPositions) {

		final int startInsideX = insideStartPosition.x;
		final int startInsideY = insideStartPosition.y;

		final int startOutsideX = outsideStartPosition.x;
		final int startOutsideY = outsideStartPosition.y;

		if (!visitor.visit(startInsideX, startInsideY, startOutsideX, startOutsideY)) {
			traversedPositions.value = 1;
			return false;
		}

		int insideX = startInsideX;
		int insideY = startInsideY;

		int outsideX = startOutsideX;
		int outsideY = startOutsideY;

		int traversedPositionsCounter = 1;

		do {
			traversedPositionsCounter++;

			EDirection outInDir = EDirection.getDirection(insideX - outsideX, insideY - outsideY);
			EDirection neighborDir = outInDir.getNeighbor(-1);

			int neighborX = neighborDir.gridDeltaX + outsideX;
			int neighborY = neighborDir.gridDeltaY + outsideY;

			if (containingProvider.contains(neighborX, neighborY)) {
				insideX = neighborX;
				insideY = neighborY;

				if (!visitOutside && !visitor.visit(insideX, insideY, outsideX, outsideY)) {
					traversedPositions.value = traversedPositionsCounter;
					return false;
				}
			} else {
				outsideX = neighborX;
				outsideY = neighborY;

				if (visitOutside && !visitor.visit(insideX, insideY, outsideX, outsideY)) {
					traversedPositions.value = traversedPositionsCounter;
					return false;
				}
			}
		} while (insideX != startInsideX || insideY != startInsideY || outsideX != startOutsideX
				|| outsideY != startOutsideY);

		traversedPositions.value = traversedPositionsCounter;
		return true;
	}

	private static ShortPoint2D findOutsidePosition(ShortPoint2D insideStartPosition, IContainingProvider containingProvider) {
		// determine first outside position
		for (EDirection dir : EDirection.VALUES) {
			int outsideX = (int) insideStartPosition.x + dir.gridDeltaX;
			int outsideY = (int) insideStartPosition.y + dir.gridDeltaY;

			if (!containingProvider.contains(outsideX, outsideY)) {
				return new ShortPoint2D(outsideX, outsideY);
			}
		}

		return null; // no neighbor of the start position is on the outside.
	}
}