DiagonalHeuristic.java

package vooga.towerdefense.model.AStar;

import java.awt.Point;

/**
 * Calculate the diagonal distance to goal when
 * a straight step costs 1 and diagonal step costs sqrt(2).
 */
public class DiagonalHeuristic implements AStarHeuristic {

        public float getEstimatedDistanceToGoal(Point start, Point goal) {              
               
                float h_diagonal = (float) Math.min(Math.abs(start.x-goal.x), Math.abs(start.y-goal.y));
                float h_straight = (float) (Math.abs(start.x-goal.x) + Math.abs(start.y-goal.y));
                float h_result = (float) (Math.sqrt(2) * h_diagonal + (h_straight - 2*h_diagonal));
               
                /**
                 * Breaking ties: Adding a small value to the heuristic to avoid A* fully searching all equal length paths
                 * We only want 1 shortest path, not all of them.
                 *
                 * @param p The small value we add to the heuristic. Should be p < (minimum cost of taking one step) / (expected maximum path length) to avoid
                 */
               
                float p = (1/10000);
                h_result *= (1.0 + p);
               
                return h_result;
        }

}