add extra cost for turns in A* to avoid staircase

lib/pathfinding-browser.js

@@ -1208,6 +1208,7 @@ function AStarFinder(opt) {
     this.dontCrossCorners = opt.dontCrossCorners;
     this.heuristic = opt.heuristic || Heuristic.manhattan;
     this.weight = opt.weight || 1;
+    this.avoidStaircase = opt.avoidStaircase;
 }
 
 /**
@@ -1224,8 +1225,10 @@ AStarFinder.prototype.findPath = function(startX, startY, endX, endY, grid) {
         heuristic = this.heuristic,
         allowDiagonal = this.allowDiagonal,
         dontCrossCorners = this.dontCrossCorners,
+        avoidStaircase = this.avoidStaircase,
         weight = this.weight,
         abs = Math.abs, SQRT2 = Math.SQRT2,
+        turnPenalty = 1, lastDirection = undefined, 
         node, neighbors, neighbor, i, l, x, y, ng;
 
     // set the `g` and `f` value of the start node to be 0
@@ -1263,6 +1266,14 @@ AStarFinder.prototype.findPath = function(startX, startY, endX, endY, grid) {
             // and calculate the next g score
             ng = node.g + ((x - node.x === 0 || y - node.y === 0) ? 1 : SQRT2);
 
+
+            if (avoidStaircase) {
+            	// add additional cost if neighbor creates a turn
+                lastDirection = node.parent == undefined? undefined : { x : node.x - node.parent.x, y : node.y - node.parent.y };
+                var turned = lastDirection == undefined? 0 : lastDirection.x != x - node.x || lastDirection.y != y - node.y;
+                ng += turnPenalty * turned;
+            }
+
             // check if the neighbor has not been inspected yet, or
             // can be reached with smaller cost from the current node
             if (!neighbor.opened || ng < neighbor.g) {
@@ -2006,4 +2017,4 @@ require.define("/PathFinding.js", function (require, module, exports, __dirname,
 
 });
 require("/PathFinding.js");
-return require("/PathFinding");})();
+return require("/PathFinding");})();

visual/index.html

@@ -70,6 +70,8 @@ <h3>Options</h3>
             <label class="option_label">Bi-directional</label> <br>
             <input type="checkbox" class="dont_cross_corners">
             <label class="option_label">Don't Cross Corners</label> <br>
+            <input type="checkbox" class="avoid_staircase">
+            <label class="option_label">Avoid staircase</label> <br>
             <input class="spinner" name="astar_weight" value="1">
             <label class="option_label">Weight</label> <br>
           </div>

visual/js/panel.js

@@ -41,6 +41,8 @@ var Panel = {
                                      '.bi-directional:checked').val() !=='undefined';
             dontCrossCorners = typeof $('#astar_section ' +
                                      '.dont_cross_corners:checked').val() !=='undefined';
+            avoidStaircase = typeof $('#astar_section ' +
+                                     '.avoid_staircase:checked').val() !=='undefined';
 
             /* parseInt returns NaN (which is falsy) if the string can't be parsed */
             weight = parseInt($('#astar_section .spinner').val()) || 1;
@@ -59,7 +61,8 @@ var Panel = {
                     allowDiagonal: allowDiagonal,
                     dontCrossCorners: dontCrossCorners,
                     heuristic: PF.Heuristic[heuristic],
-                    weight: weight
+                    weight: weight, 
+                    avoidStaircase: avoidStaircase
                 });
             }
             break;