pathfind.js

// Pathfind.js
// Written by Ashley Gullen
// Copyright (c) 2013 Scirra Ltd.

// A* pathfinding javascript implementation
"use strict";

(function() {
	
	var PF_CLEAR = 0;
	var PF_OBSTACLE = 32767;
	
	function node()
	{
		this.parent = null;
		
		this.x = 0;
		this.y = 0;

		this.f = 0;
		this.g = 0;
		this.h = 0;
	};
	
	var nodeCache = [];			// for recycling nodes
	
	function allocNode()
	{
		var ret;
		
		if (nodeCache.length)
			ret = nodeCache.pop();
		else
			ret = new node();
			
		ret.parent = null;
		ret.x = 0;
		ret.y = 0;
		ret.f = 0;
		ret.g = 0;
		ret.h = 0;
		return ret;
	};
	
	function freeNode(n)
	{
		if (nodeCache.length < 64000)
			nodeCache.push(n);
	};
	
	function resultNode(x_, y_)
	{
		this.x = x_ || 0;
		this.y = y_ || 0;
	};
	
	var resultNodeCache = [];			// for recycling resultNodes
	
	function allocResultNode()
	{
		if (resultNodeCache.length)
			return resultNodeCache.pop();
		else
			return new resultNode(0, 0);
	};
	
	function freeResultNode(n)
	{
		if (resultNodeCache.length < 10000)
			resultNodeCache.push(n);
	};
	
	var workersSupported = (typeof Worker !== "undefined");
	var isInWebWorker = (typeof document === "undefined");		// no DOM in a worker
	var myInstance = null;										// single pathfinder instance for worker
	
	if (isInWebWorker)
	{
		self.addEventListener("message", function (e)
		{
			var d = e.data;
			
			if (!d)
				return;		// could be empty postMessage() to start worker
			
			if (d.cmd === "init")
			{
				if (!myInstance)
					myInstance = new pathfinder();
					
				myInstance.init(d.hcells, d.vcells, d.data, d.diagonals);
			}
			else if (d.cmd === "find")
			{
				// receive a pathfind job, process it them dispatch result
				myInstance.pathEnd.parent = null;
				myInstance.targetX = d.endX;
				myInstance.targetY = d.endY;
				
				if (myInstance.doLongFindPath(d.startX, d.startY))
				{
					self.postMessage({ cmd: "result", pathList: myInstance.pathList });
				}
				else
				{
					self.postMessage({ cmd: "result", pathList: null });
				}
			}
			
		}, false);
	}
	
	function pathfinder()
	{
		this.hcells = 0;
		this.vcells = 0;
		
		this.pathEnd = allocNode();
		
		this.cells = null;
		this.openList = [];
		this.closedList = [];
		this.closedCache = {};
		this.pathList = [];
		
		this.currentNode = null;
		this.targetX = 0;
		this.targetY = 0;
		this.diagonalsEnabled = true;
		
		this.worker = null;
		this.workerQueue = [];		// jobs awaiting completion from worker in order of requests made
		this.workerRecycle = [];
		
		var self = this;
		var i, len;
		
		if (workersSupported && !isInWebWorker)
		{
			// Create worker and receive results of pathfind jobs from it
			this.worker = new Worker("pathfind.js");
			
			this.worker.addEventListener("message", function (e) {
			
				if (!e || !e.data)
					return;
				
				if (e.data.cmd === "result")
				{
					if (e.data.pathList)
					{
						for (i = 0, len = self.pathList.length; i < len; i++)
							freeResultNode(self.pathList[i]);
						
						self.pathList = e.data.pathList;
						self.workerQueue[0].success();
					}
					else
						self.workerQueue[0].fail();
						
					self.workerRecycle.push(self.workerQueue.shift());
				}
			}, false);
			
			this.worker.addEventListener("error", function (e) {
				console.error(e);
			}, false);
			
			this.worker.postMessage(null);
		}
	};
	
	pathfinder.prototype.init = function (hcells_, vcells_, data_, diagonals_)
	{
		this.hcells = hcells_;
		this.vcells = vcells_;
		this.cells = data_;
		this.diagonalsEnabled = diagonals_;
		
		if (workersSupported && !isInWebWorker)
		{
			this.worker.postMessage({
				cmd: "init",
				hcells: hcells_,
				vcells: vcells_,
				diagonals: diagonals_,
				data: data_
			});
		}
	};
	
	pathfinder.prototype.isReady = function ()
	{
		return !!this.cells;
	};
	
	pathfinder.prototype.at = function (x_, y_)
	{
		if (x_ < 0 || y_ < 0 || x_ >= this.hcells || y_ >= this.vcells)
			return PF_OBSTACLE;
			
		return this.cells[x_][y_];
	};
	
	pathfinder.prototype.findPath = function (startX, startY, endX, endY, successCallback, failCallback)
	{
		if (!this.cells)
		{
			// not yet initialised
			failCallback();
			return;
		}
		
		startX = Math.floor(startX);
		startY = Math.floor(startY);
		endX = Math.floor(endX);
		endY = Math.floor(endY);
		
		this.targetX = endX;
		this.targetY = endY;
		this.pathEnd.parent = null;
		
		// Check the box made by the start and dest cells.
		// If the complete box is empty, allow a direct move to target.
		var minX = Math.min(startX, endX);
		var maxX = Math.max(startX, endX);
		var minY = Math.min(startY, endY);
		var maxY = Math.max(startY, endY);
		
		// Path goes out of bounds: no calculable path
		if (minX < 0 || minY < 0 || maxX >= this.hcells || maxY >= this.vcells)
		{
			failCallback();
			return;
		}
		
		var x, y, i, len, c, h, n;

		if (this.diagonalsEnabled)
		{
			var canMoveDirect = true;
			
			for (x = minX; x <= maxX; x++)
			{
				for (y = minY; y <= maxY; y++)
				{
					if (this.cells[x][y] !== 0)
					{
						canMoveDirect = false;
						
						// Break both loops
						x = maxX + 1;
						break;
					}
				}
			}

			// A "direct" path is available (box is empty)
			if (canMoveDirect)
			{
				for (i = 0, len = this.pathList.length; i < len; i++)
					freeResultNode(this.pathList[i]);
				this.pathList.length = 0;
			
				this.pathEnd.x = endX;
				this.pathEnd.y = endY;
				this.pathEnd.parent = null;
				n = allocResultNode();
				n.x = endX;
				n.y = endY;
				this.pathList.push(n);
				successCallback();
				return;
			}
		}
		
		if (workersSupported)
		{
			// recycle objects in the worker queue
			if (this.workerRecycle.length)
				h = this.workerRecycle.pop();
			else
				h = {};
			
			h.success = successCallback;
			h.fail = failCallback;
			
			// dispatch the heavy lifting to the worker thread
			this.workerQueue.push(h);

			this.worker.postMessage({
				cmd: "find",
				startX: startX,
				startY: startY,
				endX: endX,
				endY: endY
			});
		}
		else
		{
			// no web worker support, just run on main thread
			if (this.doLongFindPath(startX, startY))
				successCallback();
			else
				failCallback();
		}
	};
		
	pathfinder.prototype.doLongFindPath = function (startX, startY)
	{
		var i, len, c, n, p, lastDir = 8, curDir = -1, addNode;
		for (i = 0, len = this.openList.length; i < len; i++)
			freeNode(this.openList[i]);
		for (i = 0, len = this.closedList.length; i < len; i++)
			freeNode(this.closedList[i]);
		for (i = 0, len = this.pathList.length; i < len; i++)
			freeResultNode(this.pathList[i]);
		this.openList.length = 0;
		this.closedList.length = 0;
		this.closedCache = {};
		this.pathList.length = 0;

		// Add the start node to the open list
		var startNode = allocNode();
		startNode.x = startX;
		startNode.y = startY;

		this.openList.push(startNode);
		var obsLeft = false, obsTop = false, obsRight = false, obsBottom = false;
		var diagonals = this.diagonalsEnabled;
		
		// While there are nodes on the open list
		while (this.openList.length)
		{
			// Move the best F value to closed list
			c = this.openList.shift();
			this.closedList.unshift(c);
			this.closedCache[((c.x << 16) + c.y).toString()] = true;

			// Are we there yet?
			if (c.x === this.targetX && c.y === this.targetY)
			{
				this.pathEnd.parent = c.parent;
				this.pathEnd.x = c.x;
				this.pathEnd.y = c.y;
				
				// Link up the whole path to an indexable array
				p = this.pathEnd;
				
				while (p)
				{
					// filter redundant nodes in straight lines
					if (this.pathList.length === 0)
					{
						addNode = true;
						
						if (p.parent)
						{
							lastDir = this.nodeDirection(p, p.parent);
							curDir = lastDir;
						}
					}
					else if (!p.parent)
						addNode = false;
					else 
					{
						curDir = this.nodeDirection(p, p.parent);
						addNode = (curDir !== lastDir);
					}
					
					if (addNode)
					{
						n = allocResultNode();
						n.x = p.x;
						n.y = p.y;
						this.pathList.unshift(n);
						lastDir = curDir;
					}
					
					p = p.parent;
				}
				
				return true;
			}

			// Get current node
			this.currentNode = c;
			var x = c.x;
			var y = c.y;
			
			var obsLeft = (this.at(x - 1, y) === PF_OBSTACLE);
			var obsTop = (this.at(x, y - 1) === PF_OBSTACLE);
			var obsRight = (this.at(x + 1, y) === PF_OBSTACLE);
			var obsBottom = (this.at(x, y + 1) === PF_OBSTACLE);

			// Check adjacent 8 nodes.  No diagonals allowed if either cell being crossed is obstacle.
			if (!obsLeft)
				this.addCellToOpenList(x - 1, y, 10);

			if (diagonals && !obsLeft && !obsTop)
				this.addCellToOpenList(x - 1, y - 1, 14);

			if (!obsTop)
				this.addCellToOpenList(x, y - 1, 10);

			if (diagonals && !obsTop && !obsRight)
				this.addCellToOpenList(x + 1, y - 1, 14);

			if (!obsRight)
				this.addCellToOpenList(x + 1, y, 10);

			if (diagonals && !obsRight && !obsBottom)
				this.addCellToOpenList(x + 1, y + 1, 14);

			if (!obsBottom)
				this.addCellToOpenList(x, y + 1, 10);

			if (diagonals && !obsBottom && !obsLeft)
				this.addCellToOpenList(x - 1, y + 1, 14);
		}
		
		return false;
	};
	
	pathfinder.prototype.insertToOpenList = function (c)
	{
		var i, len;
		
		// Needs to go at end
		if (c.f >= this.openList[this.openList.length - 1].f)
		{
			this.openList.push(c);
		}
		else
		{
			for (i = 0, len = this.openList.length; i < len; i++)
			{
				if (c.f < this.openList[i].f)
				{
					this.openList.splice(i, 0, c);
					break;
				}
			}
		}
	};
	
	pathfinder.prototype.addCellToOpenList = function (x_, y_, g_)
	{
		// Ignore if cell on closed list
		if (this.closedCache.hasOwnProperty(((x_ << 16) + y_).toString()))
			return;
		
		var i, len, c;
		
		// Cell costs can be increased by changing the number in the map
		var curCellCost = this.at(x_, y_);

		// Is this cell already on the open list?
		for (i = 0, len = this.openList.length; i < len; i++)
		{
			c = this.openList[i];
			
			if (x_ === c.x && y_ === c.y)
			{
				// Is this a better path?
				if (this.currentNode.g + g_ + curCellCost < c.g)
				{
					// Update F, G and H and update parent
					c.parent = this.currentNode;
					c.g = this.currentNode.g + g_ + curCellCost;
					c.h = this.estimateH(c.x, c.y);
					c.f = c.g + c.h;

					// This node's F has changed:  Delete it then re-insert it in the right place

					if (this.openList.length === 1)
					{
						// no need to remove then re-insert same node, just leave it there
						return;
					}
					
					this.openList.splice(i, 1);
					this.insertToOpenList(c);
				}

				return;
			}
		}

		// Not on the open list; add it in the right place
		c = allocNode();
		c.x = x_;
		c.y = y_;
		c.h = this.estimateH(x_, y_);
		c.g = this.currentNode.g + g_ + curCellCost;
		c.f = c.h + c.g;
		c.parent = this.currentNode;

		// Insert this node sorted in the open list
		// The loop below won't add new largest F values
		if (!this.openList.length)
		{
			this.openList.push(c);
			return;
		}
		
		this.insertToOpenList(c);
	};
	
	function quickAbs(x)
	{
		return x < 0 ? -x : x;
	};
	
	pathfinder.prototype.estimateH = function (x_, y_)
	{
		var dx = quickAbs(x_ - this.targetX);
		var dy = quickAbs(y_ - this.targetY);

		return dx * 10 + dy * 10;
	};
	
	pathfinder.prototype.nodeDirection = function (a, b)
	{
		var ax = a.x;
		var ay = a.y;
		var bx = b.x;
		var by = b.y;

		if (ax === bx)
		{
			if (by > ay) return 6;
			if (by < ay) return 2;
			if (ay == by) return 8;
		}
		else if (ay === by)
		{
			if (bx > ax) return 4;
			if (by < ax) return 0;
		}
		else
		{
			if (bx < ax && by < ay) return 1;
			if (bx > ax && by < ay) return 3;
			if (bx < ax && by > ay) return 7;
			if (bx > ax && by > ay) return 5;
		}
		return 8;
	};
	
	if (!isInWebWorker)
	{
		window.PF_CLEAR = PF_CLEAR;
		window.PF_OBSTACLE = PF_OBSTACLE;
		window.Pathfinder = pathfinder;
		
		window.ResultNode = resultNode;
		window.allocResultNode = allocResultNode;
		window.freeResultNode = freeResultNode;
	}

})();