alignpat.js

/*
  Ported to JavaScript by Lazar Laszlo 2011 
  
  lazarsoft@gmail.com, www.lazarsoft.info
  
*/

/*
*
* Copyright 2007 ZXing authors
*
* 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.
*/


function AlignmentPattern(posX, posY,  estimatedModuleSize)
{
	this.x=posX;
	this.y=posY;
	this.count = 1;
	this.estimatedModuleSize = estimatedModuleSize;
	
	this.__defineGetter__("EstimatedModuleSize", function()
	{
		return this.estimatedModuleSize;
	}); 
	this.__defineGetter__("Count", function()
	{
		return this.count;
	});
	this.__defineGetter__("X", function()
	{
		return Math.floor(this.x);
	});
	this.__defineGetter__("Y", function()
	{
		return Math.floor(this.y);
	});
	this.incrementCount = function()
	{
		this.count++;
	}
	this.aboutEquals=function( moduleSize,  i,  j)
		{
			if (Math.abs(i - this.y) <= moduleSize && Math.abs(j - this.x) <= moduleSize)
			{
				var moduleSizeDiff = Math.abs(moduleSize - this.estimatedModuleSize);
				return moduleSizeDiff <= 1.0 || moduleSizeDiff / this.estimatedModuleSize <= 1.0;
			}
			return false;
		}
	
}

function AlignmentPatternFinder( image,width,height,  startX,  startY, moduleSize,  resultPointCallback)
{
	this.image = image;
	this.possibleCenters = new Array();
	this.startX = startX;
	this.startY = startY;
	this.width = width;
	this.height = height;
	this.moduleSize = moduleSize;
	this.crossCheckStateCount = new Array(0,0,0);
	this.resultPointCallback = resultPointCallback;
	
	this.centerFromEnd=function(stateCount,  end)
		{
			return  (end - stateCount[2]) - stateCount[1] / 2.0;
		}
	this.foundPatternCross = function(stateCount)
		{
			var moduleSize = this.moduleSize;
			var maxVariance = moduleSize / 2.0;
			for (var i = 0; i < 3; i++)
			{
				if (Math.abs(moduleSize - stateCount[i]) >= maxVariance)
				{
					return false;
				}
			}
			return true;
		}

	this.crossCheckVertical=function( startI,  centerJ,  maxCount,  originalStateCountTotal)
		{
			var image = this.image;
			
			var maxI = this.height;
			var stateCount = this.crossCheckStateCount;
			stateCount[0] = 0;
			stateCount[1] = 0;
			stateCount[2] = 0;
			
			// Start counting up from center
			var i = startI;
			while (i >= 0 && image[centerJ + i*this.width] && stateCount[1] <= maxCount)
			{
				stateCount[1]++;
				i--;
			}
			// If already too many modules in this state or ran off the edge:
			if (i < 0 || stateCount[1] > maxCount)
			{
				return NaN;
			}
			while (i >= 0 && !image[centerJ + i*this.width] && stateCount[0] <= maxCount)
			{
				stateCount[0]++;
				i--;
			}
			if (stateCount[0] > maxCount)
			{
				return NaN;
			}
			
			// Now also count down from center
			i = startI + 1;
			while (i < maxI && image[centerJ + i*this.width] && stateCount[1] <= maxCount)
			{
				stateCount[1]++;
				i++;
			}
			if (i == maxI || stateCount[1] > maxCount)
			{
				return NaN;
			}
			while (i < maxI && !image[centerJ + i*this.width] && stateCount[2] <= maxCount)
			{
				stateCount[2]++;
				i++;
			}
			if (stateCount[2] > maxCount)
			{
				return NaN;
			}
			
			var stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2];
			if (5 * Math.abs(stateCountTotal - originalStateCountTotal) >= 2 * originalStateCountTotal)
			{
				return NaN;
			}
			
			return this.foundPatternCross(stateCount)?this.centerFromEnd(stateCount, i):NaN;
		}
		
	this.handlePossibleCenter=function( stateCount,  i,  j)
		{
			var stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2];
			var centerJ = this.centerFromEnd(stateCount, j);
			var centerI = this.crossCheckVertical(i, Math.floor (centerJ), 2 * stateCount[1], stateCountTotal);
			if (!isNaN(centerI))
			{
				var estimatedModuleSize = (stateCount[0] + stateCount[1] + stateCount[2]) / 3.0;
				var max = this.possibleCenters.length;
				for (var index = 0; index < max; index++)
				{
					var center =  this.possibleCenters[index];
					// Look for about the same center and module size:
					if (center.aboutEquals(estimatedModuleSize, centerI, centerJ))
					{
						return new AlignmentPattern(centerJ, centerI, estimatedModuleSize);
					}
				}
				// Hadn't found this before; save it
				var point = new AlignmentPattern(centerJ, centerI, estimatedModuleSize);
				this.possibleCenters.push(point);
				if (this.resultPointCallback != null)
				{
					this.resultPointCallback.foundPossibleResultPoint(point);
				}
			}
			return null;
		}
		
	this.find = function()
	{
			var startX = this.startX;
			var height = this.height;
			var maxJ = startX + width;
			var middleI = startY + (height >> 1);
			// We are looking for black/white/black modules in 1:1:1 ratio;
			// this tracks the number of black/white/black modules seen so far
			var stateCount = new Array(0,0,0);
			for (var iGen = 0; iGen < height; iGen++)
			{
				// Search from middle outwards
				var i = middleI + ((iGen & 0x01) == 0?((iGen + 1) >> 1):- ((iGen + 1) >> 1));
				stateCount[0] = 0;
				stateCount[1] = 0;
				stateCount[2] = 0;
				var j = startX;
				// Burn off leading white pixels before anything else; if we start in the middle of
				// a white run, it doesn't make sense to count its length, since we don't know if the
				// white run continued to the left of the start point
				while (j < maxJ && !image[j + this.width* i])
				{
					j++;
				}
				var currentState = 0;
				while (j < maxJ)
				{
					if (image[j + i*this.width])
					{
						// Black pixel
						if (currentState == 1)
						{
							// Counting black pixels
							stateCount[currentState]++;
						}
						else
						{
							// Counting white pixels
							if (currentState == 2)
							{
								// A winner?
								if (this.foundPatternCross(stateCount))
								{
									// Yes
									var confirmed = this.handlePossibleCenter(stateCount, i, j);
									if (confirmed != null)
									{
										return confirmed;
									}
								}
								stateCount[0] = stateCount[2];
								stateCount[1] = 1;
								stateCount[2] = 0;
								currentState = 1;
							}
							else
							{
								stateCount[++currentState]++;
							}
						}
					}
					else
					{
						// White pixel
						if (currentState == 1)
						{
							// Counting black pixels
							currentState++;
						}
						stateCount[currentState]++;
					}
					j++;
				}
				if (this.foundPatternCross(stateCount))
				{
					var confirmed = this.handlePossibleCenter(stateCount, i, maxJ);
					if (confirmed != null)
					{
						return confirmed;
					}
				}
			}
			
			// Hmm, nothing we saw was observed and confirmed twice. If we had
			// any guess at all, return it.
			if (!(this.possibleCenters.length == 0))
			{
				return  this.possibleCenters[0];
			}
			
			throw "Couldn't find enough alignment patterns";
		}
	
}