zxing/csharp/qrcode/detector/FinderPatternFinder.cs

/*
* 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.
*/
using System;
using DecodeHintType = com.google.zxing.DecodeHintType;
using ReaderException = com.google.zxing.ReaderException;
using ResultPoint = com.google.zxing.ResultPoint;
using ResultPointCallback = com.google.zxing.ResultPointCallback;
using Collections = com.google.zxing.common.Collections;
using Comparator = com.google.zxing.common.Comparator;
using BitMatrix = com.google.zxing.common.BitMatrix;
namespace com.google.zxing.qrcode.detector
{
	
	/// <summary> <p>This class attempts to find finder patterns in a QR Code. Finder patterns are the square
	/// markers at three corners of a QR Code.</p>
	/// 
	/// <p>This class is thread-safe but not reentrant. Each thread must allocate its own object.
	/// 
	/// </summary>
	/// <author>  Sean Owen
	/// </author>
	/// <author>www.Redivivus.in (suraj.supekar@redivivus.in) - Ported from ZXING Java Source 
	/// </author>
	public class FinderPatternFinder
	{
		virtual protected internal BitMatrix Image
		{
			get
			{
				return image;
			}
			
		}
		virtual protected internal System.Collections.ArrayList PossibleCenters
		{
			get
			{
				return possibleCenters;
			}
			
		}
		private int[] CrossCheckStateCount
		{
			get
			{
				crossCheckStateCount[0] = 0;
				crossCheckStateCount[1] = 0;
				crossCheckStateCount[2] = 0;
				crossCheckStateCount[3] = 0;
				crossCheckStateCount[4] = 0;
				return crossCheckStateCount;
			}
			
		}
		
		private const int CENTER_QUORUM = 2;
		protected internal const int MIN_SKIP = 3; // 1 pixel/module times 3 modules/center
		protected internal const int MAX_MODULES = 57; // support up to version 10 for mobile clients
		private const int INTEGER_MATH_SHIFT = 8;
		
		//UPGRADE_NOTE: Final was removed from the declaration of 'image '. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1003'"
		private BitMatrix image;
		//UPGRADE_NOTE: Final was removed from the declaration of 'possibleCenters '. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1003'"
		private System.Collections.ArrayList possibleCenters;
		private bool hasSkipped;
		//UPGRADE_NOTE: Final was removed from the declaration of 'crossCheckStateCount '. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1003'"
		private int[] crossCheckStateCount;
		//UPGRADE_NOTE: Final was removed from the declaration of 'resultPointCallback '. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1003'"
		private ResultPointCallback resultPointCallback;
		
		/// <summary> <p>Creates a finder that will search the image for three finder patterns.</p>
		/// 
		/// </summary>
		/// <param name="image">image to search
		/// </param>
		public FinderPatternFinder(BitMatrix image):this(image, null)
		{
		}
		
		public FinderPatternFinder(BitMatrix image, ResultPointCallback resultPointCallback)
		{
			this.image = image;
			this.possibleCenters = System.Collections.ArrayList.Synchronized(new System.Collections.ArrayList(10));
			this.crossCheckStateCount = new int[5];
			this.resultPointCallback = resultPointCallback;
		}
		
		internal virtual FinderPatternInfo find(System.Collections.Hashtable hints)
		{
			bool tryHarder = hints != null && hints.ContainsKey(DecodeHintType.TRY_HARDER);
			int maxI = image.Height;
			int maxJ = image.Width;
			// We are looking for black/white/black/white/black modules in
			// 1:1:3:1:1 ratio; this tracks the number of such modules seen so far
			
			// Let's assume that the maximum version QR Code we support takes up 1/4 the height of the
			// image, and then account for the center being 3 modules in size. This gives the smallest
			// number of pixels the center could be, so skip this often. When trying harder, look for all
			// QR versions regardless of how dense they are.
			int iSkip = (3 * maxI) / (4 * MAX_MODULES);
			if (iSkip < MIN_SKIP || tryHarder)
			{
				iSkip = MIN_SKIP;
			}
			
			bool done = false;
			int[] stateCount = new int[5];
			for (int i = iSkip - 1; i < maxI && !done; i += iSkip)
			{
				// Get a row of black/white values
				stateCount[0] = 0;
				stateCount[1] = 0;
				stateCount[2] = 0;
				stateCount[3] = 0;
				stateCount[4] = 0;
				int currentState = 0;
				for (int j = 0; j < maxJ; j++)
				{
					if (image.get_Renamed(j, i))
					{
						// Black pixel
						if ((currentState & 1) == 1)
						{
							// Counting white pixels
							currentState++;
						}
						stateCount[currentState]++;
					}
					else
					{
						// White pixel
						if ((currentState & 1) == 0)
						{
							// Counting black pixels
							if (currentState == 4)
							{
								// A winner?
								if (foundPatternCross(stateCount))
								{
									// Yes
									bool confirmed = handlePossibleCenter(stateCount, i, j);
									if (confirmed)
									{
										// Start examining every other line. Checking each line turned out to be too
										// expensive and didn't improve performance.
										iSkip = 2;
										if (hasSkipped)
										{
											done = haveMultiplyConfirmedCenters();
										}
										else
										{
											int rowSkip = findRowSkip();
											if (rowSkip > stateCount[2])
											{
												// Skip rows between row of lower confirmed center
												// and top of presumed third confirmed center
												// but back up a bit to get a full chance of detecting
												// it, entire width of center of finder pattern
												
												// Skip by rowSkip, but back off by stateCount[2] (size of last center
												// of pattern we saw) to be conservative, and also back off by iSkip which
												// is about to be re-added
												i += rowSkip - stateCount[2] - iSkip;
												j = maxJ - 1;
											}
										}
									}
									else
									{
										// Advance to next black pixel
										do 
										{
											j++;
										}
										while (j < maxJ && !image.get_Renamed(j, i));
										j--; // back up to that last white pixel
									}
									// Clear state to start looking again
									currentState = 0;
									stateCount[0] = 0;
									stateCount[1] = 0;
									stateCount[2] = 0;
									stateCount[3] = 0;
									stateCount[4] = 0;
								}
								else
								{
									// No, shift counts back by two
									stateCount[0] = stateCount[2];
									stateCount[1] = stateCount[3];
									stateCount[2] = stateCount[4];
									stateCount[3] = 1;
									stateCount[4] = 0;
									currentState = 3;
								}
							}
							else
							{
								stateCount[++currentState]++;
							}
						}
						else
						{
							// Counting white pixels
							stateCount[currentState]++;
						}
					}
				}
				if (foundPatternCross(stateCount))
				{
					bool confirmed = handlePossibleCenter(stateCount, i, maxJ);
					if (confirmed)
					{
						iSkip = stateCount[0];
						if (hasSkipped)
						{
							// Found a third one
							done = haveMultiplyConfirmedCenters();
						}
					}
				}
			}
			
			FinderPattern[] patternInfo = selectBestPatterns();
			ResultPoint.orderBestPatterns(patternInfo);
			
			return new FinderPatternInfo(patternInfo);
		}
		
		/// <summary> Given a count of black/white/black/white/black pixels just seen and an end position,
		/// figures the location of the center of this run.
		/// </summary>
		private static float centerFromEnd(int[] stateCount, int end)
		{
			//UPGRADE_WARNING: Data types in Visual C# might be different.  Verify the accuracy of narrowing conversions. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1042'"
			return (float) (end - stateCount[4] - stateCount[3]) - stateCount[2] / 2.0f;
		}
		
		/// <param name="stateCount">count of black/white/black/white/black pixels just read
		/// </param>
		/// <returns> true iff the proportions of the counts is close enough to the 1/1/3/1/1 ratios
		/// used by finder patterns to be considered a match
		/// </returns>
		protected internal static bool foundPatternCross(int[] stateCount)
		{
			int totalModuleSize = 0;
			for (int i = 0; i < 5; i++)
			{
				int count = stateCount[i];
				if (count == 0)
				{
					return false;
				}
				totalModuleSize += count;
			}
			if (totalModuleSize < 7)
			{
				return false;
			}
			int moduleSize = (totalModuleSize << INTEGER_MATH_SHIFT) / 7;
			int maxVariance = moduleSize / 2;
			// Allow less than 50% variance from 1-1-3-1-1 proportions
			return System.Math.Abs(moduleSize - (stateCount[0] << INTEGER_MATH_SHIFT)) < maxVariance && System.Math.Abs(moduleSize - (stateCount[1] << INTEGER_MATH_SHIFT)) < maxVariance && System.Math.Abs(3 * moduleSize - (stateCount[2] << INTEGER_MATH_SHIFT)) < 3 * maxVariance && System.Math.Abs(moduleSize - (stateCount[3] << INTEGER_MATH_SHIFT)) < maxVariance && System.Math.Abs(moduleSize - (stateCount[4] << INTEGER_MATH_SHIFT)) < maxVariance;
		}
		
		/// <summary> <p>After a horizontal scan finds a potential finder pattern, this method
		/// "cross-checks" by scanning down vertically through the center of the possible
		/// finder pattern to see if the same proportion is detected.</p>
		/// 
		/// </summary>
		/// <param name="startI">row where a finder pattern was detected
		/// </param>
		/// <param name="centerJ">center of the section that appears to cross a finder pattern
		/// </param>
		/// <param name="maxCount">maximum reasonable number of modules that should be
		/// observed in any reading state, based on the results of the horizontal scan
		/// </param>
		/// <returns> vertical center of finder pattern, or {@link Float#NaN} if not found
		/// </returns>
		private float crossCheckVertical(int startI, int centerJ, int maxCount, int originalStateCountTotal)
		{
			BitMatrix image = this.image;
			
			int maxI = image.Height;
			int[] stateCount = CrossCheckStateCount;
			
			// Start counting up from center
			int i = startI;
			while (i >= 0 && image.get_Renamed(centerJ, i))
			{
				stateCount[2]++;
				i--;
			}
			if (i < 0)
			{
				return System.Single.NaN;
			}
			while (i >= 0 && !image.get_Renamed(centerJ, i) && 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 System.Single.NaN;
			}
			while (i >= 0 && image.get_Renamed(centerJ, i) && stateCount[0] <= maxCount)
			{
				stateCount[0]++;
				i--;
			}
			if (stateCount[0] > maxCount)
			{
				return System.Single.NaN;
			}
			
			// Now also count down from center
			i = startI + 1;
			while (i < maxI && image.get_Renamed(centerJ, i))
			{
				stateCount[2]++;
				i++;
			}
			if (i == maxI)
			{
				return System.Single.NaN;
			}
			while (i < maxI && !image.get_Renamed(centerJ, i) && stateCount[3] < maxCount)
			{
				stateCount[3]++;
				i++;
			}
			if (i == maxI || stateCount[3] >= maxCount)
			{
				return System.Single.NaN;
			}
			while (i < maxI && image.get_Renamed(centerJ, i) && stateCount[4] < maxCount)
			{
				stateCount[4]++;
				i++;
			}
			if (stateCount[4] >= maxCount)
			{
				return System.Single.NaN;
			}
			
			// If we found a finder-pattern-like section, but its size is more than 40% different than
			// the original, assume it's a false positive
			int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2] + stateCount[3] + stateCount[4];
			if (5 * System.Math.Abs(stateCountTotal - originalStateCountTotal) >= 2 * originalStateCountTotal)
			{
				return System.Single.NaN;
			}
			
			return foundPatternCross(stateCount)?centerFromEnd(stateCount, i):System.Single.NaN;
		}
		
		/// <summary> <p>Like {@link #crossCheckVertical(int, int, int, int)}, and in fact is basically identical,
		/// except it reads horizontally instead of vertically. This is used to cross-cross
		/// check a vertical cross check and locate the real center of the alignment pattern.</p>
		/// </summary>
		private float crossCheckHorizontal(int startJ, int centerI, int maxCount, int originalStateCountTotal)
		{
			BitMatrix image = this.image;
			
			int maxJ = image.Width;
			int[] stateCount = CrossCheckStateCount;
			
			int j = startJ;
			while (j >= 0 && image.get_Renamed(j, centerI))
			{
				stateCount[2]++;
				j--;
			}
			if (j < 0)
			{
				return System.Single.NaN;
			}
			while (j >= 0 && !image.get_Renamed(j, centerI) && stateCount[1] <= maxCount)
			{
				stateCount[1]++;
				j--;
			}
			if (j < 0 || stateCount[1] > maxCount)
			{
				return System.Single.NaN;
			}
			while (j >= 0 && image.get_Renamed(j, centerI) && stateCount[0] <= maxCount)
			{
				stateCount[0]++;
				j--;
			}
			if (stateCount[0] > maxCount)
			{
				return System.Single.NaN;
			}
			
			j = startJ + 1;
			while (j < maxJ && image.get_Renamed(j, centerI))
			{
				stateCount[2]++;
				j++;
			}
			if (j == maxJ)
			{
				return System.Single.NaN;
			}
			while (j < maxJ && !image.get_Renamed(j, centerI) && stateCount[3] < maxCount)
			{
				stateCount[3]++;
				j++;
			}
			if (j == maxJ || stateCount[3] >= maxCount)
			{
				return System.Single.NaN;
			}
			while (j < maxJ && image.get_Renamed(j, centerI) && stateCount[4] < maxCount)
			{
				stateCount[4]++;
				j++;
			}
			if (stateCount[4] >= maxCount)
			{
				return System.Single.NaN;
			}
			
			// If we found a finder-pattern-like section, but its size is significantly different than
			// the original, assume it's a false positive
			int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2] + stateCount[3] + stateCount[4];
			if (5 * System.Math.Abs(stateCountTotal - originalStateCountTotal) >= originalStateCountTotal)
			{
				return System.Single.NaN;
			}
			
			return foundPatternCross(stateCount)?centerFromEnd(stateCount, j):System.Single.NaN;
		}
		
		/// <summary> <p>This is called when a horizontal scan finds a possible alignment pattern. It will
		/// cross check with a vertical scan, and if successful, will, ah, cross-cross-check
		/// with another horizontal scan. This is needed primarily to locate the real horizontal
		/// center of the pattern in cases of extreme skew.</p>
		/// 
		/// <p>If that succeeds the finder pattern location is added to a list that tracks
		/// the number of times each location has been nearly-matched as a finder pattern.
		/// Each additional find is more evidence that the location is in fact a finder
		/// pattern center
		/// 
		/// </summary>
		/// <param name="stateCount">reading state module counts from horizontal scan
		/// </param>
		/// <param name="i">row where finder pattern may be found
		/// </param>
		/// <param name="j">end of possible finder pattern in row
		/// </param>
		/// <returns> true if a finder pattern candidate was found this time
		/// </returns>
		protected internal virtual bool handlePossibleCenter(int[] stateCount, int i, int j)
		{
			int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2] + stateCount[3] + stateCount[4];
			float centerJ = centerFromEnd(stateCount, j);
			//UPGRADE_WARNING: Data types in Visual C# might be different.  Verify the accuracy of narrowing conversions. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1042'"
			float centerI = crossCheckVertical(i, (int) centerJ, stateCount[2], stateCountTotal);
			if (!System.Single.IsNaN(centerI))
			{
				// Re-cross check
				//UPGRADE_WARNING: Data types in Visual C# might be different.  Verify the accuracy of narrowing conversions. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1042'"
				centerJ = crossCheckHorizontal((int) centerJ, (int) centerI, stateCount[2], stateCountTotal);
				if (!System.Single.IsNaN(centerJ))
				{
					//UPGRADE_WARNING: Data types in Visual C# might be different.  Verify the accuracy of narrowing conversions. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1042'"
					float estimatedModuleSize = (float) stateCountTotal / 7.0f;
					bool found = false;
					int max = possibleCenters.Count;
					for (int index = 0; index < max; index++)
					{
						FinderPattern center = (FinderPattern) possibleCenters[index];
						// Look for about the same center and module size:
						if (center.aboutEquals(estimatedModuleSize, centerI, centerJ))
						{
							center.incrementCount();
							found = true;
							break;
						}
					}
					if (!found)
					{
						ResultPoint point = new FinderPattern(centerJ, centerI, estimatedModuleSize);
						possibleCenters.Add(point);
						if (resultPointCallback != null)
						{
							resultPointCallback.foundPossibleResultPoint(point);
						}
					}
					return true;
				}
			}
			return false;
		}
		
		/// <returns> number of rows we could safely skip during scanning, based on the first
		/// two finder patterns that have been located. In some cases their position will
		/// allow us to infer that the third pattern must lie below a certain point farther
		/// down in the image.
		/// </returns>
		private int findRowSkip()
		{
			int max = possibleCenters.Count;
			if (max <= 1)
			{
				return 0;
			}
			FinderPattern firstConfirmedCenter = null;
			for (int i = 0; i < max; i++)
			{
				FinderPattern center = (FinderPattern) possibleCenters[i];
				if (center.Count >= CENTER_QUORUM)
				{
					if (firstConfirmedCenter == null)
					{
						firstConfirmedCenter = center;
					}
					else
					{
						// We have two confirmed centers
						// How far down can we skip before resuming looking for the next
						// pattern? In the worst case, only the difference between the
						// difference in the x / y coordinates of the two centers.
						// This is the case where you find top left last.
						hasSkipped = true;
						//UPGRADE_WARNING: Data types in Visual C# might be different.  Verify the accuracy of narrowing conversions. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1042'"
						return (int) (System.Math.Abs(firstConfirmedCenter.X - center.X) - System.Math.Abs(firstConfirmedCenter.Y - center.Y)) / 2;
					}
				}
			}
			return 0;
		}
		
		/// <returns> true iff we have found at least 3 finder patterns that have been detected
		/// at least {@link #CENTER_QUORUM} times each, and, the estimated module size of the
		/// candidates is "pretty similar"
		/// </returns>
		private bool haveMultiplyConfirmedCenters()
		{
			int confirmedCount = 0;
			float totalModuleSize = 0.0f;
			int max = possibleCenters.Count;
			for (int i = 0; i < max; i++)
			{
				FinderPattern pattern = (FinderPattern) possibleCenters[i];
				if (pattern.Count >= CENTER_QUORUM)
				{
					confirmedCount++;
					totalModuleSize += pattern.EstimatedModuleSize;
				}
			}
			if (confirmedCount < 3)
			{
				return false;
			}
			// OK, we have at least 3 confirmed centers, but, it's possible that one is a "false positive"
			// and that we need to keep looking. We detect this by asking if the estimated module sizes
			// vary too much. We arbitrarily say that when the total deviation from average exceeds
			// 5% of the total module size estimates, it's too much.
			//UPGRADE_WARNING: Data types in Visual C# might be different.  Verify the accuracy of narrowing conversions. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1042'"
			float average = totalModuleSize / (float) max;
			float totalDeviation = 0.0f;
			for (int i = 0; i < max; i++)
			{
				FinderPattern pattern = (FinderPattern) possibleCenters[i];
				totalDeviation += System.Math.Abs(pattern.EstimatedModuleSize - average);
			}
			return totalDeviation <= 0.05f * totalModuleSize;
		}
		
		/// <returns> the 3 best {@link FinderPattern}s from our list of candidates. The "best" are
		/// those that have been detected at least {@link #CENTER_QUORUM} times, and whose module
		/// size differs from the average among those patterns the least
		/// </returns>
		/// <throws>  ReaderException if 3 such finder patterns do not exist </throws>
		private FinderPattern[] selectBestPatterns()
		{
			
			int startSize = possibleCenters.Count;
			if (startSize < 3)
			{
				// Couldn't find enough finder patterns
				throw ReaderException.Instance;
			}
			
			// Filter outlier possibilities whose module size is too different
			if (startSize > 3)
			{
				// But we can only afford to do so if we have at least 4 possibilities to choose from
				float totalModuleSize = 0.0f;
				for (int i = 0; i < startSize; i++)
				{
					totalModuleSize += ((FinderPattern) possibleCenters[i]).EstimatedModuleSize;
				}
				//UPGRADE_WARNING: Data types in Visual C# might be different.  Verify the accuracy of narrowing conversions. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1042'"
				float average = totalModuleSize / (float) startSize;
				for (int i = 0; i < possibleCenters.Count && possibleCenters.Count > 3; i++)
				{
					FinderPattern pattern = (FinderPattern) possibleCenters[i];
					if (System.Math.Abs(pattern.EstimatedModuleSize - average) > 0.2f * average)
					{
						possibleCenters.RemoveAt(i);
						i--;
					}
				}
			}
			
			if (possibleCenters.Count > 3)
			{
				// Throw away all but those first size candidate points we found.
				Collections.insertionSort(possibleCenters, new CenterComparator());
				SupportClass.SetCapacity(possibleCenters, 3);
			}
			
			return new FinderPattern[]{(FinderPattern) possibleCenters[0], (FinderPattern) possibleCenters[1], (FinderPattern) possibleCenters[2]};
		}
		
		/// <summary> <p>Orders by {@link FinderPattern#getCount()}, descending.</p></summary>
		private class CenterComparator : Comparator
		{
			public virtual int compare(System.Object center1, System.Object center2)
			{
				return ((FinderPattern) center2).Count - ((FinderPattern) center1).Count;
			}
		}
	}
}