/silverlight/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.Generic.List<Object> 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.Generic.List<Object> 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 = new System.Collections.Generic.List<Object>(10);

			this.crossCheckStateCount = new int[5];

			this.resultPointCallback = resultPointCallback;

		}

		

		internal virtual FinderPatternInfo find(System.Collections.Generic.Dictionary<Object,Object> 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;

			}

		}

	}

}