/silverlight/qrcode/detector/AlignmentPatternFinder.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 ReaderException = com.google.zxing.ReaderException;

using ResultPoint = com.google.zxing.ResultPoint;

using ResultPointCallback = com.google.zxing.ResultPointCallback;

using BitMatrix = com.google.zxing.common.BitMatrix;

namespace com.google.zxing.qrcode.detector

{

	

	/// <summary> <p>This class attempts to find alignment patterns in a QR Code. Alignment patterns look like finder

	/// patterns but are smaller and appear at regular intervals throughout the image.</p>

	/// 

	/// <p>At the moment this only looks for the bottom-right alignment pattern.</p>

	/// 

	/// <p>This is mostly a simplified copy of {@link FinderPatternFinder}. It is copied,

	/// pasted and stripped down here for maximum performance but does unfortunately duplicate

	/// some 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>

	sealed class AlignmentPatternFinder

	{

		

		//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;

		//UPGRADE_NOTE: Final was removed from the declaration of 'startX '. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1003'"

		private int startX;

		//UPGRADE_NOTE: Final was removed from the declaration of 'startY '. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1003'"

		private int startY;

		//UPGRADE_NOTE: Final was removed from the declaration of 'width '. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1003'"

		private int width;

		//UPGRADE_NOTE: Final was removed from the declaration of 'height '. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1003'"

		private int height;

		//UPGRADE_NOTE: Final was removed from the declaration of 'moduleSize '. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1003'"

		private float moduleSize;

		//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 look in a portion of the whole image.</p>

		/// 

		/// </summary>

		/// <param name="image">image to search

		/// </param>

		/// <param name="startX">left column from which to start searching

		/// </param>

		/// <param name="startY">top row from which to start searching

		/// </param>

		/// <param name="width">width of region to search

		/// </param>

		/// <param name="height">height of region to search

		/// </param>

		/// <param name="moduleSize">estimated module size so far

		/// </param>

		internal AlignmentPatternFinder(BitMatrix image, int startX, int startY, int width, int height, float moduleSize, ResultPointCallback resultPointCallback)

		{

			this.image = image;

			this.possibleCenters = new System.Collections.Generic.List<Object>(5);

			this.startX = startX;

			this.startY = startY;

			this.width = width;

			this.height = height;

			this.moduleSize = moduleSize;

			this.crossCheckStateCount = new int[3];

			this.resultPointCallback = resultPointCallback;

		}

		

		/// <summary> <p>This method attempts to find the bottom-right alignment pattern in the image. It is a bit messy since

		/// it's pretty performance-critical and so is written to be fast foremost.</p>

		/// 

		/// </summary>

		/// <returns> {@link AlignmentPattern} if found

		/// </returns>

		/// <throws>  ReaderException if not found </throws>

		internal AlignmentPattern find()

		{

			int startX = this.startX;

			int height = this.height;

			int maxJ = startX + width;

			int 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

			int[] stateCount = new int[3];

			for (int iGen = 0; iGen < height; iGen++)

			{

				// Search from middle outwards

				int i = middleI + ((iGen & 0x01) == 0?((iGen + 1) >> 1):- ((iGen + 1) >> 1));

				stateCount[0] = 0;

				stateCount[1] = 0;

				stateCount[2] = 0;

				int 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.get_Renamed(j, i))

				{

					j++;

				}

				int currentState = 0;

				while (j < maxJ)

				{

					if (image.get_Renamed(j, i))

					{

						// Black pixel

						if (currentState == 1)

						{

							// Counting black pixels

							stateCount[currentState]++;

						}

						else

						{

							// Counting white pixels

							if (currentState == 2)

							{

								// A winner?

								if (foundPatternCross(stateCount))

								{

									// Yes

									AlignmentPattern confirmed = 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 (foundPatternCross(stateCount))

				{

					AlignmentPattern confirmed = 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 (!(possibleCenters.Count == 0))

			{

				return (AlignmentPattern) possibleCenters[0];

			}

			

			throw ReaderException.Instance;

		}

		

		/// <summary> Given a count of black/white/black pixels just seen and an end position,

		/// figures the location of the center of this black/white/black 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[2]) - stateCount[1] / 2.0f;

		}

		

		/// <param name="stateCount">count of black/white/black pixels just read

		/// </param>

		/// <returns> true iff the proportions of the counts is close enough to the 1/1/1 ratios

		/// used by alignment patterns to be considered a match

		/// </returns>

		private bool foundPatternCross(int[] stateCount)

		{

			float moduleSize = this.moduleSize;

			float maxVariance = moduleSize / 2.0f;

			for (int i = 0; i < 3; i++)

			{

				if (System.Math.Abs(moduleSize - stateCount[i]) >= maxVariance)

				{

					return false;

				}

			}

			return true;

		}

		

		/// <summary> <p>After a horizontal scan finds a potential alignment pattern, this method

		/// "cross-checks" by scanning down vertically through the center of the possible

		/// alignment pattern to see if the same proportion is detected.</p>

		/// 

		/// </summary>

		/// <param name="startI">row where an alignment pattern was detected

		/// </param>

		/// <param name="centerJ">center of the section that appears to cross an alignment 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 alignment 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;

			stateCount[0] = 0;

			stateCount[1] = 0;

			stateCount[2] = 0;

			

			// Start counting up from center

			int i = startI;

			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[1] <= maxCount)

			{

				stateCount[1]++;

				i++;

			}

			if (i == maxI || stateCount[1] > maxCount)

			{

				return System.Single.NaN;

			}

			while (i < maxI && !image.get_Renamed(centerJ, i) && stateCount[2] <= maxCount)

			{

				stateCount[2]++;

				i++;

			}

			if (stateCount[2] > maxCount)

			{

				return System.Single.NaN;

			}

			

			int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2];

			if (5 * System.Math.Abs(stateCountTotal - originalStateCountTotal) >= 2 * originalStateCountTotal)

			{

				return System.Single.NaN;

			}

			

			return foundPatternCross(stateCount)?centerFromEnd(stateCount, i):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 see if this pattern had been

		/// found on a previous horizontal scan. If so, we consider it confirmed and conclude we have

		/// found the alignment pattern.</p>

		/// 

		/// </summary>

		/// <param name="stateCount">reading state module counts from horizontal scan

		/// </param>

		/// <param name="i">row where alignment pattern may be found

		/// </param>

		/// <param name="j">end of possible alignment pattern in row

		/// </param>

		/// <returns> {@link AlignmentPattern} if we have found the same pattern twice, or null if not

		/// </returns>

		private AlignmentPattern handlePossibleCenter(int[] stateCount, int i, int j)

		{

			int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2];

			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, 2 * stateCount[1], stateCountTotal);

			if (!System.Single.IsNaN(centerI))

			{

				//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) (stateCount[0] + stateCount[1] + stateCount[2]) / 3.0f;

				int max = possibleCenters.Count;

				for (int index = 0; index < max; index++)

				{

					AlignmentPattern center = (AlignmentPattern) 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

				ResultPoint point = new AlignmentPattern(centerJ, centerI, estimatedModuleSize);

				possibleCenters.Add(point);

				if (resultPointCallback != null)

				{

					resultPointCallback.foundPossibleResultPoint(point);

				}

			}

			return null;

		}

	}

}