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- /*
- * 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 System.Collections.Generic;
-
- using ZXing.Common;
-
- namespace ZXing.QrCode.Internal
- {
- /// <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.</p>
- ///
- /// </summary>
- /// <author> Sean Owen
- /// </author>
- /// <author>www.Redivivus.in (suraj.supekar@redivivus.in) - Ported from ZXING Java Source
- /// </author>
- sealed class AlignmentPatternFinder
- {
- private readonly BitMatrix image;
- private readonly IList<AlignmentPattern> possibleCenters;
- private readonly int startX;
- private readonly int startY;
- private readonly int width;
- private readonly int height;
- private readonly float moduleSize;
- private readonly int[] crossCheckStateCount;
- private readonly 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 List<AlignmentPattern>(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>
- 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[j, i])
- {
- j++;
- }
- int currentState = 0;
- while (j < maxJ)
- {
- if (image[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 possibleCenters[0];
- }
-
- return null;
- }
-
- /// <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)
- {
- var result = (end - stateCount[2]) - stateCount[1] / 2.0f;
- if (Single.IsNaN(result))
- return null;
- return result;
- }
-
- /// <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 maxVariance = moduleSize / 2.0f;
- for (int i = 0; i < 3; i++)
- {
- if (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>
- /// <param name="originalStateCountTotal">The original state count total.</param>
- /// <returns>
- /// vertical center of alignment pattern, or null if not found
- /// </returns>
- private float? crossCheckVertical(int startI, int centerJ, int maxCount, int originalStateCountTotal)
- {
- 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[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 null;
- }
- while (i >= 0 && !image[centerJ, i] && stateCount[0] <= maxCount)
- {
- stateCount[0]++;
- i--;
- }
- if (stateCount[0] > maxCount)
- {
- return null;
- }
-
- // Now also count down from center
- i = startI + 1;
- while (i < maxI && image[centerJ, i] && stateCount[1] <= maxCount)
- {
- stateCount[1]++;
- i++;
- }
- if (i == maxI || stateCount[1] > maxCount)
- {
- return null;
- }
- while (i < maxI && !image[centerJ, i] && stateCount[2] <= maxCount)
- {
- stateCount[2]++;
- i++;
- }
- if (stateCount[2] > maxCount)
- {
- return null;
- }
-
- int stateCountTotal = stateCount[0] + stateCount[1] + stateCount[2];
- if (5 * Math.Abs(stateCountTotal - originalStateCountTotal) >= 2 * originalStateCountTotal)
- {
- return null;
- }
-
- return foundPatternCross(stateCount) ? centerFromEnd(stateCount, i) : null;
- }
-
- /// <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);
- if (centerJ == null)
- return null;
- float? centerI = crossCheckVertical(i, (int)centerJ, 2 * stateCount[1], stateCountTotal);
- if (centerI != null)
- {
- float estimatedModuleSize = (stateCount[0] + stateCount[1] + stateCount[2]) / 3.0f;
- foreach (var center in possibleCenters)
- {
- // Look for about the same center and module size:
- if (center.aboutEquals(estimatedModuleSize, centerI.Value, centerJ.Value))
- {
- return center.combineEstimate(centerI.Value, centerJ.Value, estimatedModuleSize);
- }
- }
- // Hadn't found this before; save it
- var point = new AlignmentPattern(centerJ.Value, centerI.Value, estimatedModuleSize);
- possibleCenters.Add(point);
- if (resultPointCallback != null)
- {
- resultPointCallback(point);
- }
- }
- return null;
- }
- }
- }
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