zxing/csharp/qrcode/detector/Detector.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 com.google.zxing;
using com.google.zxing.common;

namespace com.google.zxing.qrcode.detector
{
    using Version = com.google.zxing.qrcode.decoder.Version;    

    public sealed class Detector
    { 
          private  MonochromeBitmapSource image;

          public Detector(MonochromeBitmapSource image) {
            this.image = image;
          }

          /**
           * <p>Detects a QR Code in an image, simply.</p>
           *
           * @return {@link DetectorResult} encapsulating results of detecting a QR Code
           * @throws ReaderException if no QR Code can be found
           */
          public DetectorResult detect(){
              try{
                return detect(null);
              }catch(Exception e){
                throw new ReaderException(e.Message);
              }           
          }

          /**
           * <p>Detects a QR Code in an image, simply.</p>
           *
           * @param hints optional hints to detector
           * @return {@link DetectorResult} encapsulating results of detecting a QR Code
           * @throws ReaderException if no QR Code can be found
           */
          public DetectorResult detect(System.Collections.Hashtable hints) {

            MonochromeBitmapSource image = this.image;
            if (!BlackPointEstimationMethod.TWO_D_SAMPLING.Equals(image.getLastEstimationMethod())) {
              image.estimateBlackPoint(BlackPointEstimationMethod.TWO_D_SAMPLING, 0);
            }

            FinderPatternFinder finder = new FinderPatternFinder(image);
            FinderPatternInfo info = finder.find(hints);

            FinderPattern topLeft = info.getTopLeft();
            FinderPattern topRight = info.getTopRight();
            FinderPattern bottomLeft = info.getBottomLeft();

            float moduleSize = calculateModuleSize(topLeft, topRight, bottomLeft);
            if (moduleSize < 1.0f) {
              throw new ReaderException();
            }
            int dimension = computeDimension(topLeft, topRight, bottomLeft, moduleSize);

            Version provisionalVersion = Version.getProvisionalVersionForDimension(dimension);
            int modulesBetweenFPCenters = provisionalVersion.getDimensionForVersion() - 7;

            AlignmentPattern alignmentPattern = null;
            // Anything above version 1 has an alignment pattern
            if (provisionalVersion.getAlignmentPatternCenters().Length > 0) {

              // Guess where a "bottom right" finder pattern would have been
              float bottomRightX = topRight.getX() - topLeft.getX() + bottomLeft.getX();
              float bottomRightY = topRight.getY() - topLeft.getY() + bottomLeft.getY();

              // Estimate that alignment pattern is closer by 3 modules
              // from "bottom right" to known top left location
              float correctionToTopLeft = 1.0f - 3.0f / (float) modulesBetweenFPCenters;
              int estAlignmentX = (int) (topLeft.getX() + correctionToTopLeft * (bottomRightX - topLeft.getX()));
              int estAlignmentY = (int) (topLeft.getY() + correctionToTopLeft * (bottomRightY - topLeft.getY()));

              // Kind of arbitrary -- expand search radius before giving up
              for (int i = 4; i <= 16; i <<= 1) {
                try {
                  alignmentPattern = findAlignmentInRegion(moduleSize,
                      estAlignmentX,
                      estAlignmentY,
                      (float) i);
                  break;
                } catch (ReaderException re) {
                  // try next round
                }
              }
              if (alignmentPattern == null) {
                throw new ReaderException();
              }

            }

            BitMatrix bits = sampleGrid(image, topLeft, topRight, bottomLeft, alignmentPattern, dimension);

            ResultPoint[] points;
            if (alignmentPattern == null) {
              points = new ResultPoint[]{bottomLeft, topLeft, topRight};
            } else {
              points = new ResultPoint[]{bottomLeft, topLeft, topRight, alignmentPattern};
            }
            return new DetectorResult(bits, points);
          }

          private static BitMatrix sampleGrid(MonochromeBitmapSource image,
                                              ResultPoint topLeft,
                                              ResultPoint topRight,
                                              ResultPoint bottomLeft,
                                              ResultPoint alignmentPattern,
                                              int dimension) {
            float dimMinusThree = (float) dimension - 3.5f;
            float bottomRightX;
            float bottomRightY;
            float sourceBottomRightX;
            float sourceBottomRightY;
            if (alignmentPattern != null) {
              bottomRightX = alignmentPattern.getX();
              bottomRightY = alignmentPattern.getY();
              sourceBottomRightX = sourceBottomRightY = dimMinusThree - 3.0f;
            } else {
              // Don't have an alignment pattern, just make up the bottom-right point
              bottomRightX = (topRight.getX() - topLeft.getX()) + bottomLeft.getX();
              bottomRightY = (topRight.getY() - topLeft.getY()) + bottomLeft.getY();
              sourceBottomRightX = sourceBottomRightY = dimMinusThree;
            }

            GridSampler sampler = GridSampler.Instance;
            return sampler.sampleGrid(
                image,
                dimension,
                3.5f,
                3.5f,
                dimMinusThree,
                3.5f,
                sourceBottomRightX,
                sourceBottomRightY,
                3.5f,
                dimMinusThree,
                topLeft.getX(),
                topLeft.getY(),
                topRight.getX(),
                topRight.getY(),
                bottomRightX,
                bottomRightY,
                bottomLeft.getX(),
                bottomLeft.getY());
          }

          /**
           * <p>Computes the dimension (number of modules on a size) of the QR Code based on the position
           * of the finder patterns and estimated module size.</p>
           */
          private static int computeDimension(ResultPoint topLeft,
                                              ResultPoint topRight,
                                              ResultPoint bottomLeft,
                                              float moduleSize) {
            int tltrCentersDimension = round(GenericResultPoint.distance(topLeft, topRight) / moduleSize);
            int tlblCentersDimension = round(GenericResultPoint.distance(topLeft, bottomLeft) / moduleSize);
            int dimension = ((tltrCentersDimension + tlblCentersDimension) >> 1) + 7;
            switch (dimension & 0x03) { // mod 4
              case 0:
                dimension++;
                break;
                // 1? do nothing
              case 2:
                dimension--;
                break;
              case 3:
                throw new ReaderException();
            }
            return dimension;
          }

          /**
           * <p>Computes an average estimated module size based on estimated derived from the positions
           * of the three finder patterns.</p>
           */
          private float calculateModuleSize(ResultPoint topLeft, ResultPoint topRight, ResultPoint bottomLeft) {
            // Take the average
            return (calculateModuleSizeOneWay(topLeft, topRight) +
                calculateModuleSizeOneWay(topLeft, bottomLeft)) / 2.0f;
          }

          /**
           * <p>Estimates module size based on two finder patterns -- it uses
           * {@link #sizeOfBlackWhiteBlackRunBothWays(int, int, int, int)} to figure the
           * width of each, measuring along the axis between their centers.</p>
           */
          private float calculateModuleSizeOneWay(ResultPoint pattern, ResultPoint otherPattern) {
            float moduleSizeEst1 = sizeOfBlackWhiteBlackRunBothWays((int) pattern.getX(),
                (int) pattern.getY(),
                (int) otherPattern.getX(),
                (int) otherPattern.getY());
            float moduleSizeEst2 = sizeOfBlackWhiteBlackRunBothWays((int) otherPattern.getX(),
                (int) otherPattern.getY(),
                (int) pattern.getX(),
                (int) pattern.getY());
            if (Single.IsNaN(moduleSizeEst1)) {
              return moduleSizeEst2;
            }
            if (Single.IsNaN(moduleSizeEst2))
            {
              return moduleSizeEst1;
            }
            // Average them, and divide by 7 since we've counted the width of 3 black modules,
            // and 1 white and 1 black module on either side. Ergo, divide sum by 14.
            return (moduleSizeEst1 + moduleSizeEst2) / 14.0f;
          }

          /**
           * See {@link #sizeOfBlackWhiteBlackRun(int, int, int, int)}; computes the total width of
           * a finder pattern by looking for a black-white-black run from the center in the direction
           * of another point (another finder pattern center), and in the opposite direction too.</p>
           */
          private float sizeOfBlackWhiteBlackRunBothWays(int fromX, int fromY, int toX, int toY) {

            float result = sizeOfBlackWhiteBlackRun(fromX, fromY, toX, toY);

            // Now count other way -- don't run off image though of course
            int otherToX = fromX - (toX - fromX);
            if (otherToX < 0) {
              // "to" should the be the first value not included, so, the first value off
              // the edge is -1
              otherToX = -1;
            } else if (otherToX >= image.getWidth()) {
              otherToX = image.getWidth();
            }
            int otherToY = fromY - (toY - fromY);
            if (otherToY < 0) {
              otherToY = -1;
            } else if (otherToY >= image.getHeight()) {
              otherToY = image.getHeight();
            }
            result += sizeOfBlackWhiteBlackRun(fromX, fromY, otherToX, otherToY);
            return result - 1.0f; // -1 because we counted the middle pixel twice
          }

          /**
           * <p>This method traces a line from a point in the image, in the direction towards another point.
           * It begins in a black region, and keeps going until it finds white, then black, then white again.
           * It reports the distance from the start to this point.</p>
           *
           * <p>This is used when figuring out how wide a finder pattern is, when the finder pattern
           * may be skewed or rotated.</p>
           */
          private float sizeOfBlackWhiteBlackRun(int fromX, int fromY, int toX, int toY) {
            // Mild variant of Bresenham's algorithm;
            // see http://en.wikipedia.org/wiki/Bresenham's_line_algorithm
            bool steep = Math.Abs(toY - fromY) > Math.Abs(toX - fromX);
            if (steep) {
              int temp = fromX;
              fromX = fromY;
              fromY = temp;
              temp = toX;
              toX = toY;
              toY = temp;
            }

            int dx = Math.Abs(toX - fromX);
            int dy = Math.Abs(toY - fromY);
            int error = -dx >> 1;
            int ystep = fromY < toY ? 1 : -1;
            int xstep = fromX < toX ? 1 : -1;
            int state = 0; // In black pixels, looking for white, first or second time
            int diffX =0;
            int diffY =0;

            for (int x = fromX, y = fromY; x != toX; x += xstep) {

              int realX = steep ? y : x;
              int realY = steep ? x : y;
              if (state == 1) { // In white pixels, looking for black
                if (image.isBlack(realX, realY)) {
                  state++;
                }
              } else {
                if (!image.isBlack(realX, realY)) {
                  state++;
                }
              }

              if (state == 3) { // Found black, white, black, and stumbled back onto white; done
                diffX = x - fromX;
                diffY = y - fromY;
                return (float) Math.Sqrt((double) (diffX * diffX + diffY * diffY));
              }
              error += dy;
              if (error > 0) {
                y += ystep;
                error -= dx;
              }
            }

            diffX = toX - fromX;
            diffY = toY - fromY;
            return (float) Math.Sqrt((double) (diffX * diffX + diffY * diffY));
          }

          /**
           * <p>Attempts to locate an alignment pattern in a limited region of the image, which is
           * guessed to contain it. This method uses {@link AlignmentPattern}.</p>
           *
           * @param overallEstModuleSize estimated module size so far
           * @param estAlignmentX x coordinate of center of area probably containing alignment pattern
           * @param estAlignmentY y coordinate of above
           * @param allowanceFactor number of pixels in all directons to search from the center
           * @return {@link AlignmentPattern} if found, or null otherwise
           * @throws ReaderException if an unexpected error occurs during detection
           */
          private AlignmentPattern findAlignmentInRegion(float overallEstModuleSize,
                                                         int estAlignmentX,
                                                         int estAlignmentY,
                                                         float allowanceFactor){
            // Look for an alignment pattern (3 modules in size) around where it
            // should be
            int allowance = (int) (allowanceFactor * overallEstModuleSize);
            int alignmentAreaLeftX = Math.Max(0, estAlignmentX - allowance);
            int alignmentAreaRightX = Math.Min(image.getWidth() - 1, estAlignmentX + allowance);
            if (alignmentAreaRightX - alignmentAreaLeftX < overallEstModuleSize * 3) {
              throw new ReaderException();
            }

            int alignmentAreaTopY = Math.Max(0, estAlignmentY - allowance);
            int alignmentAreaBottomY = Math.Min(image.getHeight() - 1, estAlignmentY + allowance);

            AlignmentPatternFinder alignmentFinder =
                new AlignmentPatternFinder(
                    image,
                    alignmentAreaLeftX,
                    alignmentAreaTopY,
                    alignmentAreaRightX - alignmentAreaLeftX,
                    alignmentAreaBottomY - alignmentAreaTopY,
                    overallEstModuleSize);
            return alignmentFinder.find();
          }

          /**
           * Ends up being a bit faster than Math.round(). This merely rounds its argument to the nearest int,
           * where x.5 rounds up.
           */
          private static int round(float d) {
            return (int) (d + 0.5f);
          }
    
    }


}