core/src/com/google/zxing/qrcode/encoder/MaskUtil.java

/*
 * Copyright 2008 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.
 */

package com.google.zxing.qrcode.encoder;

/**
 * @author Satoru Takabayashi
 * @author Daniel Switkin
 * @author Sean Owen
 */
final class MaskUtil {

  // Penalty weights from section 6.8.2.1
  private static final int N1 = 3;
  private static final int N2 = 3;
  private static final int N3 = 40;
  private static final int N4 = 10;

  private MaskUtil() {
    // do nothing
  }

  /**
   * Apply mask penalty rule 1 and return the penalty. Find repetitive cells with the same color and
   * give penalty to them. Example: 00000 or 11111.
   */
  static int applyMaskPenaltyRule1(ByteMatrix matrix) {
    return applyMaskPenaltyRule1Internal(matrix, true) + applyMaskPenaltyRule1Internal(matrix, false);
  }

  /**
   * Apply mask penalty rule 2 and return the penalty. Find 2x2 blocks with the same color and give
   * penalty to them. This is actually equivalent to the spec's rule, which is to find MxN blocks and give a
   * penalty proportional to (M-1)x(N-1), because this is the number of 2x2 blocks inside such a block.
   */
  static int applyMaskPenaltyRule2(ByteMatrix matrix) {
    int penalty = 0;
    byte[][] array = matrix.getArray();
    int width = matrix.getWidth();
    int height = matrix.getHeight();
    for (int y = 0; y < height - 1; y++) {
      for (int x = 0; x < width - 1; x++) {
        int value = array[y][x];
        if (value == array[y][x + 1] && value == array[y + 1][x] && value == array[y + 1][x + 1]) {
          penalty++;
        }
      }
    }
    return N2 * penalty;
  }

  /**
   * Apply mask penalty rule 3 and return the penalty. Find consecutive runs of 1:1:3:1:1:4
   * starting with black, or 4:1:1:3:1:1 starting with white, and give penalty to them.  If we
   * find patterns like 000010111010000, we give penalty once.
   */
  static int applyMaskPenaltyRule3(ByteMatrix matrix) {
    int numPenalties = 0;
    byte[][] array = matrix.getArray();
    int width = matrix.getWidth();
    int height = matrix.getHeight();
    for (int y = 0; y < height; y++) {
      for (int x = 0; x < width; x++) {
        byte[] arrayY = array[y];  // We can at least optimize this access
        if (x + 6 < width &&
            (x == 0 || arrayY[x-1] == 0) &&
            arrayY[x] == 1 &&
            arrayY[x +  1] == 0 &&
            arrayY[x +  2] == 1 &&
            arrayY[x +  3] == 1 &&
            arrayY[x +  4] == 1 &&
            arrayY[x +  5] == 0 &&
            arrayY[x +  6] == 1 &&
            (x + 7 >= width || arrayY[x+7] == 0) &&
            ((x + 10 < width &&
                arrayY[x +  7] == 0 &&
                arrayY[x +  8] == 0 &&
                arrayY[x +  9] == 0 &&
                arrayY[x + 10] == 0) ||
                (x - 4 >= 0 &&
                    arrayY[x -  1] == 0 &&
                    arrayY[x -  2] == 0 &&
                    arrayY[x -  3] == 0 &&
                    arrayY[x -  4] == 0))) {
          numPenalties++;
        }
        if (y + 6 < height &&
            (y == 0 || array[y-1][x] == 0) &&
            array[y][x] == 1  &&
            array[y +  1][x] == 0  &&
            array[y +  2][x] == 1  &&
            array[y +  3][x] == 1  &&
            array[y +  4][x] == 1  &&
            array[y +  5][x] == 0  &&
            array[y +  6][x] == 1 &&
            (y + 7 >= height || array[y+7][x] == 0) &&
            ((y + 10 < height &&
                array[y +  7][x] == 0 &&
                array[y +  8][x] == 0 &&
                array[y +  9][x] == 0 &&
                array[y + 10][x] == 0) ||
                (y - 4 >= 0 &&
                    array[y -  1][x] == 0 &&
                    array[y -  2][x] == 0 &&
                    array[y -  3][x] == 0 &&
                    array[y -  4][x] == 0))) {
          numPenalties++;
        }
      }
    }
    return numPenalties * N3;
  }

  /**
   * Apply mask penalty rule 4 and return the penalty. Calculate the ratio of dark cells and give
   * penalty if the ratio is far from 50%. It gives 10 penalty for 5% distance.
   */
  static int applyMaskPenaltyRule4(ByteMatrix matrix) {
    int numDarkCells = 0;
    byte[][] array = matrix.getArray();
    int width = matrix.getWidth();
    int height = matrix.getHeight();
    for (int y = 0; y < height; y++) {
      byte[] arrayY = array[y];
      for (int x = 0; x < width; x++) {
        if (arrayY[x] == 1) {
          numDarkCells++;
        }
      }
    }
    int numTotalCells = matrix.getHeight() * matrix.getWidth();
    int fivePercentVariances = Math.abs(numDarkCells * 2 - numTotalCells) * 10 / numTotalCells;
    return fivePercentVariances * N4;
  }

  /**
   * Return the mask bit for "getMaskPattern" at "x" and "y". See 8.8 of JISX0510:2004 for mask
   * pattern conditions.
   */
  static boolean getDataMaskBit(int maskPattern, int x, int y) {
    int intermediate;
    int temp;
    switch (maskPattern) {
      case 0:
        intermediate = (y + x) & 0x1;
        break;
      case 1:
        intermediate = y & 0x1;
        break;
      case 2:
        intermediate = x % 3;
        break;
      case 3:
        intermediate = (y + x) % 3;
        break;
      case 4:
        intermediate = ((y >>> 1) + (x / 3)) & 0x1;
        break;
      case 5:
        temp = y * x;
        intermediate = (temp & 0x1) + (temp % 3);
        break;
      case 6:
        temp = y * x;
        intermediate = ((temp & 0x1) + (temp % 3)) & 0x1;
        break;
      case 7:
        temp = y * x;
        intermediate = ((temp % 3) + ((y + x) & 0x1)) & 0x1;
        break;
      default:
        throw new IllegalArgumentException("Invalid mask pattern: " + maskPattern);
    }
    return intermediate == 0;
  }

  /**
   * Helper function for applyMaskPenaltyRule1. We need this for doing this calculation in both
   * vertical and horizontal orders respectively.
   */
  private static int applyMaskPenaltyRule1Internal(ByteMatrix matrix, boolean isHorizontal) {
    int penalty = 0;
    int iLimit = isHorizontal ? matrix.getHeight() : matrix.getWidth();
    int jLimit = isHorizontal ? matrix.getWidth() : matrix.getHeight();
    byte[][] array = matrix.getArray();
    for (int i = 0; i < iLimit; i++) {
      int numSameBitCells = 0;
      int prevBit = -1;
      for (int j = 0; j < jLimit; j++) {
        int bit = isHorizontal ? array[i][j] : array[j][i];
        if (bit == prevBit) {
          numSameBitCells++;
        } else {
          if (numSameBitCells >= 5) {
            penalty += N1 + (numSameBitCells - 5);
          }
          numSameBitCells = 1;  // Include the cell itself.
          prevBit = bit;
        }
      }
      if (numSameBitCells >= 5) {
        penalty += N1 + (numSameBitCells - 5);
      }
    }
    return penalty;
  }

}