plantuml/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 satorux@google.com (Satoru Takabayashi) - creator
 * @author dswitkin@google.com (Daniel Switkin) - ported from C++
 */
public final class MaskUtil {

  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.
  public 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.
  public 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 += 3;
        }
      }
    }
    return penalty;
  }

  // Apply mask penalty rule 3 and return the penalty. Find consecutive cells of 00001011101 or
  // 10111010000, and give penalty to them.  If we find patterns like 000010111010000, we give
  // penalties twice (i.e. 40 * 2).
  public static int applyMaskPenaltyRule3(ByteMatrix matrix) {
    int penalty = 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) {
        // Tried to simplify following conditions but failed.
        if (x + 6 < width &&
            array[y][x] == 1 &&
            array[y][x +  1] == 0 &&
            array[y][x +  2] == 1 &&
            array[y][x +  3] == 1 &&
            array[y][x +  4] == 1 &&
            array[y][x +  5] == 0 &&
            array[y][x +  6] == 1 &&
            ((x + 10 < width &&
                array[y][x +  7] == 0 &&
                array[y][x +  8] == 0 &&
                array[y][x +  9] == 0 &&
                array[y][x + 10] == 0) ||
                (x - 4 >= 0 &&
                    array[y][x -  1] == 0 &&
                    array[y][x -  2] == 0 &&
                    array[y][x -  3] == 0 &&
                    array[y][x -  4] == 0))) {
          penalty += 40;
        }
        if (y + 6 < height &&
            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 + 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))) {
          penalty += 40;
        }
      }
    }
    return penalty;
  }

  // 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. Examples:
  // -   0% => 100
  // -  40% =>  20
  // -  45% =>  10
  // -  50% =>   0
  // -  55% =>  10
  // -  55% =>  20
  // - 100% => 100
  public 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) {
      for (int x = 0; x < width; ++x) {
        if (array[y][x] == 1) {
          numDarkCells += 1;
        }
      }
    }
    int numTotalCells = matrix.getHeight() * matrix.getWidth();
    double darkRatio = (double) numDarkCells / numTotalCells;
    return Math.abs((int) (darkRatio * 100 - 50)) / 5 * 10;
  }

  // Return the mask bit for "getMaskPattern" at "x" and "y". See 8.8 of JISX0510:2004 for mask
  // pattern conditions.
  public static boolean getDataMaskBit(int maskPattern, int x, int y) {
    if (!QRCode.isValidMaskPattern(maskPattern)) {
      throw new IllegalArgumentException("Invalid mask pattern");
    }
    int intermediate, 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 numSameBitCells = 0;
    int prevBit = -1;
    // Horizontal mode:
    //   for (int i = 0; i < matrix.height(); ++i) {
    //     for (int j = 0; j < matrix.width(); ++j) {
    //       int bit = matrix.get(i, j);
    // Vertical mode:
    //   for (int i = 0; i < matrix.width(); ++i) {
    //     for (int j = 0; j < matrix.height(); ++j) {
    //       int bit = matrix.get(j, i);
    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) {
      for (int j = 0; j < jLimit; ++j) {
        int bit = isHorizontal ? array[i][j] : array[j][i];
        if (bit == prevBit) {
          numSameBitCells += 1;
          // Found five repetitive cells with the same color (bit).
          // We'll give penalty of 3.
          if (numSameBitCells == 5) {
            penalty += 3;
          } else if (numSameBitCells > 5) {
            // After five repetitive cells, we'll add the penalty one
            // by one.
            penalty += 1;
          }
        } else {
          numSameBitCells = 1;  // Include the cell itself.
          prevBit = bit;
        }
      }
      numSameBitCells = 0;  // Clear at each row/column.
    }
    return penalty;
  }

}