findCornerFromCenter method

ResultPoint findCornerFromCenter(int centerX, int deltaX, int left, int right, int centerY, int deltaY, int top, int bottom, int maxWhiteRun,)

Attempts to locate a corner of the barcode by scanning up, down, left or right from a center point which should be within the barcode.

@param centerX center's x component (horizontal) @param deltaX same as deltaY but change in x per step instead @param left minimum value of x @param right maximum value of x @param centerY center's y component (vertical) @param deltaY change in y per step. If scanning up this is negative; down, positive; left or right, 0 @param top minimum value of y to search through (meaningless when di == 0) @param bottom maximum value of y @param maxWhiteRun maximum run of white pixels that can still be considered to be within the barcode @return a ResultPoint encapsulating the corner that was found @throws NotFoundException if such a point cannot be found

Implementation

ResultPoint findCornerFromCenter(
  int centerX,
  int deltaX,
  int left,
  int right,
  int centerY,
  int deltaY,
  int top,
  int bottom,
  int maxWhiteRun,
) {
  List<int>? lastRange;
  for (int y = centerY, x = centerX;
      y < bottom && y >= top && x < right && x >= left;
      y += deltaY, x += deltaX) {
    List<int>? range;
    if (deltaX == 0) {
      // horizontal slices, up and down
      range = blackWhiteRange(y, maxWhiteRun, left, right, true);
    } else {
      // vertical slices, left and right
      range = blackWhiteRange(x, maxWhiteRun, top, bottom, false);
    }
    if (range == null) {
      if (lastRange == null) {
        throw NotFoundException.instance;
      }
      // lastRange was found
      if (deltaX == 0) {
        final lastY = y - deltaY;
        if (lastRange[0] < centerX) {
          if (lastRange[1] > centerX) {
            // straddle, choose one or the other based on direction
            return ResultPoint(
              lastRange[deltaY > 0 ? 0 : 1].toDouble(),
              lastY.toDouble(),
            );
          }
          return ResultPoint(lastRange[0].toDouble(), lastY.toDouble());
        } else {
          return ResultPoint(lastRange[1].toDouble(), lastY.toDouble());
        }
      } else {
        final lastX = x - deltaX;
        if (lastRange[0] < centerY) {
          if (lastRange[1] > centerY) {
            return ResultPoint(
              lastX.toDouble(),
              lastRange[deltaX < 0 ? 0 : 1].toDouble(),
            );
          }
          return ResultPoint(lastX.toDouble(), lastRange[0].toDouble());
        } else {
          return ResultPoint(lastX.toDouble(), lastRange[1].toDouble());
        }
      }
    }
    lastRange = range;
  }
  throw NotFoundException.instance;
}