dispatchRect method

@override Uint8List dispatchRect(Uint8List data, int width, int height, Rect rect,)

Implementation

@override
Uint8List dispatchRect(Uint8List data, int width, int height, Rect rect) {
  final newByte = Uint8List.fromList(data);

  int offsetX, offsetY;
  final random = math.Random();
  if (random.nextDouble() > 0.5) {
    offsetX = (random.nextDouble() * -2 * maxOffsetXRange + maxOffsetXRange)
        .toInt();
    offsetY = 0;
  } else {
    offsetX = 0;
    offsetY = (random.nextDouble() * -2 * maxOffsetYRange + maxOffsetYRange)
        .toInt();
  }

  for (int i = rect.top; i < rect.bottom; i++) {
    for (int j = rect.left; j < rect.right; j++) {
      int offset;
      int current;

      //从右下角开始copy
      if (offsetX >= 0 && offsetY >= 0) {
        offset = (rect.bottom - i + rect.top - offsetY) * width +
            rect.right +
            rect.left -
            j -
            offsetX;
        current =
            (rect.bottom + rect.top - i) * width + rect.right + rect.left - j;

        if ((rect.bottom - i) < offsetY || (rect.right - j) < offsetX) {
          newByte[current] = 255;
        } else {
          newByte[current] = newByte[offset];
        }
      }

      //从右上角开始copy
      if (offsetX >= 0 && offsetY <= 0) {
        offset = (i - offsetY) * width + rect.right + rect.left - j - offsetX;
        current = i * width + rect.right + rect.left - j;

        if (i > (rect.bottom + offsetY) || (rect.right - j) < offsetX) {
          newByte[current] = 255;
        } else {
          newByte[current] = newByte[offset];
        }
      }

      //从左下角开始copy
      if (offsetX <= 0 && offsetY >= 0) {
        offset = (rect.bottom + rect.top - i - offsetY) * width + j - offsetX;
        current = (rect.bottom + rect.top - i) * width + j;

        if ((rect.bottom - i) < offsetY || j > (rect.right + offsetX)) {
          newByte[current] = 255;
        } else {
          newByte[current] = newByte[offset];
        }
      }

      //从左上角开始copy
      if (offsetX <= 0 && offsetY <= 0) {
        offset = (i - offsetY) * width + j - offsetX;
        current = i * width + j;

        if (i > (rect.bottom + offsetY) || j > (rect.right + offsetX)) {
          newByte[current] = 255;
        } else {
          newByte[current] = newByte[offset];
        }
      }
    }
  }
  return newByte;
}