code: public function getImportantPartFromLegacyMode(ImageInterface $image, $mode): ImportantPartInterface
      {
          if (1 !== substr_count($mode, '_')) {
              throw new \InvalidArgumentException(sprintf('"%s" is not a legacy resize mode', $mode));
          }
  
          $importantPart = [
              0,
              0,
              $image->getDimensions()->getSize()->getWidth(),
              $image->getDimensions()->getSize()->getHeight(),
          ];
  
          [$modeX, $modeY] = explode('_', $mode);
  
          if ('left' === $modeX) {
              $importantPart[2] = 1;
          } elseif ('right' === $modeX) {
              $importantPart[0] = $importantPart[2] - 1;
              $importantPart[2] = 1;
          }
  
          if ('top' === $modeY) {
              $importantPart[3] = 1;
          } elseif ('bottom' === $modeY) {
              $importantPart[1] = $importantPart[3] - 1;
              $importantPart[3] = 1;
          }
  
          return new ImportantPart(
              new Point($importantPart[0], $importantPart[1]),
              new Box($importantPart[2], $importantPart[3])
          );
      }
docs: {@inheritdoc}