Listing 3 The getZoomedInCoords() subroutine 
sub getZoomedInCoords {
  # The Cartesian vector ($x, $y) corresponds to a point in the
  # *overview* map
  #
  my ( $x, $y ) = @_;

  # Scale and translate the input Cartesian vector to the Cartesian
  # vector corresponding to the top-left and bottom-right corners of
  # the frame in the *detailed* map
  #
  $x = ( $x * RATIO_X ) - HALF_WIDTH;
  $y = ( $y * RATIO_Y ) - HALF_HEIGHT;

  # Make sure that the point coordinates are inside the image
  # boundaries
  #
  if ( $x < 0 ) {
    $x = 0;
  }
  elsif ( $x > ( ZOOM_IN_WIDTH - CROP_WIDTH ) ) {
    $x = ZOOM_IN_WIDTH - CROP_WIDTH;
  }

  if ( $y < 0 ) {
	$y = 0;
    }
    elsif ( $y > ( ZOOM_IN_HEIGHT - CROP_HEIGHT ) ) {
	$y = ZOOM_IN_HEIGHT - CROP_HEIGHT;
    }

  # Return the top-left and bottom-right coordinates of the bounding box
  #  
  return ( $x, $y, $x+CROP_WIDTH, $y+CROP_HEIGHT );
}

