#!/bin/sh
#
# hole_fill_shepards [options]  image_in  image_out
#
# Using a fast shepards diffusion locate and fill a transparent hole, using
# only the colors found around the very edge of a hole.  Existing non-opaque
# colors in an image are not effected.
#
# For details see IM Examples,  "Sparse Color as a Fill Operator"
#    http://www.imagemagick.org/Usage/canvas/#sparse_fill
# and the following section "Shepard's, a Blur Alturnative"
#
# Options
#
#   -t pixels   Edge Thickness. Sometimes the edge colors are not uniform
#               enough, in which case a thicker edge to select colors for
#               filling works better.
#
#   -b          Background fill. Do not trim to just edge pixels.
#               This is needed when the 'hole' is the surrounding background
#               and you are filling outward, rather than inward.
#
# WARNING: This assumes that only a single, or set of closely related holes
# are present in the image, as shepards method know no boundaries.  As such
# the edge colors of one hole may cross a thin boundary to effect the fill
# colors into a neaghbouring hole.
#
# I hope to be able to replace this with a proper 'Diffusion' color filling
# technique, when such a function is added via Morphology methods.
#
###
#
# Anthony Thyssen,    September 2010
#
PROGNAME=`type $0 | awk '{print $3}'`  # search for executable on path
PROGDIR=`dirname $PROGNAME`            # extract directory of program
PROGNAME=`basename $PROGNAME`          # base name of program
Usage() {
  echo >&2 "$PROGNAME:" "$@"
  sed >&2 -n '/^###/q; /^#/!q; s/^#//; s/^ //; 3s/^/Usage: /; 2,$ p' \
          "$PROGDIR/$PROGNAME"
  exit 10;
}

thickness=1       # Thickness of the edge pixels (EG: Disk:1.4 )
trim="-trim"      # Trim the image to just the edge pixels (inward fill)

while [  $# -gt 0 ]; do
  case "$1" in

  # Standard help option.
  --help|--doc*) Usage ;;

  -b) trim=-noop ;;                             # outward background fill
  -t) shift                                     # edge thickness
      thickness=`expr + "$1" : '^\([1-9][0-9]*\)$'` ||
         Usage "Invalid Thickness"
      ;;

  -)  break ;;           # STDIN,  end of user options

  --) shift; break ;;    # end of user options
  -*) Usage "Unknown option \"$1\"" ;;
  *)  break ;;           # end of user options

  esac
  shift   # next option
done

# Two filename arguments are needed
[ $# -ne 2 ] && Usage "No enough arguments"

in="$1"
out="$2"

tmp="${TMPDIR:-/tmp}/$PROGNAME.$$"
mkdir $tmp
if [ $? -ne 0 ]; then
  echo >&2 "$PROGNAME: Failed to create directory \"$tmp\" -- ABORTING"
  exit 1
fi
trap "rm -rf $tmp" 0
trap "exit 2" 1 2 3 15

# ------------------------------

# Read input image, once only as it may be pipeline
magick "$in" -alpha on +repage "$tmp/in.mpc"

# FUTURE: search for multiple holes and deal with each one hole at a time.

# Extract the edge pixels around any transparent hole and trim smaller
#
# also get image page geometry and actual image size
offset=`magick "$tmp/in.mpc" \
          -channel A -morphology EdgeIn Disk:"$thickness.4" \
          $trim -print '%X%Y' +repage "$tmp/edges.mpc"`

size=`magick "$tmp/edges.mpc" -format '%wx%h' info:`

#magick display "$tmp/edges.mpc"

# Fast shepards Method to diffuse colors (good for image up to 256 pixels)
magick "$tmp/edges.mpc" \
        \( +clone -resize 50% \) \
        \( +clone -resize 50% \) \
        \( +clone -resize 50% \) \
        \( +clone -resize 50% \) \
        \( +clone -resize 50% \) \
        \( +clone -resize 50% \) \
        \( +clone -resize 50% \) \
        -layers RemoveDups -filter Gaussian -resize "$size!" \
        -background None -compose DstOver -layers merge \
        -alpha opaque "$tmp/diffuse.mpc"

#magick display "$tmp/diffuse.mpc"

# Compose the fill colors under the hole and output the result
magick "$tmp/in.mpc" "$tmp/diffuse.mpc" \
        -compose DstOver -geometry "$offset" -composite \
        -alpha off "$out"