#!/bin/bash
#
#  slideshow_morph [-r] images
#
# This program attempts to use the -remote capabilities of "animate" to
# generate a morphing slideshow on the fly.  That is while one picture is
# being displayed, the program will select and prepare the next morph or
# 'transition' to use.
#
# The point of this is that IM can take as much time as it likes to generate
# the next 'transtion animation'. When it is ready it can then
# magick animate the transition being displayed, leaving the magick display with the next
# image.
#
# The next image can be any image, randomly selected or otherwise.  The script
# does not need any fore-knowledge of the whole image sequence, only what the
# next image to be displayed will be.
#
# Note that all images given should be all the same size!
#
# See also the 'slideshow_next' script, that only does the transition
# to the next given image, then exits, until called again.
#
###
#
# FUTURE: some way of getting feedback from the "animate" or "display"
# programs when it has reached the end of the current "animation" would
# make determining when this wrapper script can proceed, a how lot easier.
#
###
#
# Anthony Thyssen     2008
#


#DEBUG=true
if [ "X$1" = 'X-r' ]; then
  randomize=true
  shift
fi

files=( "$@" )    # just save all the image filenames into an array

if [ ${#files} -le 1 ]; then
  echo >&2 "$0: 2 or more images needed to form a slideshow!"
fi

# Pick a image from that list as a start point
#
if [ "$randomize" ]; then
  prev_index=`expr $RANDOM \* ${#files} / 32768`
else
  prev_index=0
fi
prev_image="${files[$prev_index]}"


# Launch the animation sub-process
magick animate -loop 0 -delay 100 "$prev_image" &
animate_pid=$!


# Set up a temporary file for the transition animation with automatic
# cleanup. A MIFF file format is used as it is simplier and more exact (more
# colors) than the GIF file format.  GIF however could have been used.
#
umask 77
temp=`mktemp "${TMPDIR:-/tmp}/slideshow.XXXXXXXXXX.miff"` ||
  { echo >&2 "$PROGNAME: Unable to create temporary file"; exit 10;}
trap 'rm -f "$temp"' 0
trap "kill $animate_pid 2>/dev/null; exit 2" 1 2 3 15

# Loop forever
while :; do

  # pick next image
  if [ "$randomize" ]; then
    next_index=`expr $RANDOM \* ${#files} / 32768`
  else
    next_index=`expr $prev_index + 1 % ${#files}`
  fi
  [ $next_index -eq $prev_index ] && continue   # try again
  next_image="${files[$next_index]}"


  [ "$DEBUG" ] &&
    echo "morphing $prev_image ($prev_index) -> $next_image ($next_index)"

  # Do you complex image transition here
  # The final delay is minimum magick display time
  # The extra frame is to prevent a 'flash' of the first frame
  # just before the 'static' magick display is set.
  magick -delay 20 "$prev_image" "$next_image" -morph 10 \
          \( +clone -set delay 1000 \) +swap +delete \
          -loop 0 $temp

  #[ "$DEBUG" ] &&
  #  echo "sleeping what is left of the required 'display' time."
  #sleep 1

  # Has the animation been killed! if so exit
  kill -0 $animate_pid || exit 0

  [ "$DEBUG" ] &&
    echo "doing transition"
  magick animate -loop 0 -remote ephemeral:$temp &
  while [ -f $temp ]; do sleep .1; done  # wait for file to finish

  # Wait for transition time period to complete.
  # Must be longer than transition time, but shorter than overall time.
  #
  # The transition magick animate must not reach the final frame or a flash
  # of the first (original image) frame will become visible! (a bug)
  sleep 10

  # Has the animation been killed! if so exit
  kill -0 $animate_pid || exit 0

  # replace the animation with the new image and long 1 sec delay
  [ "$DEBUG" ] &&
    echo "replacing transition with static image"
  magick animate -loop 0 -delay 100 -remote "$next_image" &

  # Has the animation been killed! if so exit
  kill -0 $animate_pid || exit 0

  # At this point we can now take as long as needed
  # to generate a new transition!
  prev_index=$next_index
  prev_image="$next_image"

done