#!/bin/sh
#
# convolve_image input_pixel_image  kernel_image  output_image
#
# Convert the kernel_image into convolution kernels (using the "image2kernel"
# script) and apply them to the given input_pixel_image which generally
# consists of multiple single white pixels on a black background.
#
# Effectivally this is a FAST multi-point composition technique.
#
# For example,
#   wget http://www.imagemagick.org/Usage/images/hand_point.gif
#   magick xc: -background black -gravity center -extend 60x60 pixel.gif
#
#   convolve_image pixel.gif hand_point.gif  convolved_pixel.gif
#
# Usally the convolution image is quite small.
#

input="$1"
kernel="$2"
output="$3"

# set directory for temporary files
tmp="${TMPDIR:-/tmp}"    # suggestions are dir="." or dir="/tmp"

[ -z "$tmp" ] && Error "Invalid TMPDIR setting"

# set up temp file
tmp=$tmp/$PROGNAME-$$
k=$tmp/kernel

trap "rm -rf $tmp; exit 0" 0
trap "rm -rf $tmp; exit 1" 1 2 3 15
mkdir $tmp ||
  Error "Unable to create tmp dir \"$tmp\""


IM_VERSION=`magick -list configure | \
     sed '/^LIB_VERSION_NUMBER /!d;
          s//,/;  s/,/,0/g;
          s/,0*\([0-9][0-9]\)/\1/g'`

if [ "$IM_VERSION" -lt '06070609' ]; then
  negate=-negate   # combine needs a negated alpha
fi

# Get kernel data from image
image2kernel $kernel $k.dat

# apply kernels to input image, and merge the results.
magick "$input" -alpha off \
        \( -clone 0 -morphology Convolve "@${k}_R.dat" \) \
        \( -clone 0 -morphology Convolve "@${k}_G.dat" \) \
        \( -clone 0 -morphology Convolve "@${k}_B.dat" \) \
        \( -clone 0 -morphology Convolve "@${k}_A.dat" $negate \) \
        -delete 0 -channel RGBA -combine "$output"

exit 0

# This should work and work faster, but fails mysteriously.
# I think it is showing up some bug in Morphology Convolve for Alpha channel
#

magick "$input" -alpha shape \
        -channel R -morphology Convolve "@${k}_R.dat"  \
        -channel G -morphology Convolve "@${k}_G.dat"  \
        -channel B -morphology Convolve "@${k}_B.dat"  \
        -channel A -morphology Convolve "@${k}_A.dat"  \
        "$output"