Generate "sunrise" gif for Slack emoji.

sunriser

#!/bin/bash

set -euo pipefail

trap "rm -f ,$$,*" EXIT

border=4
colors=256
delay=6
frames=30
rays=10

while (( $# > 0 ))
do
  case "$1" in
    -b)
      border="$2"
      shift 2
      ;;
    -c)
      colors="$2"
      shift 2
      ;;
    -d)
      delay="$2"
      shift 2
      ;;
    -f)
      frames="$2"
      shift 2
      ;;
    -r)
      rays="$2"
      shift 2
      ;;
    *)
      break
      ;;
  esac
done
if (( "$#" != 1 ))
then
  cat <<__END__
Usage: $0 [OPTIONS] FILE

FILE must have alpha channel, and its demension must be 128x128.

  -b N    Add N-px wide border around the base image.
  -c N    Set the preferred number of colors in the resulting image.
  -d N    Pause (N / 100) seconds before displaying the next frame.
  -f N    Generate N frames for the background animation.
  -r N    Generate N red rays for the background.
__END__
  exit 1
fi


infile="$1"

if (( $colors == 256 ))
then
  colors_args=()
else
  colors_args=(-colors $colors)
fi

magick "$infile" -background None -gravity Center -extent 128x128 \
  \( +clone -alpha Extract \
     -morphology Dilate Disk:$border -morphology Close Disk:$border \
     -threshold 50% \
     +duplicate \
     -compose CopyAlpha -composite \) \
  +swap \
  -compose SrcOver -composite \
  ,$$,infile-bordered.png

n="$frames"
for t in $(seq 0 $((n - 1)))
do
  magick -size 40x1000 gradient: -rotate 90 \
    +distort Polar 63 \
    -resize 128x128 \
    -function Sinusoid $rays,"%[fx:360*$t/$n]" \
    -threshold 50% \
    +level-colors red,white \
    ,$$,infile-bordered.png -composite \
    miff:-
done | magick - \
  +repage +dither +remap -layers OptimizeTransparency ${colors_args[@]:-} \
  -set delay $delay \
  ${infile/.*/}-sunrise-b$border-c$colors-d$delay-f$frames-r$rays.gif