..Generate Dithered Gradient Animation

.gitignore

anim.gif

genanim

#!/bin/sh
set -eu

log() {
	echo "[genanim] $@"
}

require() {
	missing_bin=0

	for bin in "$@"; do
		if ! which "$bin" > /dev/null 2>&1; then
			missing_bin=1
			_error "Required: $bin"
		fi
	done

	if [ $missing_bin -ne 0 ]; then
		_fatal "$E_MISSING_APP" "One or more executables or apps are missing."
	fi
}

which magick > /dev/null 2>&1 || (echo "ImageMagick 7 required." >&2 && exit 16)

log "Starting animated GIF generation…"

TMPDIR=$(mktemp -d)
cleanup() {
	[ -n "${TMPDIR:-}" ] && [ -d "$TMPDIR" ] && rm -rf "$TMPDIR"
	log "Cleaned up temporary files."
}
trap cleanup EXIT INT

svg() {
	cat << SVG
<svg width="300" height="300" xmlns="http://www.w3.org/2000/svg">
  <defs>
    <linearGradient id="g" x1="0%" y1="0%" x2="100%" y2="100%">
      <stop offset="0%" stop-color="black"/>
      <stop offset="33.3333%" stop-color="white"/>
      <stop offset="66.6667%" stop-color="black"/>
      <stop offset="100%" stop-color="white"/>
    </linearGradient>
  </defs>
  <rect x="0" y="0" width="300" height="300" fill="url(#g)" />
</svg>
SVG
}

SIZE=240
FRAMES=48
FPS=12
DURATION=$(awk "BEGIN {print 100.0 / $FPS}")
OUTPUT=anim.gif

log "Temp folder: $TMPDIR"

log "Creating SVG file..."
svg > "$TMPDIR/grad.svg"

log "Creating diagonal gradient base…"
magick \
	-density 300 \
	"$TMPDIR/grad.svg" \
	-resize "$((SIZE * 3))x$((SIZE * 3))" \
	"$TMPDIR/gradient.png"

log "Applying ordered dithering (B/W)…"
magick "$TMPDIR/gradient.png" \
	-ordered-dither o8x8 \
	"$TMPDIR/dithered.png"

log "Generating $FRAMES frames…"
for i in $(seq 0 $((FRAMES - 1))); do
	OFFSET=$(awk "BEGIN {print int($i * ($SIZE * 2) / $FRAMES)}")
	magick "$TMPDIR/dithered.png" \
		-crop "${SIZE}x${SIZE}+$OFFSET+$OFFSET" +repage \
		"$TMPDIR/frame_$(printf "%02d" "$i").gif"
	log "Frame $i → offset: $OFFSET"
done

log "Assembling animation…"
magick -delay "$DURATION" -loop 0 "$TMPDIR"/frame_*.gif \
	-filter point -resize 960x960\! anim.gif

if which image_optim > /dev/null 2>&1; then
	log "Found image_optim."
	log "Optimizing with image_optim…"
	image_optim "$OUTPUT"
else
	log "No image_optim found. Skipped optimization."
fi

log "Done! Output: $OUTPUT"