A simple bash script to generate iOS icons

generate-icons.gh

#!/bin/bash

# Requirements
#  - bc - for some math
#  - convert - from ImageMagick (or any alternative that provides `convert` util with -resize param)
#  - optipng - to optimize the output from convert
#  - jq - to read Contents.json if no GEN_SIZES

# Usage:
# ------
#
# generate-icons.sh input.png
#
# Will generate:
# ./AppIcon.appiconset/Icon-App-20x20@2x.png
# ./AppIcon.appiconset/Icon-App-20x20@3x.png
# ./AppIcon.appiconset/Icon-App-29x29@1x.png
# ./AppIcon.appiconset/Icon-App-29x29@2x.png
# ./AppIcon.appiconset/Icon-App-29x29@3x.png
# ./AppIcon.appiconset/Icon-App-40x40@2x.png
# ./AppIcon.appiconset/Icon-App-40x40@3x.png
# ./AppIcon.appiconset/Icon-App-60x60@2x.png
# ./AppIcon.appiconset/Icon-App-60x60@4x.png
# ./AppIcon.appiconset/Icon-App-1024x1024@1x.png
#
# ###
#
# GEN_SIZES=512:1024 generate-icons.sh input.png .
#
# Will generate:
# ./Icon-App-512x512@1x.png
# ./Icon-App-1024x1024@1x.png
#
# Env variables:
# --------------
#
# ICONSET_DIR=AppIcon.appiconset
# PREFIX=Icon-App-
# GEN_SIZES=20@2,3:29@1,2,3:40@2,3:60@2,3:1024
#
# Generated sizes format: SIDE[@SCALE[,SCALE]...][:SIDE]...
# -----------------------
#
# 20:30:40          = 20x20@1x 30x30@1x 40x40@1x
# 20@1:30@2:40@3    = 20x20@1x 30x30@2x 40x40@3x
# 20@1,2:83.5@1,2,3 = 20x20@1x 20x20@2x 83.5x83.5@1x 83.5x83.5@2x 83.5x83.5@3x
#
# If there's no GEN_SIZES env var but a file ./AppIcon.appiconset/Contents.json
# then it will be read to use the filenames, sizes and scales from it.
#
# If a filename is missing in the json (aka null) it will be generated from the
# param.

IMAGE="$1"
ICONSET_DIR="${2:-AppIcon.appiconset}"
PREFIX="${PREFIX:-Icon-App-}"

FILENAMES=""
SIZES=""
SCALES=""
if [[ -z "$GEN_SIZES" ]]; then
  if [[ -f "$ICONSET_DIR/Contents.json" ]]; then
    FILENAMES=$(cat "$ICONSET_DIR/Contents.json" | jq -r ".images[].filename")
    SIZES=$(cat "$ICONSET_DIR/Contents.json" | jq -r ".images[].size")
    SCALES=$(cat "$ICONSET_DIR/Contents.json" | jq -r ".images[].scale")
  else
    GEN_SIZES="20@2,3:29@1,2,3:40@2,3:60@2,3:1024"
  fi
fi

if [[ -n "$GEN_SIZES" ]]; then
  for size in $(echo "$GEN_SIZES" | tr ":" "\n"); do
    side=$(echo "$size" | cut -d "@" -f 1)
    scales=$(echo "$size" | cut -d "@" -s -f 2)
    scales=${scales:-1}
    for scale in $(echo "$scales" | tr "," "\n"); do
      FILENAMES="$FILENAMES${PREFIX}${side}x${side}@${scale}x.png:"
      SIZES="$SIZES${side}x${side}:"
      SCALES="$SCALES${scale}x:"
    done
  done
  FILENAMES=$(echo "${FILENAMES%?}" | tr ":" "\n")
  SIZES=$(echo "${SIZES%?}" | tr ":" "\n")
  SCALES=$(echo "${SCALES%?}" | tr ":" "\n")
fi

FILENAMES=($(echo "$FILENAMES"))
SIZES=($(echo "$SIZES"))
SCALES=($(echo "$SCALES"))

for i in $(seq 1 ${#FILENAMES[@]}); do
  filename="${FILENAMES[$i-1]}"
  size=$(echo "${SIZES[$i-1]}" | cut -d 'x' -f 1)
  scale="${SCALES[$i-1]%?}"

  if [[ "$filename" == "null" ]]; then
    filename="${PREFIX}${size}x${size}@${scale}x.png"
  fi

  echo "$filename"

  scaled_size=$(echo "($scale * $size) / 1" | bc)

  convert "$IMAGE" -resize "${scaled_size}x${scaled_size}" "${ICONSET_DIR}/${filename}"
  optipng -quiet "${ICONSET_DIR}/${filename}"
done