TIL: Add a custom rectangle to existing image with Ruby and RMagick

README.md

# Gemfile
gem 'rmagick'

require 'RMagick'

image = Magick::Image.read("before.png").first
gc = Magick::Draw.new
gc.stroke('green')
gc.stroke_width(5)
gc.fill('transparent')
gc.rectangle(upper_left_x, upper_left_y, lower_right_x, lower_right_y) ⇒ Object
gc.draw(image)
image.write("after.png")

• https://www.rubydoc.info/gems/rmagick/Magick
• https://rmagick.github.io/transparent.rb.html