Ruby Libgd

Library Status

Implemented	Implemented	Coming Next

Note: The images shown in Table 1, along with the code used to generate them, are available in the examples/ folder.

Native GD bindings for modern Ruby

What is ruby-libgd?

ruby-libgd is a modern native Ruby binding to the GD Graphics Library, providing Ruby with a fast, embeddable, server-side graphics engine.

It enables Ruby to generate images, charts, dashboards, GIS tiles, and scientific graphics without spawning external processes.

🐧Installation (Debian / Ubuntu /Dockerfile)

gem install ruby-libgd

System dependencies:

apt install -y libgd-dev pkg-config

---

🍎 macOS (Intel & Apple Silicon)

ruby-libgd is a native extension and depends on libgd, which must be installed via Homebrew.

Install libgd

brew install gd

Verify Homebrew’s install path:

brew --prefix gd

Typical values: Apple Silicon (M1 / M2 / M3): /opt/homebrew

Intel Macs: /usr/local

Install ruby-libgd

Apple Silicon (M1 / M2 / M3)

Homebrew installs libraries into /opt/homebrew, which Ruby’s native extension builder does not detect automatically.

Install using:

gem install ruby-libgd -- --with-gd-dir=/opt/homebrew

Intel macOS

gem install ruby-libgd

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📚 Documentation

• 🇬🇧 English: https://ggerman.github.io/ruby-libgd/en/
• 🇯🇵 日本語: https://ggerman.github.io/ruby-libgd/jp/

---

Examples:

All runnable examples live in:

examples/ basics/ image_processing/ charts/ images/

Each Ruby script in examples/ generates an image in examples/images/.

Links

GitHub: https://github.com/ggerman/ruby-libgd
RubyGems: https://rubygems.org/gems/ruby-libgd
Article: https://rubystacknews.com/2026/01/05/ruby-can-create-images-again/

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Build & Runtime Environment

ruby-libgd is developed and tested against libgd 2.3.3 using a reproducible Docker environment.

This ensures that the native extension is compiled against a known, stable GD ABI and behaves consistently across systems.

Reference Dockerfile

FROM ruby:3.3

RUN apt update && apt -y upgrade
RUN apt install -y \
  libgd-dev \
  libgd3 \
  libgd-tools \
  pkg-config \
  ruby-dev \
  build-essential \
  valgrind

RUN printf "prefix=/usr\n\
exec_prefix=\${prefix}\n\
libdir=\${exec_prefix}/lib/x86_64-linux-gnu\n\
includedir=\${prefix}/include\n\
\n\
Name: gd\n\
Description: GD Graphics Library\n\
Version: 2.3\n\
Libs: -L\${libdir} -lgd\n\
Cflags: -I\${includedir}\n" \
> /usr/lib/x86_64-linux-gnu/pkgconfig/gd.pc

ENV PKG_CONFIG_PATH=/usr/lib/x86_64-linux-gnu/pkgconfig

WORKDIR /app

COPY Gemfile Gemfile.lock ./
RUN bundle install

# Enforce dependency lockfile reproducibility
RUN bundle config --global frozen 1

COPY . .

Why this matters

ruby-libgd is a native C extension. The exact libgd version and build flags directly affect:

• Alpha blending

• Color accuracy

• Filter behavior

• Memory safety

Using a pinned, containerized build environment guarantees that:

• The extension is compiled against libgd 2.3.x

• pkg-config resolves the correct headers and linker flags

• CI, contributors, and users see identical behavior

This is especially important for GIS, map tiles, and image pipelines where pixel-level consistency matters.

Example:

require "gd"

WIDTH  = 800
HEIGHT = 400

img = GD::Image.new(WIDTH, HEIGHT)

# ----------------------------
# Pastel palette
# ----------------------------
bg_top    = [244, 240, 255]   # lavender
bg_bottom = [230, 248, 255]   # light sky

accent1 = [255, 140, 180]    # pastel pink
accent2 = [120, 200, 255]    # pastel blue
text_main = [60, 70, 120]    # deep indigo
shadow = [180, 190, 220]

# ----------------------------
# Soft gradient background
# ----------------------------
(0...HEIGHT).each do |y|
  t = y.to_f / (HEIGHT - 1)

  r = (bg_top[0] + (bg_bottom[0] - bg_top[0]) * t).to_i
  g = (bg_top[1] + (bg_bottom[1] - bg_top[1]) * t).to_i
  b = (bg_top[2] + (bg_bottom[2] - bg_top[2]) * t).to_i

  img.line(0, y, WIDTH - 1, y, [r, g, b])
end

# ----------------------------
# Floating pastel blobs
# ----------------------------
img.filled_circle(120, 100, 80, accent2)
img.filled_circle(680, 280, 100, accent1)
img.filled_circle(700, 80, 50, [200, 230, 255])

# ----------------------------
# Text
# ----------------------------
font = "/usr/share/fonts/truetype/dejavu/DejaVuSans.ttf"
title_size = 52
subtitle_size = 20

title = "RubyStackNews"
subtitle = "The pulse of the Ruby ecosystem"

# Manual centering
title_x = 80
title_y = 190

# Soft shadow
img.text(title, {
  x: title_x + 2,
  y: title_y + 2,
  size: title_size,
  color: shadow,
  font: font
})

# Main title
img.text(title, {
  x: title_x,
  y: title_y,
  size: title_size,
  color: text_main,
  font: font
})

# Subtitle
img.text(subtitle, {
  x: title_x,
  y: title_y + 45,
  size: subtitle_size,
  color: [100,110,160],
  font: font
})

# ----------------------------
# Call-to-action pill
# ----------------------------
pill_x = 80
pill_y = 260
pill_w = 260
pill_h = 44

img.filled_rectangle(pill_x, pill_y, pill_x + pill_w, pill_y + pill_h, [255,255,255])
img.rectangle(pill_x, pill_y, pill_x + pill_w, pill_y + pill_h, accent2, thickness: 2)

img.text("rubystacknews.com", {
  x: pill_x + 22,
  y: pill_y + 30,
  size: 20,
  color: text_main,
  font: font
})

# ----------------------------
# Save
# ----------------------------
img.save("images/rubystacknews-banner.png")
puts "Saved images/rubystacknews-banner.png"

License

MIT License. Copyright (c) 2025 Germán Alberto Giménez Silva.