Rays - A 2D drawing engine on OpenGL

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Rays is a hardware-accelerated 2D drawing engine for Ruby. It is built on OpenGL and exposes a retained-mode-friendly API: build Polygon, Polyline, Image, Shader, and Font objects, then paint them into an off-screen Image (or a window provided by Reflex) through a Painter.

It is the rendering layer used by Reflex, Processing, RubySketch, and Reight. Like the rest of the xord/* family, it is primarily developed for our own use, but it also works as a standalone drawing gem.

• Ruby 3.0.0 or later
• A C++ compiler with C++20 support
• Xot and Rucy (declared as runtime dependencies)
• Platform graphics backend:
  • macOS — AppKit, OpenGL, AVFoundation (bundled with the OS)
  • iOS — UIKit, OpenGL ES, AVFoundation (bundled with the OS)
  • Windows — GDI32, OpenGL32, GLEW (MINGW_PACKAGE_PREFIX-glew)
  • Linux — libsdl2-dev, libsdl2-ttf-dev, libglew-dev

The following third-party libraries are cloned from GitHub and statically linked while the native extension is being built, so you do not need to install them separately:

Add this line to your Gemfile:

gem 'rays'

Then install:

$ bundle install

Or install it directly:

$ gem install rays

require 'rays' automatically calls Rays.init! and registers Rays.fin! at exit. Set $RAYS_NOAUTOINIT = true before requiring if you want to manage the lifetime yourself.

Rays needs a current OpenGL context. When used through Reflex, the window creates and binds a context for you. To use Rays standalone for off-screen rendering, it allocates a hidden context automatically.

Rays::Painter is the immediate-mode drawing surface. Obtain one through Image#painter, then between painter.paint do |p| ... end (or begin_paint / end_paint) issue draw calls:

• Shapes — point, line, rect, ellipse, curve, bezier, triangle, quad, polygon
• Bitmaps & text — image, text
• State — fill, stroke, background, stroke_width, stroke_cap, stroke_join, blend_mode, clip, font, texture, shader
• Transforms — translate, scale, rotate, set_matrix
• Push / pop — push(:state, :matrix) / pop, or the block form push(fill: ..., stroke: ...) { ... }

stroke_cap, stroke_join, blend_mode, texcoord_mode, texcoord_wrap accept symbols (e.g. :round, :miter, :multiply).

• Rays.init! / Rays.fin! — explicit lifecycle (called automatically on require)
• Rays::Image.load(path) / Rays::Image#save(path) — image file I/O
• Rays.renderer_info — debug info about the current OpenGL context

require 'rays'

image = Rays::Image.new(200, 200)
image.paint do |p|
  p.background 0, 0, 0
  p.fill   1, 0.4, 0.1     # orange-ish
  p.stroke 1, 1, 1
  p.stroke_width 4

  p.rect 20, 20, 160, 160, round: 16
  p.ellipse 100, 100, 60, 60
end

image.save 'out.png'

require 'rays'

a = Rays::Polygon.rect(0, 0, 100, 100)
b = Rays::Polygon.ellipse(50, 50, 80, 80)

union        = a | b   # outer outline of both
difference   = a - b   # rectangle with circular bite
intersection = a & b   # lens-shaped overlap
xor          = a ^ b   # everything except the overlap

Rays::Image.new(140, 140).paint {|p| p.fill 1; p.polygon difference }.save 'diff.png'

(The C++ operator names map to Ruby's |, -, &, ^.)

require 'rays'

invert = Rays::Shader.new <<~GLSL
  uniform sampler2D texture;
  varying vec4 vTexCoord;
  void main() {
    vec4 c = texture2D(texture, vTexCoord.xy);
    gl_FragColor = vec4(1.0 - c.rgb, c.a);
  }
GLSL

src = Rays::Image.load('photo.png')
out = Rays::Image.new(src.width, src.height)
out.paint do |p|
  p.shader = invert
  p.image src
end
out.save 'photo-invert.png'

image.paint do |p|
  p.push(:state, :matrix, fill: [1, 0, 0]) do
    p.translate 50, 50
    p.rotate 30
    p.rect -20, -20, 40, 40
  end
  # fill, state, and matrix are restored here
end

$ rake vendor   # clone the external libraries into vendor/
$ rake lib      # build the native C++ library (librays)
$ rake ext      # build the Ruby C extension
$ rake test     # run the test suite
$ rake doc      # generate RDoc from C++ sources
$ rake          # default: builds the extension

The drawing tests render into off-screen images and compare pixels, so they require a working OpenGL context. The test_rays_init.rb test must run in its own process and is listed in TESTS_ALONE.

In the xord/all monorepo you can scope by module, e.g. rake rays test.

Rays is licensed under the MIT License. See the LICENSE file for details.

The third-party libraries listed above retain their own licenses (all MIT-compatible: MIT, ISC, Boost-1.0, dual-licensed MIT/Happy-Bunny for GLM, Unlicense for splines-lib).