Trtl - Simple Ruby Turtle Graphics

Note

Trtl originally drew its graphics with Tk, which shipped with Ruby until Ruby 2.4 moved it out of the standard library and into a separate tk gem. That gem has to be compiled against a Tcl/Tk installation, which made Trtl a pain to set up, particularly on macOS. In 2026, Trtl was ported to LibUI, whose gem includes a precompiled native library for macOS, Windows and Linux, so on most systems gem install is all it takes.

Installation

gem install trtl

Description

Trtl is a simple 'turtle' system inspired by Python's turtle.py. It provides simple turtle drawing capabilities in Ruby, even if you're just at an IRB prompt. It draws using LibUI.

Usage

If Trtl detects you're in an IRB or Pry session, it'll automatically make turtle methods available directly at the prompt. For example:

$ irb
> require 'trtl'
> forward 100
# At this point, a window appears with the turtle

If you wish to use Trtl from a regular Ruby script, you have a few options. You can create a Trtl instance and use it directly:

require 'trtl'
t = Trtl.new
10.times { t.left(24); t.forward(30); t.ensure_drawn }
t.wait # keeps the window open until it's closed or Enter is pressed

You can use Trtl's run method to use it in a more interactive fashion:

Trtl.new.run { 10.times { left(24); forward(30); ensure_drawn }; wait }

Or you can include InteractiveTurtle and get a similar effect as if you were in IRB:

include InteractiveTurtle
10.times { left(24); forward(30) }
wait

Note: Using InteractiveTurtle makes drawing slower as it ensures all graphics are drawn after every action (as necessary for IRB use).

Commands

Only a small number of commands are currently implemented, but they're enough for the major actions:

• title(title_name)
• forward(distance) - aliased as fd
• back(distance) - aliased as bk and backward
• left(angle) - aliased as lt and turnleft
• right(angle) - aliased as rt and turnright
• pen_up - aliased as pu and up and penup
• pen_down - aliased as pd and down and pendown
• color(color_name) - aliased as pencolor. Accepts X11 color names ("darkolivegreen") or hex ("#1e90ff"), and returns the current color if called with no argument
• move(x, y) - aliased as goto, setpos and setposition
• home - returns to the center of the canvas, facing right
• position - aliased as pos
• circle(radius, extent = 360, steps = 360)
• dot(size) - draws a dot, defaults to a sensible size but you can supply if you want
• is_drawing?
• width(width_in_pixels)
• ensure_drawn - makes sure everything drawn so far is on screen (useful in loops in scripts)
• wait - keeps the window open until it's closed or Enter is pressed (needed at the end of scripts, not in IRB)

Examples

The examples in the examples folder should be reasonably illustrative. If you try any of them, try example4.rb - it renders an awesome looking tree.

Credits

• turtle.py for inspiration (in the 'Ruby needs this!' sense)
• Some of the examples taken from examples for an earlier Ruby turtle found at http://www.rubyquiz.com/quiz104.html

Copyright and License

Copyright (c) 2012-2026 Peter Cooper (other than minor parts of some samples.)

MIT licensed. See LICENSE.md