Blank window has opened when execute sample code.

[teslur]

When I execute sample code that is written in Usage section of README.md, blank window has opened.

Environment

$ uname -a
Darwin xxxxMacBook-Pro.local 18.5.0 Darwin Kernel Version 18.5.0: Mon Mar 11 20:40:32 PDT 2019; root:xnu-4903.251.3~3/RELEASE_X86_64 x86_64

$ ruby --version
ruby 2.6.2p47 (2019-03-13 revision 67232) [x86_64-darwin18]

Gemfile, Gemfile.lock and executed sample code

$ cat Gemfile
source "https://rubygems.org"

gem 'charty'
gem 'numo-narray'
gem 'matplotlib'

$ cat Gemfile.lock
GEM
  remote: https://rubygems.org/
  specs:
    charty (0.2.1)
      red-colors
    matplotlib (1.1.0)
      pycall (>= 1.0.0)
    numo-narray (0.9.1.6)
    pycall (1.3.0)
    red-colors (0.1.1)

PLATFORMS
  ruby

DEPENDENCIES
  charty
  matplotlib
  numo-narray

BUNDLED WITH
   1.17.2

$ cat sample_1.rb
require 'bundler/setup'
require 'charty'

charty = Charty::Plotter.new(:pyplot)

bar = charty.bar do
  series [0,1,2,3,4], [10,40,20,90,70], label: "sample1"
  series [0,1,2,3,4], [90,80,70,60,50], label: "sample2"
  series [0,1,2,3,4,5,6,7,8], [50,60,20,30,10, 90, 0, 100, 50], label: "sample3"
  range x: 0..10, y: 1..100
  xlabel 'foo'
  ylabel 'bar'
  title 'bar plot'
end
bar.render("sample_images/bar_pyplot.png")

Result

• Blank window has opened.

• Following image has been saved as sample_images/bar_pyplot.png.
  

When I execute same code and Gemefile in following environment, the window shows graphs.

$ uname -a
Darwin xxxxMacBook-Pro.local 18.5.0 Darwin Kernel Version 18.5.0: Mon Mar 11 20:40:32 PDT 2019; root:xnu-4903.251.3~3/RELEASE_X86_64 x86_64

$ ruby --version
ruby 2.6.5p114 (2019-10-01 revision 67812) [x86_64-darwin18]

[mrkn]

@teslur Sorry for the response to be late.
Avoiding to open a blank window, you may need to explicitly specify agg backend in matplotlib.

I think inserting the following code before or after charty = Charty::Plotter.new(:pyplot) resolves this issue.

require "matplotlib"
Matplotlib.use(:agg)