samples: document ways of using prefix

CHANGELOG.md

@@ -10,6 +10,7 @@ Docs:
 * Documented the n-sided-ness of polygons and stars
 * svg: document rasterization on mask (#192)
 * Document how to run the code (#186)
+* Document some ways of using `prefix` in `save_png` (#268)
 
 Chores:
 * Bumped deps: Pango et al. to 3.3.6, Cairo to 1.16.4, Nokogiri to 1.10.3, Highline to 2.0.2

samples/saves/_save_filenames.rb

@@ -0,0 +1,24 @@
+require 'squib'
+
+# This demonstrates the many ways you can save file to save_png and the like
+Squib::Deck.new(width: 50, height: 50, cards: 2) do
+  background color: :white
+  text str: (0..16).to_a, font: 'Arial Bold 12'
+
+  # three digits, e.g. save_three_digits_000.png
+  save_png prefix: 'save_three_digits_', count_format: '%03d'
+
+  # foo_0.png
+  # bar_1.png
+  save_png prefix: ['foo_', 'bar_'], count_format: '%01d'
+
+  # foo.png
+  # bar.png
+  save_png prefix: ['foo', 'bar'], count_format: ''
+
+  # thief.png
+  # thug.png
+  data = csv data: "filename\nthief\nthug"
+  save_png prefix: data.filename, count_format: ''
+
+end