color group

docs/_posts/2019-03-03-Using-ColorGroup.md

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+---
+layout: post
+title:  "Using ColorGroup"
+date:   2019-03-03 00:50:08 +0000
+categories: vecmath update
+---
+
+# Example Usage
+
+ColorGroup can be initialized directly with and array of signed ints (corresponding to color integer), or indirectly from an array of "web string" as below.
+The order can be shuffled using `:shuffle!`. The colors are obtained by calling `:colors` on the group. 
+
+```ruby
+GEM_HOME = '/home/tux/.gem/ruby/2.6.0'
+require 'vecmath'
+
+PALETTE = %w[#0F4155 #158CA7 #D63826 #F5C03E #152A3B #7EC873 #4B3331].freeze
+
+
+  # create a java primitive array of signed int
+  #  @cols = web_array(PALETTE)
+  @group = ColorGroup.from_web_array(PALETTE)
+  @colors = @group.colors
+  stroke_cap SQUARE
+  stroke(0, 200)
+  @coloured = true
+
+
+def draw
+  arc_pattern
+  no_loop
+end
+
+def sep_index(idx, length)
+  (idx - (length - 1) * 0.5).abs.floor
+end
+
+def sep_color(idx, number)
+  @colors[sep_index(idx - 1, number + 1)]
+end
+
+def arc_pattern
+  circ_number = rand(4..10)
+  block_size = rand(30..70)
+  back_color = @coloured ? @group.last : 255
+  fill(back_color)
+  rect(0, 0, width, height)
+  half_block = block_size / 2
+  two_block = 2 * block_size
+  MathTool::grid(width + two_block, height + two_block, block_size, block_size) do |x, y|
+    push_matrix
+    translate x, y
+    rotate HALF_PI * rand(0..4)
+    circ_number.downto(0) do |i|
+      diam = two_block * i / (circ_number + 1)
+      ccolor = i < 2 || !coloured ? back_color : sep_color(i, circ_number)
+      fill ccolor
+      arc(-half_block, -half_block, diam, diam, 0, HALF_PI)
+      arc(half_block, half_block, diam, diam, PI, PI + HALF_PI)
+    end
+    pop_matrix
+  end
+end
+
+```