add fire example

Author: monkstone

contributed/fire.rb

@@ -0,0 +1,73 @@
+# After original by Alex Young https://github.com/alexyoung/fire-p5r
+
+# Algorithm:
+# 1. Create an indexed palette of red, orange and yellows
+# 2. Loop:
+# 3.   Draw a random set of colours from the palette at the bottom of the screen
+# 4.   Loop through each pixel and average the colour index value around it
+# 5.   Reduce the average by a fire intensity factor
+
+# k9 --run fire.rb
+load_library :palette
+
+def settings
+  size 320, 240
+end
+
+def setup
+  sketch_title 'Fire'
+  frame_rate 30
+  @palette = Palette.create_palette
+  @fire = []
+  @scale = 8
+  @width = width / @scale
+  @height = height / @scale
+  @intensity = 2
+end
+
+def draw
+  background 0
+  update_fire
+end
+
+def update_fire
+  random_line @height - 1
+  (0..@height - 2).each do |y|
+    (0..@width).each do |x|
+      # Wrap
+      left = x.zero? ? fire_data(@width - 1, y) : fire_data(x - 1, y)
+      right = (x == @width - 1) ? fire_data(0, y) : fire_data(x + 1, y)
+      below = fire_data(x, y + 1)
+      # Get the average pixel value
+      average = (left.to_i + right.to_i + (below.to_i * 2)) / 4
+      # Fade the flames
+      average -= @intensity if average > @intensity
+      set_fire_data x, y, average
+      fill @palette[average]
+      stroke @palette[average]
+      rect x * @scale, (y + 1) * @scale, @scale, @scale
+    end
+  end
+end
+
+def fire_data(x, y)
+  @fire[offset(x, y)]
+end
+
+def set_fire_data(x, y, value)
+  @fire[offset(x, y)] = value.to_i
+end
+
+def random_offset
+  rand(0..@palette.size)
+end
+
+def random_line(y)
+  (0...@width).each do |x|
+    @fire[offset(x, y)] = random_offset
+  end
+end
+
+def offset(x, y)
+  (y * @width) + x
+end

contributed/library/palette/palette.rb

@@ -0,0 +1,29 @@
+# generates an array of color ints
+class Palette
+  include Processing::Proxy # needed to access 'color' and 'map1d'
+  attr_reader :palette
+
+  def initialize
+    @palette = make_palette
+  end
+
+  def make_palette
+    (0..256).map do |i|
+      # Create the bands of colour for the palette (256 is the maximum colour))
+      case i
+      when 0..64 # Range of reds
+        color(*[map1d(i, 0..64, 1..255), 0, 0])
+      when 64..128 # Range of orange
+        color(*[255, map1d(i, 64..128, 1..255), 0])
+      when 128..172 # range of yellow
+        color(*[255, 255, map1d(i, 128..172, 1..255)])
+      else
+        color(*[180, 0, 0])
+      end
+    end
+  end
+
+  def self.create_palette
+    Palette.new.palette
+  end
+end