jnx · November 9, 2017 19:20 · Jan 1, 2011
diff --git a/recursive-division.rb b/recursive-division.rb
@@ -0,0 +1,119 @@
+# --------------------------------------------------------------------
+# An implementation of the "Recursive Division" algorithm. This is a
+# kind of fractal maze algorithm, recursively dividing the maze into
+# smaller and smaller cells. This algorithm stops at the integer
+# boundary, but theoretically the algorithm could continue infinitely
+# to smaller and smaller scales.
+#
+# Note that this algorithm is implemented as a "wall adder", rather
+# than a "passage carver", so the meaning of the bits in each cell
+# is reversed: instead of the S bit (for instance) meaning "a passage
+# goes south", it means "there is a wall to the south".
+# --------------------------------------------------------------------
+
+# --------------------------------------------------------------------
+# 1. Allow the maze to be customized via command-line parameters
+# --------------------------------------------------------------------
+
+width  = (ARGV[0] || 10).to_i
+height = (ARGV[1] || width).to_i
+seed   = (ARGV[2] || rand(0xFFFF_FFFF)).to_i
+
+srand(seed)
+
+grid = Array.new(height) { Array.new(width, 0) }
+
+# --------------------------------------------------------------------
+# 2. Set up constants to aid with describing the passage directions
+# --------------------------------------------------------------------
+
+S, E = 1, 2
+HORIZONTAL, VERTICAL = 1, 2
+
+# --------------------------------------------------------------------
+# 3. Helper routines
+# --------------------------------------------------------------------
+
+def display_maze(grid)
+  print "\e[H" # move to upper-left
+  puts " " + "_" * (grid[0].length * 2 - 1)
+  grid.each_with_index do |row, y|
+    print "|"
+    row.each_with_index do |cell, x|
+      bottom = y+1 >= grid.length
+      south  = (cell & S != 0 || bottom)
+      south2 = (x+1 < grid[y].length && grid[y][x+1] & S != 0 || bottom)
+      east   = (cell & E != 0 || x+1 >= grid[y].length)
+
+      print(south ? "_" : " ")
+      print(east ? "|" : ((south && south2) ? "_" : " "))
+    end
+    puts
+  end
+end
+
+def choose_orientation(width, height)
+  if width < height
+    HORIZONTAL
+  elsif height < width
+    VERTICAL
+  else
+    rand(2) == 0 ? HORIZONTAL : VERTICAL
+  end
+end
+
+# --------------------------------------------------------------------
+# 4. The recursive-division algorithm itself
+# --------------------------------------------------------------------
+
+def divide(grid, x, y, width, height, orientation)
+  return if width < 2 || height < 2
+
+  display_maze(grid)
+  sleep 0.02
+
+  horizontal = orientation == HORIZONTAL
+
+  # where will the wall be drawn from?
+  wx = x + (horizontal ? 0 : rand(width-2))
+  wy = y + (horizontal ? rand(height-2) : 0)
+
+  # where will the passage through the wall exist?
+  px = wx + (horizontal ? rand(width) : 0)
+  py = wy + (horizontal ? 0 : rand(height))
+
+  # what direction will the wall be drawn?
+  dx = horizontal ? 1 : 0
+  dy = horizontal ? 0 : 1
+
+  # how long will the wall be?
+  length = horizontal ? width : height
+
+  # what direction is perpendicular to the wall?
+  dir = horizontal ? S : E
+
+  length.times do
+    grid[wy][wx] |= dir if wx != px || wy != py
+    wx += dx
+    wy += dy
+  end
+
+  nx, ny = x, y
+  w, h = horizontal ? [width, wy-y+1] : [wx-x+1, height]
+  divide(grid, nx, ny, w, h, choose_orientation(w, h))
+
+  nx, ny = horizontal ? [x, wy+1] : [wx+1, y]
+  w, h = horizontal ? [width, y+height-wy-1] : [x+width-wx-1, height]
+  divide(grid, nx, ny, w, h, choose_orientation(w, h))
+end
+
+print "\e[2J" # clear screen
+
+divide(grid, 0, 0, width, height, choose_orientation(width, height))
+display_maze(grid)
+
+# --------------------------------------------------------------------
+# 5. Show the parameters used to build this maze, for repeatability
+# --------------------------------------------------------------------
+
+puts "#{$0} #{width} #{height} #{seed}"
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