Since there were no solutions submitted on the mailing list this week
I've included a solution of my own.
class DiamondSquare
def self.rando
rand() - 0.5
end
def self.go(times)
arrays = [[0.5]]
ratio = 2
times.times do
arrays.map! do |array|
insert_nils(array)
end
arrays = insert_arrays(arrays)
compute_from_diagonals(arrays) {|a, b, c, d| (a + b + c +
d)/4 + rando*ratio}
compute_from_adjacents(arrays) {|a, b, c, d| (a + b + c +
d)/4 + rando*ratio}
ratio *= 0.5
end
return arrays
end
def self.insert_arrays(arrays)
new_arrays = []
arrays.size.times do |i|
array = arrays[i]
new_arrays.push array, Array.new(array.size, 0.0)
end
return new_arrays
end
def self.insert_nils(array)
new_array = []
array.size.times do |i|
new_array.push(array[i], 0.0)
end
return new_array
end
def self.compute_from_adjacents(arrays)
n = arrays.size
n.times do |row|
n.times do |col|
next if (row + col) % 2 == 0
arrays[row][col] =
yield(arrays[(row-1)%n][col], arrays[row][(col-1)%n],
arrays[row][(col+1)%n], arrays[(row+1)%n][col])
end
end
end
def self.compute_from_diagonals(arrays)
n = arrays.size
n.times do |row|
next if row % 2 == 0
n.times do |col|
next if col % 2 == 0
arrays[row][col] =
yield(arrays[(row-1)%n][(col-1)%n], arrays[(row-1)%n][(col+1)%n],
arrays[(row+1)%n][(col-1)%n], arrays[(row+1)%n][(col+1)%n])
end
end
end
def self.print_arrays(arrays)
i = 0
arrays.each do |array|
print "%4d: " % i
array.each do |ele|
print '%1.3f ' % ele
end
i += 1
puts
end
puts '---------------------------------------'
end
end
I actually wrote it almost a year ago to generate the terrain for
[Dungeon Farmer][1]. It's kind of clunky, but it has its merits. Some
of the interesting things about this solution are that rather than
start with a full sized array it starts with a small array (very small
actually, 1x1) and inserts empty elements to be filled in before each
step. This causes the array to double in width and height at each
iteration.
The `compute_from_diagonals` and `compute_from_adjacents` methods
yield the four adjacent or diagonal cells so that you can easily
change the nature of the computation. The cells wrap around in a
toroidal manner to make it easy to compute the values on the edges.
It was fun to make and I hope you find it interesting!
[1]: http://code.google.com/p/strd6/wiki/DungeonFarmer
···
--
-Daniel
http://rubyquiz.strd6.com