feat(mapgen): add cellular-automata and drunkard-walk generators

src/gen/cellular.lua

@@ -0,0 +1,70 @@
+-- Cellular-automata caves. Seed the interior with random walls, then relax with
+-- the classic 4-5 rule so blobs of open space and rock emerge. Connectivity is
+-- enforced afterwards by the dungeon layer.
+
+local Map = require("map")
+local Tiles = require("tiles")
+
+local Cellular = {}
+
+local function wallNeighbours(grid, width, height, x, y)
+  local count = 0
+  for dy = -1, 1 do
+    for dx = -1, 1 do
+      if dx ~= 0 or dy ~= 0 then
+        local nx, ny = x + dx, y + dy
+        if nx < 1 or ny < 1 or nx > width or ny > height then
+          count = count + 1
+        elseif grid[(ny - 1) * width + nx] then
+          count = count + 1
+        end
+      end
+    end
+  end
+  return count
+end
+
+function Cellular.generate(width, height, rng, options)
+  options = options or {}
+  local fillChance = options.fillChance or 45
+  local steps = options.steps or 5
+  local grid = {}
+  for y = 1, height do
+    for x = 1, width do
+      local idx = (y - 1) * width + x
+      if x == 1 or y == 1 or x == width or y == height then
+        grid[idx] = true
+      else
+        grid[idx] = rng:range(1, 100) <= fillChance
+      end
+    end
+  end
+
+  for _ = 1, steps do
+    local nextGrid = {}
+    for y = 1, height do
+      for x = 1, width do
+        local idx = (y - 1) * width + x
+        local walls = wallNeighbours(grid, width, height, x, y)
+        if x == 1 or y == 1 or x == width or y == height then
+          nextGrid[idx] = true
+        else
+          nextGrid[idx] = walls >= 5
+        end
+      end
+    end
+    grid = nextGrid
+  end
+
+  local map = Map.new(width, height)
+  for y = 1, height do
+    for x = 1, width do
+      if not grid[(y - 1) * width + x] then
+        map:set(x, y, Tiles.FLOOR)
+      end
+    end
+  end
+  return map
+end
+
+return Cellular

src/gen/drunkard.lua

@@ -0,0 +1,37 @@
+-- Drunkard's walk: a set of random walkers stumble through the rock carving
+-- floor as they go, until a target fraction of the interior is open. Produces
+-- sinuous, organic corridors distinct from the blobby caves of the CA generator.
+
+local Map = require("map")
+local Tiles = require("tiles")
+
+local Drunkard = {}
+
+local STEPS = { { 1, 0 }, { -1, 0 }, { 0, 1 }, { 0, -1 } }
+
+function Drunkard.generate(width, height, rng, options)
+  options = options or {}
+  local coverage = options.coverage or 0.42
+  local target = math.floor((width - 2) * (height - 2) * coverage)
+  local map = Map.new(width, height)
+  local x, y = width // 2, height // 2
+  map:set(x, y, Tiles.FLOOR)
+  local carved = 1
+  local budget = width * height * 40
+
+  while carved < target and budget > 0 do
+    budget = budget - 1
+    local dir = STEPS[rng:range(1, 4)]
+    local nx, ny = x + dir[1], y + dir[2]
+    if nx >= 2 and ny >= 2 and nx <= width - 1 and ny <= height - 1 then
+      x, y = nx, ny
+      if map:get(x, y) ~= Tiles.FLOOR then
+        map:set(x, y, Tiles.FLOOR)
+        carved = carved + 1
+      end
+    end
+  end
+  return map
+end
+
+return Drunkard