feat: add Nodes.new, Nodes.isFallow and Noise.propagate

src/noise.lua

@@ -0,0 +1,74 @@
+-- Sound propagation. Unlike los.lua's straight sightline, a noisy action's
+-- racket bends around corners: it floods outward from its origin through
+-- open, walkable cells only, using the same four-directional adjacency
+-- astar.lua's own pathing already assumes (see its DIRS and game.lua's
+-- MONSTER_DIRS), and fades by exactly one point of loudness for every step
+-- the flood has to take to get there. A closed door or a solid wall stops
+-- it dead - nothing leaks through a wall diagonally the way it might with
+-- an eight-directional flood, so a noise never reaches anywhere a monster
+-- could not actually have walked to investigate it.
+--
+-- The flood itself has no idea what a monster or a player is; it is a pure
+-- function of the map, an origin and a starting loudness. game.lua's
+-- Game:emitNoise is what turns a resulting field into a dormant monster
+-- actually stirring (see stealth.lua's Stealth.hear).
+
+local Noise = {}
+
+local DIRS = { { 1, 0 }, { -1, 0 }, { 0, 1 }, { 0, -1 } }
+
+-- Loudness constants for the actions game.lua wires up to emitNoise, tuned
+-- so a whisper-quiet action (nothing currently that quiet) would decay
+-- within a couple of cells while a pick striking stone carries the length
+-- of a small floor.
+Noise.MELEE = 6
+Noise.RANGED = 6
+Noise.THROW = 5
+Noise.SPELL = 8
+Noise.DIG = 9
+
+-- Floods outward from (x, y) through walkable cells, returning a table
+-- keyed by map:index(nx, ny) -> the loudness still remaining once the sound
+-- has traveled there (loudness itself at the origin, decaying by one per
+-- step, never revisiting a cell at an intensity no better than one already
+-- recorded there). A cell the flood never reaches simply has no entry. The
+-- origin itself need not be walkable - a pick striking solid rock (see
+-- game.lua's Game:dig) is exactly as loud as one striking rubble - only the
+-- cells the flood actually spreads into have to be open for anything to
+-- ever stand in them and hear it.
+function Noise.propagate(map, x, y, loudness)
+  local field = {}
+  if loudness <= 0 or not map:inBounds(x, y) then return field end
+  local startIdx = map:index(x, y)
+  field[startIdx] = loudness
+  local queue = { { x = x, y = y, intensity = loudness } }
+  local head = 1
+  while head <= #queue do
+    local cur = queue[head]
+    head = head + 1
+    if cur.intensity > 0 then
+      local nextIntensity = cur.intensity - 1
+      for _, dir in ipairs(DIRS) do
+        local nx, ny = cur.x + dir[1], cur.y + dir[2]
+        if map:isWalkable(nx, ny) then
+          local idx = map:index(nx, ny)
+          if (field[idx] or -1) < nextIntensity then
+            field[idx] = nextIntensity
+            queue[#queue + 1] = { x = nx, y = ny, intensity = nextIntensity }
+          end
+        end
+      end
+    end
+  end
+  return field
+end
+
+-- Remaining loudness a previously computed field still carries at (x, y),
+-- or 0 for anywhere the flood never reached (including out of bounds, which
+-- map:index would otherwise happily compute an index for).
+function Noise.intensityAt(field, map, x, y)
+  if not map:inBounds(x, y) then return 0 end
+  return field[map:index(x, y)] or 0
+end
+
+return Noise