initial commit

src/world/Collision.lua

@@ -0,0 +1,75 @@
+-- Movement permission checks: tile passability (from generated collision
+-- data), map bounds, and entity occupancy.
+
+local Collision = {}
+
+local DELTA = { up = { 0, -1 }, down = { 0, 1 }, left = { -1, 0 }, right = { 1, 0 } }
+Collision.DELTA = DELTA
+
+function Collision.target(cx, cy, dir)
+  local d = DELTA[dir]
+  return cx + d[1], cy + d[2]
+end
+
+-- entities: array of anything with cellX/cellY (and optional targetX/targetY
+-- while mid-step, so nobody walks into a cell being entered).
+function Collision.occupied(entities, cx, cy, ignore)
+  for _, e in ipairs(entities) do
+    if e ~= ignore then
+      if (e.cellX == cx and e.cellY == cy) or
+         (e.targetX == cx and e.targetY == cy) then
+        return e
+      end
+    end
+  end
+  return nil
+end
+
+-- Tile-pair (elevation) collisions: certain tile pairs can't be crossed
+-- in a given tileset (cave/forest ledges).  data set via Collision.load.
+local tilePairs = nil
+
+function Collision.load(data)
+  tilePairs = data.field and data.field.tilePairs or { land = {}, water = {} }
+end
+
+local function pairBlocked(map, mover, sx, sy, tx, ty)
+  if not tilePairs then return false end
+  local list = mover.surfing and tilePairs.water or tilePairs.land
+  if not list or #list == 0 then return false end
+  local tileset = map.def.tileset
+  local a = map:cellTile(sx, sy)
+  local b = map:cellTile(tx, ty)
+  for _, p in ipairs(list) do
+    if p.tileset == tileset
+       and ((p.a == a and p.b == b) or (p.a == b and p.b == a)) then
+      return true
+    end
+  end
+  return false
+end
+
+-- Returns true when the mover may step from (cx,cy) toward dir.
+-- Out-of-bounds is blocked here; the OverworldController handles map
+-- connections and edge warps before asking.
+function Collision.canMove(map, entities, mover, dir)
+  local tx, ty = Collision.target(mover.cellX, mover.cellY, dir)
+  if not map:inBounds(tx, ty) then
+    return false, "bounds"
+  end
+  if not map:isWalkableCell(tx, ty) then
+    -- surfers may ride water cells
+    if not (mover.surfing and map:isWaterCell(tx, ty)) then
+      return false, "tile"
+    end
+  end
+  if pairBlocked(map, mover, mover.cellX, mover.cellY, tx, ty) then
+    return false, "tile"
+  end
+  if Collision.occupied(entities, tx, ty, mover) then
+    return false, "entity"
+  end
+  return true
+end
+
+return Collision