feat(pathfinding): add a-star search and line of sight

src/los.lua

@@ -0,0 +1,33 @@
+-- Bresenham line of sight. A shot is clear when no cell strictly between the two
+-- endpoints blocks sight; the endpoints themselves are never treated as blockers
+-- so an actor can fire at something standing in a doorway.
+
+local Los = {}
+
+function Los.line(x0, y0, x1, y1)
+  local cells = {}
+  local dx = math.abs(x1 - x0)
+  local dy = math.abs(y1 - y0)
+  local sx = x0 < x1 and 1 or -1
+  local sy = y0 < y1 and 1 or -1
+  local err = dx - dy
+  local x, y = x0, y0
+  while true do
+    cells[#cells + 1] = { x = x, y = y }
+    if x == x1 and y == y1 then break end
+    local e2 = 2 * err
+    if e2 > -dy then err = err - dy; x = x + sx end
+    if e2 < dx then err = err + dx; y = y + sy end
+  end
+  return cells
+end
+
+function Los.clear(map, x0, y0, x1, y1)
+  local cells = Los.line(x0, y0, x1, y1)
+  for i = 2, #cells - 1 do
+    if map:blocksSight(cells[i].x, cells[i].y) then return false end
+  end
+  return true
+end
+
+return Los