feat(light): add light-aware visibility

src/light.lua

@@ -0,0 +1,25 @@
+-- Visibility with light. The player sees out to their carried light radius via
+-- shadowcasting; on top of that, any static emitter the player can already see
+-- casts its own pool of light, so a lit room reveals itself the moment the
+-- player glimpses its brazier. Darkness is simply a smaller player radius.
+
+local Fov = require("fov")
+
+local Light = {}
+
+function Light.compute(map, originX, originY, radius, lights)
+  local visible = Fov.compute(map, originX, originY, radius)
+  if lights then
+    for _, emitter in ipairs(lights) do
+      if visible[map:index(emitter.x, emitter.y)] then
+        local pool = Fov.compute(map, emitter.x, emitter.y, emitter.radius)
+        for idx in pairs(pool) do
+          visible[idx] = true
+        end
+      end
+    end
+  end
+  return visible
+end
+
+return Light