diff --git a/game.scm b/game.scm
index 68283d7..4cd58e6 100644
--- a/game.scm
+++ b/game.scm
@@ -127,18 +127,13 @@
 
 (define (update-objects!)
   (set! *objects*
-        ;; Filter out the objects that are baked into the background
-        ;; and thus do not need to be rendered repeatedly.  Then,
-        ;; z-sort the list so we render in the correct order.
-        ;; Finally, convert positions to vec2s for more efficient
-        ;; rendering.
+        ;; z-sort the list so we render in the correct order.  Then
+        ;; convert tile positions to vec2s of pixel coordinates for
+        ;; more efficient rendering.
         (map (match-lambda
                ((type #(x y _) . properties)
-                (pk 'obj `(,type ,(vec2 (* x tile-width) (* y tile-height)) ,@properties))))
-             (sort (filter-map (match-lambda
-                                 (((or 'wall 'exit) . _) #f)
-                                 (desc desc))
-                               ($ (level-actor *level*) 'describe))
+                `(,type ,(vec2 (* x tile-width) (* y tile-height)) ,@properties)))
+             (sort ($ (level-actor *level*) 'describe)
                    (lambda (a b)
                      (match a
                        ((_ #(_ _ az) . _)
@@ -243,14 +238,9 @@
 (define (draw-exit pos)
   (draw-tile context tileset 27 (vec2-x pos) (vec2-y pos)))
 
-(define (draw-wall type pos)
+(define (draw-wall pos type)
   (let ((x (vec2-x pos))
         (y (vec2-y pos)))
-    (match type
-      ('brick
-       (draw-tile context tileset 22 x y))
-      (_
-       (draw-tile context tileset 2 x y)))
     (match type
       ('electron-head
        (draw-tile context tileset 4 x y))
@@ -258,7 +248,7 @@
        (draw-tile context tileset 5 x y))
       (_ #f))))
 
-(define (draw-block type pos)
+(define (draw-block pos type)
   (let ((x (vec2-x pos))
         (y (vec2-y pos)))
     (match type
@@ -287,11 +277,10 @@
   (match obj
     (#f #f)
     (('player pos) (draw-player pos))
-    ;; Wall and exit tiles are baked into the background layer.
-    (('exit pos) #t)
-    (('wall pos type) #t)
-    (('block pos type) (draw-block type pos))
-    (('clock-emitter pos) (draw-clock-emitter pos))
+    (('exit pos) #t) ; drawn via background
+    (('wall pos type) (draw-wall pos type))
+    (('block pos type) (draw-block pos type))
+    (('clock-emitter pos) #t) ; drawn via background
     (('floor-switch pos on?) (draw-floor-switch pos on?))
     (('gem pos) (draw-gem pos))
     (('gate pos open?) (draw-gate pos open?))))
diff --git a/modules/game/actors.scm b/modules/game/actors.scm
index 02b554d..48ad02f 100644
--- a/modules/game/actors.scm
+++ b/modules/game/actors.scm
@@ -12,6 +12,15 @@
             ^player
             ^level))
 
+;; The default wireworld rules.  Actors are free to use this or
+;; implement their own rule for themselves.
+(define (wireworld-next wire-state neighbors)
+  (match wire-state
+    (#f #f)
+    ('copper (if (<= 1 neighbors 2) 'electron-head 'copper))
+    ('electron-head 'electron-tail)
+    ('electron-tail 'copper)))
+
 (define* (^cell bcom #:optional val)
   (case-lambda
     (() val)
@@ -31,8 +40,8 @@
     (('enter obj grid-info) #f)
     (('exit obj grid-info) #f)
     (('wire-state) #f)
+    (('update-wire-state grid-info) #f)
     (('alive?) #t)
-    (('set-wire-state) #f)
     (('describe) `(exit ,position))
     (('collide other offset grid-info) #f)))
 
@@ -50,8 +59,13 @@
        ((or 'copper 'electron-head 'electron-tail)
         type)
        (_ #f)))
-    (('set-wire-state type)
-     (bcom (^wall bcom x y type)))
+    (('update-wire-state grid-info)
+     (match type
+       ((or 'copper 'electron-head 'electron-tail)
+        (let* ((neighbors ($ grid-info 'wireworld-neighbor-count x y))
+               (type (wireworld-next type neighbors)))
+          (bcom (^wall bcom x y type))))
+       (_ #f)))
     (('alive?) #t)
     (('describe) `(wall ,position ,type))
     (('collide other offset grid-info) #f)))
@@ -71,10 +85,15 @@
        ((or 'copper 'electron-head 'electron-tail)
         type)
        (_ #f)))
-    (('set-wire-state type)
-     (match ($ position)
-       (#(x y _)
-        (bcom (^block bcom x y type)))))
+    (('update-wire-state grid-info)
+     (match type
+       ((or 'copper 'electron-head 'electron-tail)
+        (match ($ position)
+          (#(x y z)
+           (let* ((neighbors ($ grid-info 'wireworld-neighbor-count x y))
+                  (type (wireworld-next type neighbors)))
+             (bcom (^block bcom x y type))))))
+       (_ #f)))
     (('alive?) #t)
     (('describe) `(block ,($ position) ,type))
     (('collide other offset grid-info)
@@ -96,7 +115,7 @@
     (('pushed?) ($ pushed?))))
 
 (define (^clock-emitter bcom x y interval)
-  (define timer (spawn ^cell 1))
+  (define timer (spawn ^cell 0))
   (define position (vector x y 0))
   (match-lambda*
     (('type) 'emitter)
@@ -113,6 +132,7 @@
          'electron-tail)
         (else
          'copper))))
+    (('update-wire-state grid-info) #f)
     (('alive?) #t)
     (('set-wire-state type) #f)
     (('describe) `(clock-emitter ,position))
@@ -129,18 +149,17 @@
      ($ on? #t))
     (('exit obj grid-info)
      (when (= (length ($ grid-info 'occupants x y)) 1)
-       (pk 'OFF)
-       ($ on? #f)
+        ($ on? #f)
        (match ($ grid-info 'occupants target-x target-y)
          (() (pk "no switch target!"))
          ((target . _)
           ($ target 'deactivate)))))
     (('wire-state) #f)
+    (('update-wire-state grid-info) #f)
     (('alive?) #t)
     (('describe) `(floor-switch ,position ,($ on?)))
     (('collide other offset grid-info)
-     (pk 'ON)
-     ($ on? #t)
+      ($ on? #t)
      (match ($ grid-info 'occupants target-x target-y)
        (() (pk "no switch target!"))
        ((target . _)
@@ -156,6 +175,7 @@
     (('enter obj grid-info) #f)
     (('exit obj grid-info) #f)
     (('wire-state) #f)
+    (('update-wire-state grid-info) #f)
     (('alive?) (not ($ picked-up?)))
     (('describe) `(gem ,position))
     (('collide other offset grid-info)
@@ -174,6 +194,7 @@
     (('activate) ($ open? #t))
     (('deactivate) ($ open? #f))
     (('wire-state) #f)
+    (('update-wire-state grid-info) #f)
     (('alive?) #t)
     (('open?) ($ open?))
     (('describe) `(gate ,position ,($ open?)))
@@ -205,6 +226,7 @@
     (('enter obj grid-info) #f)
     (('exit obj grid-info) #f)
     (('wire-state) #f)
+    (('update-wire-state grid-info) #f)
     (('alive?) #t)
     (('describe) `(player ,($ position)))
     (('collide other offset grid-info)
@@ -259,13 +281,60 @@
     (vector-set! grid (+ (* y width) x) val))
   (define grid (make-grid '()))
 
+  (define wire-grid (make-grid #f))
+  (define (refresh-wire-grid)
+    (for-each-coord
+     (lambda (x y)
+       (let ((obj-cell (grid-ref grid x y))
+             (wire-cell (grid-ref wire-grid x y)))
+         (match ($ obj-cell)
+           (() #f)
+           ;; TODO: Handle tiles with many occupants.  Might not be
+           ;; necessary in practice.
+           ((refr . _)
+            ($ wire-cell ($ refr 'wire-state))))))))
+  (define (wire-state-at x y)
+    ($ (grid-ref/wrap wire-grid x y)))
+  (define (neighbor-count x y)
+    (define (check x y)
+      (match (wire-state-at x y)
+        ('electron-head 1)
+        (_ 0)))
+    (+ (check (- x 1) (- y 1))
+       (check x (- y 1))
+       (check (+ x 1) (- y 1))
+       (check (- x 1) y)
+       (check (+ x 1) y)
+       (check (- x 1) (+ y 1))
+       (check x (+ y 1))
+       (check (+ x 1) (+ y 1))))
+  ;; flattened 3x3 grid of neighbor states. '_' used to mark the
+  ;; center.
+  (define (neighbor-grid x y)
+    (vector (wire-state-at (- x 1) (- y 1))
+            (wire-state-at x (- y 1))
+            (wire-state-at (+ x 1) (- y 1))
+
+            (wire-state-at (- x 1) y)
+            '_
+            (wire-state-at (+ x 1) y)
+
+            (wire-state-at (- x 1) (+ y 1))
+            (wire-state-at x (+ y 1))
+            (wire-state-at (+ x 1) (+ y 1))))
+
   ;; Read-only access to query the grid.
   (define (^grid-info bcom)
     (match-lambda*
       (('occupied? x y)
        (not (null? ($ (grid-ref grid x y)))))
       (('occupants x y)
-       ($ (grid-ref grid x y)))))
+       ($ (grid-ref grid x y)))
+      ;; How many electron heads around (x, y)?
+      (('wireworld-neighbor-count x y)
+       (neighbor-count x y))
+      (('wireworld-neighbor-grid x y)
+       (neighbor-grid x y))))
   (define grid-info (spawn ^grid-info))
 
   (define (delq item lst)
@@ -318,23 +387,6 @@
                            (collide other other-pos other-prev-pos)))
                        (lp rest))))))))))))
   (define (tick)
-    (define (neighbors x y)
-      (define (check x y)
-        (match ($ (grid-ref/wrap grid x y))
-          (() 0)
-          ;; TODO: Handle tiles with many occupants.
-          ((refr . _)
-           (match ($ refr 'wire-state)
-             ('electron-head 1)
-             (_ 0)))))
-      (+ (check (- x 1) (- y 1))
-         (check x (- y 1))
-         (check (+ x 1) (- y 1))
-         (check (+ x 1) y)
-         (check (+ x 1) (+ y 1))
-         (check x (+ y 1))
-         (check (- x 1) (+ y 1))
-         (check (- x 1) y)))
     ;; Tick each object and check for collisions.
     ($ objects
        (let lp ((objs ($ objects)))
@@ -352,30 +404,10 @@
                   (cons obj (lp rest))
                   (lp rest)))))))
     ;; Advance Wirewold simulation.
-    (for-each (match-lambda
-                ((refr . wire-state)
-                 ($ refr 'set-wire-state wire-state)))
-              (let y-loop ((y 0) (updates '()))
-                (if (< y height)
-                    (y-loop (1+ y)
-                            (let x-loop ((x 0) (updates updates))
-                              (if (< x width)
-                                  (match ($ (grid-ref grid x y))
-                                    (() (x-loop (1+ x) updates))
-                                    ;; TODO: Handle many occupants
-                                    ((refr . _)
-                                     (match ($ refr 'wire-state)
-                                       (#f (x-loop (1+ x) updates))
-                                       ('copper
-                                        (if (<= 1 (neighbors x y) 2)
-                                            (x-loop (1+ x) (cons `(,refr . electron-head) updates))
-                                            (x-loop (1+ x) updates)))
-                                       ('electron-head
-                                        (x-loop (1+ x) (cons `(,refr . electron-tail) updates)))
-                                       ('electron-tail
-                                        (x-loop (1+ x) (cons `(,refr . copper) updates))))))
-                                  updates)))
-                    updates))))
+    (refresh-wire-grid)
+    (for-each (lambda (obj)
+                ($ obj 'update-wire-state grid-info))
+              ($ objects)))
 
   (match-lambda*
     (('tick) (tick))
diff --git a/modules/game/levels/level-3.tmx b/modules/game/levels/level-3.tmx
index d3b3bc1..3ecf9a6 100644
--- a/modules/game/levels/level-3.tmx
+++ b/modules/game/levels/level-3.tmx
@@ -1,31 +1,40 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<map version="1.8" tiledversion="1.8.6" orientation="orthogonal" renderorder="right-down" width="20" height="15" tilewidth="16" tileheight="16" infinite="0" nextlayerid="3" nextobjectid="5">
+<map version="1.8" tiledversion="1.8.6" orientation="orthogonal" renderorder="right-down" width="20" height="15" tilewidth="16" tileheight="16" infinite="0" nextlayerid="3" nextobjectid="12">
  <tileset firstgid="1" source="tiles.tsx"/>
  <layer id="1" name="background" width="20" height="15">
   <data encoding="csv">
 23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,
-23,23,23,24,24,24,24,24,24,24,24,24,24,24,24,24,24,23,23,23,
-23,23,24,24,24,24,24,24,24,28,24,24,24,24,24,24,24,24,23,23,
-23,24,24,24,24,24,24,24,24,24,24,24,3,3,24,24,24,24,24,23,
-23,49,3,3,3,3,24,3,3,3,3,3,3,24,3,3,3,3,3,23,
-23,24,24,24,24,24,24,24,24,24,24,24,3,3,24,24,24,24,24,23,
-23,24,24,24,24,24,24,24,24,24,24,24,24,24,24,24,24,24,24,23,
-23,24,24,24,24,24,24,24,24,24,24,24,24,24,24,24,24,24,24,23,
-23,24,24,24,24,24,24,24,24,24,24,24,24,24,24,24,24,24,24,23,
-23,24,24,24,24,24,24,24,24,24,24,24,24,24,24,24,24,24,24,23,
-23,24,24,24,24,24,24,24,24,24,24,24,24,24,24,24,24,24,24,23,
-23,24,24,24,24,24,24,24,24,24,24,24,24,24,24,24,24,24,24,23,
-23,23,24,24,24,24,24,24,24,24,24,24,24,24,24,24,24,24,23,23,
-23,23,23,24,24,24,24,24,24,24,24,24,24,24,24,24,24,23,23,23,
+23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,
+23,23,24,24,24,24,24,24,24,24,24,24,24,24,23,23,23,23,23,23,
+23,24,24,24,24,24,24,24,24,24,24,24,24,24,24,23,24,24,24,23,
+23,49,3,3,3,24,3,3,3,3,3,3,24,24,24,23,24,24,24,23,
+23,24,24,24,24,24,24,24,24,24,24,24,24,3,24,23,24,24,24,23,
+23,24,24,24,24,24,49,3,3,3,3,3,24,24,24,24,24,24,24,23,
+23,24,24,24,24,24,24,24,24,24,24,24,24,24,24,23,24,24,24,23,
+23,24,24,24,24,24,24,24,24,24,24,24,24,24,24,23,24,28,24,23,
+23,24,24,24,24,24,24,24,24,24,24,24,24,24,23,23,24,24,24,23,
+23,24,24,24,24,24,24,24,24,24,24,24,24,24,23,23,24,24,24,23,
+23,23,24,24,24,24,24,24,24,24,24,24,24,23,23,23,23,23,23,23,
+23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,
+23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,
 23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,23,23
 </data>
  </layer>
  <objectgroup id="2" name="objects">
-  <object id="1" type="player-spawn" gid="1" x="128" y="144" width="16" height="16"/>
-  <object id="4" type="block" gid="4" x="96" y="80" width="16" height="16">
+  <object id="1" type="player-spawn" gid="1" x="80" y="144" width="16" height="16"/>
+  <object id="4" type="block" gid="4" x="80" y="128" width="16" height="16">
    <properties>
     <property name="kind" value="copper"/>
    </properties>
   </object>
+  <object id="7" type="floor-switch" gid="25" x="80" y="96" width="16" height="16">
+   <properties>
+    <property name="target-x" type="int" value="11"/>
+    <property name="target-y" type="int" value="7"/>
+   </properties>
+  </object>
+  <object id="8" type="electric-switch" gid="8" x="224" y="80" width="16" height="16"/>
+  <object id="9" type="gate" gid="46" x="240" y="96" width="16" height="16"/>
+  <object id="10" type="and-gate" gid="43" x="192" y="80" width="16" height="16"/>
  </objectgroup>
 </map>
diff --git a/scripts/compile-map.scm b/scripts/compile-map.scm
index a4d5cf4..d794d02 100644
--- a/scripts/compile-map.scm
+++ b/scripts/compile-map.scm
@@ -601,6 +601,9 @@ the default ORIENTATION value of 'orthogonal' is supported."
                                            (assq-ref properties 'target-y)))
                       ('gem (list x y obj:gem))
                       ('gate (list x y obj:gate))
+                      ;; TODO: Implement these
+                      ('and-gate (list x y obj:block:copper))
+                      ('electric-switch (list x y obj:wall:copper))
                       (_ (error "unsupported object type" type)))))
                 (object-layer-objects layer))))