Spawn ghost gems where gems used to be.

modules/game/actors.scm

@@ -9,6 +9,7 @@
             ^floor-switch
             ^gate
             ^gem
+            ^ghost-gem
             ^and-gate
             ^xor-gate
             ^or-gate
@@ -268,6 +269,21 @@
      (when (eq? ($ other 'type) 'player)
        ($ picked-up? #t)))))
 
+(define (^ghost-gem bcom x y)
+  (define position (vector x y 1))
+  (match-lambda*
+    (('type) 'ghost-gem)
+    (('position) position)
+    (('tick grid-info) #f)
+    (('post-tick grid-info) #f)
+    (('enter obj grid-info) #f)
+    (('exit obj grid-info) #f)
+    (('wire-state grid-info) #f)
+    (('update-wire-state grid-info) #f)
+    (('alive?) #t)
+    (('describe) `(ghost-gem ,position))
+    (('collide other offset grid-info) #f)))
+
 (define (^gate bcom x y)
   (define position (vector x y 1))
   (define open? (spawn ^cell))
@@ -461,6 +477,7 @@
               ($ event '(bump)))))
        ('switch ($ event '(switch)))
        ('gem ($ event '(gem)))
+       ('ghost-gem #t)
        ('gate
         (unless ($ other 'open?)
           (reverse-move)