diff --git a/common/src/play_clj/core.clj b/common/src/play_clj/core.clj
index 5c8cda3..b224778 100644
--- a/common/src/play_clj/core.clj
+++ b/common/src/play_clj/core.clj
@@ -37,7 +37,16 @@
         (swap! screen assoc
                :renderer (create-renderer renderer)
                :camera (create-camera camera)
-               :total-time 0)
+               :total-time 0
+               :entities []
+               :add-entity (fn [entity]
+                             (->> entity
+                                  (conj (:entities @screen))
+                                  (swap! screen assoc :entities)))
+               :del-entity (fn [entity]
+                             (->> (:entities @screen)
+                                  (remove #(= % entity))
+                                  (swap! screen assoc :entities))))
         (on-show @screen))
       (render [delta-time]
         (swap! screen assoc :total-time (+ (:total-time @screen) delta-time))
@@ -52,6 +61,14 @@
   [name & {:keys [] :as options}]
   `(def ~name (defscreen* ~options)))
 
+(defn add-entity!
+  [{:keys [add-entity]} e]
+  (add-entity e))
+
+(defn remove-entity!
+  [{:keys [del-entity]} e]
+  (del-entity e))
+
 (defn set-screen!
   [^Game game ^Screen screen]
   (.setScreen game screen))
diff --git a/common/src/play_clj/render.clj b/common/src/play_clj/render.clj
index 976e858..c3af4c8 100644
--- a/common/src/play_clj/render.clj
+++ b/common/src/play_clj/render.clj
@@ -49,7 +49,7 @@
 
 ; draw entities
 
-(defmulti sprite-batch (fn [screen] (class (:renderer screen))) :default nil)
+(defmulti sprite-batch #(-> % :renderer class) :default nil)
 
 (defmethod sprite-batch nil [screen]
   (SpriteBatch.))
@@ -58,10 +58,13 @@
   (.getSpriteBatch (:renderer screen)))
 
 (defn draw-entities!
-  [screen entities]
-  (let [batch (sprite-batch screen)]
-    (.begin batch)
-    (doseq [{:keys [image x y width height]} entities]
-      (when (and image x y width height)
-        (.draw batch image x y width height)))
-    (.end batch)))
+  ([screen]
+    (draw-entities! screen (-> screen :entities)))
+  ([screen entities]
+    (let [batch (sprite-batch screen)]
+      (.begin batch)
+      (doseq [{:keys [image x y width height]} entities]
+        (when (and image x y width height)
+          (.draw batch image x y width height)))
+      (.end batch)
+      batch)))