diff --git a/src/play_clj/core_graphics.clj b/src/play_clj/core_graphics.clj
index 8c4b24b..53883f3 100644
--- a/src/play_clj/core_graphics.clj
+++ b/src/play_clj/core_graphics.clj
@@ -14,12 +14,12 @@
 
 (defmacro tiled-map!
   [screen k & options]
-  `(let [^BatchTiledMapRenderer object# (or (:renderer ~screen) ~screen)]
+  `(let [^BatchTiledMapRenderer object# (u/get-obj ~screen :renderer)]
      (u/call! ^TiledMap (.getMap object#) ~k ~@options)))
 
 (defn tiled-map-layers
   [screen]
-  (let [^BatchTiledMapRenderer renderer (or (:renderer screen) screen)
+  (let [^BatchTiledMapRenderer renderer (u/get-obj screen :renderer)
         ^MapLayers layers (-> renderer .getMap .getLayers)]
     (for [^long i (range (.getCount layers))]
       (.get layers i))))
@@ -67,7 +67,7 @@
 
 (defmacro orthogonal-tiled-map!
   [screen k & options]
-  `(let [^OrthogonalTiledMapRenderer object# (or (:renderer ~screen) ~screen)]
+  `(let [^OrthogonalTiledMapRenderer object# (u/get-obj ~screen :renderer)]
      (u/call! object# ~k ~@options)))
 
 (defn isometric-tiled-map*
@@ -81,7 +81,7 @@
 
 (defmacro isometric-tiled-map!
   [screen k & options]
-  `(let [^IsometricTiledMapRenderer object# (or (:renderer ~screen) ~screen)]
+  `(let [^IsometricTiledMapRenderer object# (u/get-obj ~screen :renderer)]
      (u/call! object# ~k ~@options)))
 
 (defn isometric-staggered-tiled-map*
@@ -98,7 +98,7 @@
 (defmacro isometric-staggered-tiled-map!
   [screen k & options]
   `(let [^IsometricStaggeredTiledMapRenderer object#
-         (or (:renderer ~screen) ~screen)]
+         (u/get-obj ~screen :renderer)]
      (u/call! object# ~k ~@options)))
 
 (defn hexagonal-tiled-map*
@@ -112,7 +112,7 @@
 
 (defmacro hexagonal-tiled-map!
   [screen k & options]
-  `(let [^HexagonalTiledMapRenderer object# (or (:renderer ~screen) ~screen)]
+  `(let [^HexagonalTiledMapRenderer object# (u/get-obj ~screen :renderer)]
      (u/call! object# ~k ~@options)))
 
 (defn stage*
@@ -125,7 +125,7 @@
 
 (defmacro stage!
   [screen k & options]
-  `(let [^Stage object# (or (:renderer ~screen) ~screen)]
+  `(let [^Stage object# (u/get-obj ~screen :renderer)]
      (u/call! object# ~k ~@options)))
 
 ; batch
@@ -209,7 +209,7 @@
 
 (defmacro orthographic!
   [screen k & options]
-  `(let [^OrthographicCamera object# (or (:camera ~screen) ~screen)]
+  `(let [^OrthographicCamera object# (u/get-obj ~screen :camera)]
      (u/call! object# ~k ~@options)))
 
 (defn perspective
@@ -223,12 +223,12 @@
 
 (defmacro perspective!
   [screen k & options]
-  `(let [^PerspectiveCamera object# (or (:camera ~screen) ~screen)]
+  `(let [^PerspectiveCamera object# (u/get-obj ~screen :camera)]
      (u/call! object# ~k ~@options)))
 
 (defn size!
   [screen width height]
-  (let [^OrthographicCamera camera (or (:camera screen) screen)]
+  (let [^OrthographicCamera camera (u/get-obj screen :camera)]
     (assert camera)
     (.setToOrtho camera false width height)))
 
@@ -242,21 +242,21 @@
 
 (defn x!
   [screen x]
-  (let [^Camera camera (or (:camera screen) screen)]
+  (let [^Camera camera (u/get-obj screen :camera)]
     (assert camera)
     (set! (. (. camera position) x) x)
     (.update camera)))
 
 (defn y!
   [screen y]
-  (let [^Camera camera (or (:camera screen) screen)]
+  (let [^Camera camera (u/get-obj screen :camera)]
     (assert camera)
     (set! (. (. camera position) y) y)
     (.update camera)))
 
 (defn z!
   [screen z]
-  (let [^Camera camera (or (:camera screen) screen)]
+  (let [^Camera camera (u/get-obj screen :camera)]
     (assert camera)
     (set! (. (. camera position) z) z)
     (.update camera)))
diff --git a/src/play_clj/g2d.clj b/src/play_clj/g2d.clj
index ed73821..6b633e4 100644
--- a/src/play_clj/g2d.clj
+++ b/src/play_clj/g2d.clj
@@ -14,19 +14,19 @@
       (string? arg)
       (-> ^String arg Texture. TextureRegion.)
       (map? arg)
-      (TextureRegion. ^TextureRegion (:object arg))
+      (TextureRegion. ^TextureRegion (u/get-obj arg :object))
       :else
       arg)))
 
 (defmacro texture
   [arg & options]
   `(let [entity# (texture* ~arg)]
-     (u/calls! ^TextureRegion (:object entity#) ~@options)
+     (u/calls! ^TextureRegion (u/get-obj entity# :object) ~@options)
      entity#))
 
 (defmacro texture!
   [entity k & options]
-  `(u/call! ^TextureRegion (:object ~entity) ~k ~@options))
+  `(u/call! ^TextureRegion (u/get-obj ~entity :object) ~k ~@options))
 
 (defmacro play-mode
   [key]
@@ -35,7 +35,7 @@
 (defn animation*
   [duration textures]
   (Animation. duration
-              (u/gdx-array (map :object textures))
+              (u/gdx-array (map #(u/get-obj % :object) textures))
               (play-mode :normal)))
 
 (defmacro animation
diff --git a/src/play_clj/g2d_physics.clj b/src/play_clj/g2d_physics.clj
index e8c95a4..4f4f8bd 100644
--- a/src/play_clj/g2d_physics.clj
+++ b/src/play_clj/g2d_physics.clj
@@ -22,7 +22,7 @@
 
 (defmacro box-2d!
   [screen k & options]
-  `(let [^World object# (or (:world ~screen) ~screen)]
+  `(let [^World object# (u/get-obj ~screen :world)]
      (u/call! object# ~k ~@options)))
 
 ; bodies
@@ -40,7 +40,7 @@
 
 (defmacro body!
   [entity k & options]
-  `(let [^Body object# (or (:body ~entity) ~entity)]
+  `(let [^Body object# (u/get-obj ~entity :body)]
      (u/call! object# ~k ~@options)))
 
 (defn create-body!*
@@ -180,7 +180,7 @@
 
 (defn first-contact
   ([screen]
-    (let [^Contact contact (or (:contact screen) screen)]
+    (let [^Contact contact (u/get-obj screen :contact)]
       (assert contact)
       (-> contact .getFixtureA .getBody)))
   ([screen entities]
@@ -188,7 +188,7 @@
 
 (defn second-contact
   ([screen]
-    (let [^Contact contact (or (:contact screen) screen)]
+    (let [^Contact contact (u/get-obj screen :contact)]
       (assert contact)
       (-> contact .getFixtureB .getBody)))
   ([screen entities]
diff --git a/src/play_clj/ui.clj b/src/play_clj/ui.clj
index 295dd51..b4e5399 100644
--- a/src/play_clj/ui.clj
+++ b/src/play_clj/ui.clj
@@ -149,12 +149,12 @@
 (defmacro check-box
   [text arg & options]
   `(let [entity# (check-box* ~text ~arg)]
-     (u/calls! ^CheckBox (:object entity#) ~@options)
+     (u/calls! ^CheckBox (u/get-obj entity# :object) ~@options)
      entity#))
 
 (defmacro check-box!
   [entity k & options]
-  `(u/call! ^Checkbox (:object ~entity) ~k ~@options))
+  `(u/call! ^Checkbox (u/get-obj ~entity :object) ~k ~@options))
 
 (defn dialog*
   [text arg]
@@ -163,12 +163,12 @@
 (defmacro dialog
   [text arg & options]
   `(let [entity# (dialog* ~text ~arg)]
-     (u/calls! ^Dialog (:object entity#) ~@options)
+     (u/calls! ^Dialog (u/get-obj entity# :object) ~@options)
      entity#))
 
 (defmacro dialog!
   [entity k & options]
-  `(u/call! ^Dialog (:object ~entity) ~k ~@options))
+  `(u/call! ^Dialog (u/get-obj ~entity :object) ~k ~@options))
 
 (defn horizontal*
   [children]
@@ -177,12 +177,12 @@
 (defmacro horizontal
   [children & options]
   `(let [entity# (horizontal* ~children)]
-     (u/calls! ^HorizontalGroup (:object entity#) ~@options)
+     (u/calls! ^HorizontalGroup (u/get-obj entity# :object) ~@options)
      entity#))
 
 (defmacro horizontal!
   [entity k & options]
-  `(u/call! ^HorizontalGroup (:object ~entity) ~k ~@options))
+  `(u/call! ^HorizontalGroup (u/get-obj ~entity :object) ~k ~@options))
 
 (defn image*
   [arg]
@@ -198,12 +198,12 @@
 (defmacro image
   [arg & options]
   `(let [entity# (image* ~arg)]
-     (u/calls! ^Image (:object entity#) ~@options)
+     (u/calls! ^Image (u/get-obj entity# :object) ~@options)
      entity#))
 
 (defmacro image!
   [entity k & options]
-  `(u/call! ^Image (:object ~entity) ~k ~@options))
+  `(u/call! ^Image (u/get-obj ~entity :object) ~k ~@options))
 
 (defn image-button*
   [arg]
@@ -212,12 +212,12 @@
 (defmacro image-button
   [arg & options]
   `(let [entity# (image-button* ~arg)]
-     (u/calls! ^ImageButton (:object entity#) ~@options)
+     (u/calls! ^ImageButton (u/get-obj entity# :object) ~@options)
      entity#))
 
 (defmacro image-button!
   [entity k & options]
-  `(u/call! ^ImageButton (:object ~entity) ~k ~@options))
+  `(u/call! ^ImageButton (u/get-obj ~entity :object) ~k ~@options))
 
 (defn image-text-button*
   [^String text arg]
@@ -226,12 +226,12 @@
 (defmacro image-text-button
   [text arg & options]
   `(let [entity# (image-text-button* ~text ~arg)]
-     (u/calls! ^ImageTextButton (:object entity#) ~@options)
+     (u/calls! ^ImageTextButton (u/get-obj entity# :object) ~@options)
      entity#))
 
 (defmacro image-text-button!
   [entity k & options]
-  `(u/call! ^ImageTextButton (:object ~entity) ~k ~@options))
+  `(u/call! ^ImageTextButton (u/get-obj ~entity :object) ~k ~@options))
 
 (defn label*
   [^String text arg]
@@ -243,26 +243,26 @@
 (defmacro label
   [text arg & options]
   `(let [entity# (label* ~text ~arg)]
-     (u/calls! ^Label (:object entity#) ~@options)
+     (u/calls! ^Label (u/get-obj entity# :object) ~@options)
      entity#))
 
 (defmacro label!
   [entity k & options]
-  `(u/call! ^Label (:object ~entity) ~k ~@options))
+  `(u/call! ^Label (u/get-obj ~entity :object) ~k ~@options))
 
 (defn scroll-pane*
   [child arg]
-  (u/create-entity (ScrollPane. (:object child) arg)))
+  (u/create-entity (ScrollPane. (u/get-obj child :object) arg)))
 
 (defmacro scroll-pane
   [child arg & options]
   `(let [entity# (scroll-pane* ~child ~arg)]
-     (u/calls! ^ScrollPane (:object entity#) ~@options)
+     (u/calls! ^ScrollPane (u/get-obj entity# :object) ~@options)
      entity#))
 
 (defmacro scroll-pane!
   [entity k & options]
-  `(u/call! ^ScrollPane (:object ~entity) ~k ~@options))
+  `(u/call! ^ScrollPane (u/get-obj ~entity :object) ~k ~@options))
 
 (defn select-box*
   [items arg]
@@ -271,12 +271,12 @@
 (defmacro select-box
   [items arg & options]
   `(let [entity# (select-box* ~items ~arg)]
-     (u/calls! ^SelectBox (:object entity#) ~@options)
+     (u/calls! ^SelectBox (u/get-obj entity# :object) ~@options)
      entity#))
 
 (defmacro select-box!
   [entity k & options]
-  `(u/call! ^SelectBox (:object ~entity) ~k ~@options))
+  `(u/call! ^SelectBox (u/get-obj ~entity :object) ~k ~@options))
 
 (defn slider*
   [{:keys [min max step vertical?]
@@ -288,12 +288,12 @@
 (defmacro slider
   [attrs arg & options]
   `(let [entity# (slider* ~attrs ~arg)]
-     (u/calls! ^Slider (:object entity#) ~@options)
+     (u/calls! ^Slider (u/get-obj entity# :object) ~@options)
      entity#))
 
 (defmacro slider!
   [entity k & options]
-  `(u/call! ^Slider (:object ~entity) ~k ~@options))
+  `(u/call! ^Slider (u/get-obj ~entity :object) ~k ~@options))
 
 (defn stack*
   [children]
@@ -302,12 +302,12 @@
 (defmacro stack
   [children & options]
   `(let [entity# (stack* ~children)]
-     (u/calls! ^Stack (:object entity#) ~@options)
+     (u/calls! ^Stack (u/get-obj entity# :object) ~@options)
      entity#))
 
 (defmacro stack!
   [entity k & options]
-  `(u/call! ^Stack (:object ~entity) ~k ~@options))
+  `(u/call! ^Stack (u/get-obj ~entity :object) ~k ~@options))
 
 (defn table*
   [children]
@@ -316,12 +316,12 @@
 (defmacro table
   [children & options]
   `(let [entity# (table* ~children)]
-     (u/calls! ^Table (:object entity#) ~@options)
+     (u/calls! ^Table (u/get-obj entity# :object) ~@options)
      entity#))
 
 (defmacro table!
   [entity k & options]
-  `(u/call! ^Table (:object ~entity) ~k ~@options))
+  `(u/call! ^Table (u/get-obj ~entity :object) ~k ~@options))
 
 (defn text-button*
   [^String text arg]
@@ -330,12 +330,12 @@
 (defmacro text-button
   [text arg & options]
   `(let [entity# (text-button* ~text ~arg)]
-     (u/calls! ^TextButton (:object entity#) ~@options)
+     (u/calls! ^TextButton (u/get-obj entity# :object) ~@options)
      entity#))
 
 (defmacro text-button!
   [entity k & options]
-  `(u/call! ^TextButton (:object ~entity) ~k ~@options))
+  `(u/call! ^TextButton (u/get-obj ~entity :object) ~k ~@options))
 
 (defn text-field*
   [^String text arg]
@@ -344,12 +344,12 @@
 (defmacro text-field
   [text arg & options]
   `(let [entity# (text-field* ~text ~arg)]
-     (u/calls! ^TextField (:object entity#) ~@options)
+     (u/calls! ^TextField (u/get-obj entity# :object) ~@options)
      entity#))
 
 (defmacro text-field!
   [entity k & options]
-  `(u/call! ^TextField (:object ~entity) ~k ~@options))
+  `(u/call! ^TextField (u/get-obj ~entity :object) ~k ~@options))
 
 (defn tree*
   [children arg]
@@ -358,12 +358,12 @@
 (defmacro tree
   [children arg & options]
   `(let [entity# (tree* ~children ~arg)]
-     (u/calls! ^Tree (:object entity#) ~@options)
+     (u/calls! ^Tree (u/get-obj entity# :object) ~@options)
      entity#))
 
 (defmacro tree!
   [entity k & options]
-  `(u/call! ^Tree (:object ~entity) ~k ~@options))
+  `(u/call! ^Tree (u/get-obj ~entity :object) ~k ~@options))
 
 (defn vertical*
   [children]
@@ -372,12 +372,12 @@
 (defmacro vertical
   [children & options]
   `(let [entity# (vertical* ~children)]
-     (u/calls! ^VerticalGroup (:object entity#) ~@options)
+     (u/calls! ^VerticalGroup (u/get-obj entity# :object) ~@options)
      entity#))
 
 (defmacro vertical!
   [entity k & options]
-  `(u/call! ^VerticalGroup (:object ~entity) ~k ~@options))
+  `(u/call! ^VerticalGroup (u/get-obj ~entity :object) ~k ~@options))
 
 (defn window*
   [children ^String title arg]
@@ -386,9 +386,9 @@
 (defmacro window
   [children title arg & options]
   `(let [entity# (window* ~children ~title ~arg)]
-     (u/calls! ^Window (:object entity#) ~@options)
+     (u/calls! ^Window (u/get-obj entity# :object) ~@options)
      entity#))
 
 (defmacro window!
   [entity k & options]
-  `(u/call! ^Window (:object ~entity) ~k ~@options))
+  `(u/call! ^Window (u/get-obj ~entity :object) ~k ~@options))
diff --git a/src/play_clj/utils.clj b/src/play_clj/utils.clj
index 3e56c7c..d827826 100644
--- a/src/play_clj/utils.clj
+++ b/src/play_clj/utils.clj
@@ -4,11 +4,18 @@
            [com.badlogic.gdx.scenes.scene2d Actor]
            [com.badlogic.gdx.utils Array ArrayMap]))
 
-; exceptions
+; misc
 
 (defn throw-key-not-found
   [k]
-  (throw (Exception. (str "The keyword " k " is not supported."))))
+  (throw (Exception. (str "The keyword " k " is not found."))))
+
+(defn get-obj
+  [obj k]
+  (if (map? obj)
+    (or (get obj k)
+        (throw-key-not-found k))
+    obj))
 
 ; converting keys