Hard to believe, but I think fullscreen truly works, even through sleep.

desktop/src-common/advent/screens/scene.clj

@@ -955,7 +955,8 @@ void main()
                  (add-timer! screen k start time)))
   
   :on-render
-  (fn [{:keys [camera] :as screen} [entities]]
+  (fn [{:keys [camera ^FitViewport viewport] :as screen} [entities]]
+    (.apply viewport)
     (if (get-in entities [:closing? :value])
       
       (let [entities (utils/apply-tweens screen entities (:tweens entities))
@@ -1136,7 +1137,8 @@ void main()
       {:label (assoc (label "Demo version - DO NOT COPY" (color :white) ) :y 460 :x 5 :baseline 0 :opacity 0.5)}))
   
   :on-render
-  (fn [screen [entities]]
+  (fn [{:keys [^FitViewport viewport] :as screen} [entities]]
+    (.apply viewport)
     (render! screen [(:label entities)])
     entities)
 
@@ -1162,7 +1164,8 @@ void main()
        :fps (assoc (label "" (color :white) ) :x 5 :baseline 0 :opacity 0.1)}))
   
   :on-render
-  (fn [screen [entities]]
+  (fn [{:keys [viewport] :as screen} [entities]]
+    (.apply viewport)
     (let [entities (utils/apply-tweens screen entities (:tweens entities))]
       #_(label! (:fps entities) :set-text (str (game :fps))) 
       (render! screen [ (:inventory entities) (:close entities)])