adding camera panning. nice.

desktop/src-common/advent/tween.clj

@@ -0,0 +1,53 @@
+(ns advent.tween)
+
+(defn ease-in-expo [power t start delta duration]
+  (let [pct-done (/ t duration)
+        pct-done (Math/pow pct-done power)]
+    (+ start
+       (* delta pct-done))))
+
+(def ease-linear (partial ease-in-expo 1.0))
+(def ease-in-quadratic (partial ease-in-expo 2.0))
+(def ease-in-cubic (partial ease-in-expo 3.0))
+(def ease-in-quartic (partial ease-in-expo 4.0))
+(def ease-in-quintic (partial ease-in-expo 5.0))
+(def ease-in-dectic (partial ease-in-expo 10.0))
+
+(defn ease-in-out-quadratic [t start delta duration]
+  (let [t (/ t (/ duration 2))]
+    (if (< t 1)
+      (+ (* (/ delta 2)
+            t t)
+         start)
+      (let [t (dec t)]
+        (+ (* (/ (- delta) 2)
+              (dec (* t (- t 2))))
+           start)))))
+
+(defn ease-in-out-quintic [t start delta duration]
+  (let [t (/ t (/ duration 2))]
+    (if (< t 1)
+      (+ (* (/ delta 2)
+            t t t t t)
+         start)
+      (let [t (- t 2)]
+        (+ (* (/ (- delta) 2)
+              (-  (* t t t t) 2))
+           start)))))
+
+(defn tween [id screen path start end duration & {:keys [finish ease]}]
+  (let [ease (or ease ease-linear)
+        finish (or finish identity)
+        start-time (or (:total-time screen) 0.0)
+        delta (- end start)]
+    (fn [e total-time]
+      (let [delta-time (- total-time start-time)
+            pct-done (min (/ delta-time duration) 1.0)
+            new-val (ease delta-time start delta duration)
+            e (assoc-in e path (if (= 1.0 pct-done)
+                                 end
+                                 new-val))]
+        
+        (if (= 1.0 pct-done)
+          (update-in (finish e) [:tweens] dissoc id)
+          e)))))