Added active flag to avoid transform of inactive deepzoom images.

lib/scatter.js

@@ -173,11 +173,16 @@ class Throwable {
         }
     }
 
+    _throwDeltaTime() {
+        let t = performance.now()
+        let dt = t - this.lastframe
+        this.lastframe = t
+        return dt
+    }
+
     animateThrow(time) {
         if (this.velocity != null) {
-            let t = performance.now()
-            let dt = t - this.lastframe
-            this.lastframe = t
+            let dt = this._throwDeltaTime()
             // console.log("animateThrow", dt)
             let next = this.nextVelocity(this.velocity)
             let prevLength = Points.length(this.velocity)