Updates

heap.js

@@ -105,6 +105,7 @@ var LINE_COLOR  = BLUE;
 var TEXT_COLOR  = DARKGREY;
 var ALGO_SPEED  = 1;
 var ALGO_STATUS = 'stopped';
+var USER_PAUSED = false; 
 
 // these will change dependent on the above params
 var BOX_DIM     = DEF_BOX_DIM;
@@ -119,6 +120,16 @@ var PAUSE_CONTROLLER;
 var SWAPS    = [];
 var SWAP_IDX = 0;
 
+function handleVisibilityChange() {
+    if (document.hidden && ALGO_STATUS === "running") {
+        ALGO_STATUS = "paused";
+    }
+    if (!document.hidden && ALGO_STATUS === "paused" && !USER_PAUSED) {
+        ALGO_STATUS = "running";
+    }
+}
+document.addEventListener("visibilitychange", handleVisibilityChange);
+
 
 function createNode( x, y, z, i, format ) {
 
@@ -775,14 +786,17 @@ function runFunc( pcFunc, userFunc, button  ) {
             button.name('pause');
             button.updateDisplay();
             pcFunc();
+            USER_PAUSED = false;
         }else if (ALGO_STATUS === "running") {
             ALGO_STATUS = "paused";
             button.name('resume');
             button.updateDisplay();
+            USER_PAUSED = true;
         }else if (ALGO_STATUS === "paused") {
             ALGO_STATUS = "running";
             button.name('pause');
             button.updateDisplay();
+            USER_PAUSED = false;
         }
     } else {
         userFunc();