UX: fix jerky UI when creating new posts

- do not scroll screen if post is already on screen
- do not hide/show suggested topics each time you post
- be less aggressive about setting scrollTop in LockOn

vendor/assets/javascripts/lock-on.js

@@ -1,3 +1,21 @@
+// Dear traveller, you are entering a zone where we are at war with the browser
+// the browser is insisting on positioning scrollTop per the location it was in
+// the past, we are insisting on it being where we want it to be
+// The hack is just to keep trying over and over to positiong the scrollbar (up to 1 minute)
+//
+// The root cause is that a "refresh" on a topic page will almost never be at the
+// same position it was in the past, the URL points to the post at the top of the
+// page, so a refresh will try to bring that post into view causing drift
+//
+// Additionally if you loaded multiple batches of posts, on refresh they will not
+// be loaded.
+//
+// This hack leads to a slight jerky experience, however other workarounds are more
+// complex, the 2 options we have are
+//
+// 1. onbeforeunload ensure we are scrolled to the right spot
+// 2. give up on the scrollbar and implement it ourselves (something that will happen)
+
 (function (exports) {
 
   var scrollEvents = "scroll.lock-on touchmove.lock-on mousedown.lock-on wheel.lock-on DOMMouseScroll.lock-on mousewheel.lock-on keyup.lock-on";
@@ -19,11 +37,15 @@
   LockOn.prototype.lock = function() {
     var self = this,
         previousTop = this.elementTop(),
-        startedAt = new Date().getTime()
+        startedAt = new Date().getTime(),
         i = 0;
 
     $(window).scrollTop(previousTop);
 
+    var within = function(threshold,x,y) {
+      return Math.abs(x-y) < threshold;
+    };
+
     var interval = setInterval(function() {
       i = i + 1;
 
@@ -31,20 +53,24 @@
           scrollTop = $(window).scrollTop();
 
       if (typeof(top) === "undefined") {
-        $('body,html').off(scrollEvents)
+        $('body,html').off(scrollEvents);
         clearInterval(interval);
         return;
       }
 
-      if ((top !== previousTop) || (scrollTop !== top)) {
+      if (!within(4, top, previousTop) || !within(4, scrollTop, top)) {
         $(window).scrollTop(top);
+        // animating = true;
+        // $('html,body').animate({scrollTop: parseInt(top,10)+'px'}, 200, 'swing', function(){
+        //   animating = false;
+        // });
         previousTop = top;
       }
 
-      // We commit suicide after 1s just to clean up
+      // We commit suicide after 3s just to clean up
       var nowTime = new Date().getTime();
       if (nowTime - startedAt > 1000) {
-        $('body,html').off(scrollEvents)
+        $('body,html').off(scrollEvents);
         clearInterval(interval);
       }
 
@@ -55,7 +81,7 @@
         $('body,html').off(scrollEvents);
         clearInterval(interval);
       }
-    })
+    });
 
   };