From 8190cdc9fb6c929a92d8624099dd1cee3bed8770 Mon Sep 17 00:00:00 2001
From: Steve Howell <steve@zulip.com>
Date: Sun, 11 Aug 2013 15:34:05 -0400
Subject: [PATCH] Avoid redundant O(N) work in unfade_messages()..

The code in unfade_messages() is O(N) over the number of
messages, but a simple flag allows us to track the fact that
all messages are unfaded, so we can short circuit the O(N)
logic in many cases.

A typical scenario now would be that you start typing a
stream while the topic is still empty.  Modulo debouncing,
every keystroke now leads to a call to unfade_messages(),
but this change only does real work the first time.

(imported from commit da07cf408bbdbf5b381ff3ec33a5e05e34eef5b5)
---
 static/js/compose_fade.js | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/static/js/compose_fade.js b/static/js/compose_fade.js
index de2c27ee05..f0d39bb8a9 100644
--- a/static/js/compose_fade.js
+++ b/static/js/compose_fade.js
@@ -3,6 +3,7 @@ var compose_fade = (function () {
 var exports = {};
 
 var focused_recipient;
+var any_messages_faded = false;
 
 exports.set_focused_recipient = function (recipient) {
     focused_recipient = recipient;
@@ -13,8 +14,15 @@ exports.unfade_messages = function (clear_state) {
         return;
     }
 
+    if (!any_messages_faded) {
+        return;
+    }
+
     rows.get_table(current_msg_list.table_name).find(".recipient_row, .message_row")
                                                .removeClass("faded").addClass("unfaded");
+
+    any_messages_faded = false;
+
     if (clear_state === true) {
         focused_recipient = undefined;
     }
@@ -52,6 +60,7 @@ function _update_faded_messages() {
             if (!elt.hasClass("faded")) {
                 elt.removeClass("unfaded").addClass("faded");
             }
+            any_messages_faded = true;
         } else {
             if (!elt.hasClass("unfaded")) {
                 elt.removeClass("faded").addClass("unfaded");