From 1385d19f64ec03f9e08d4621e609cd6dbfa72ac9 Mon Sep 17 00:00:00 2001
From: Julian Lam <julian@nodebb.org>
Date: Wed, 30 Mar 2016 18:10:03 -0400
Subject: [PATCH] Further tweaks to viewport shuffling and dynamic image
 loading

@BenLubar
---
 public/less/global.less          |   2 +-
 public/src/client/topic/posts.js | 119 ++++++++++++++++---------------
 public/src/modules/navigator.js  |  18 +++--
 3 files changed, 73 insertions(+), 66 deletions(-)

diff --git a/public/less/global.less b/public/less/global.less
index d9f16c74e8..d606b8221c 100644
--- a/public/less/global.less
+++ b/public/less/global.less
@@ -14,7 +14,7 @@
 
 	&[data-state="unloaded"], &[data-state="loading"] {
 		display: inherit;
-		height: 1rem;
+		height: 0;
 		opacity: 0;
 	}
 
diff --git a/public/src/client/topic/posts.js b/public/src/client/topic/posts.js
index 5823d81b65..2cbe2a0d2a 100644
--- a/public/src/client/topic/posts.js
+++ b/public/src/client/topic/posts.js
@@ -10,7 +10,9 @@ define('forum/topic/posts', [
 	'components'
 ], function(pagination, infinitescroll, postTools, navigator, components) {
 
-	var Posts = {};
+	var Posts = {
+		_imageLoaderTimeout: undefined
+	};
 
 	Posts.onNewPost = function(data) {
 		if (!data || !data.posts || !data.posts.length) {
@@ -240,70 +242,74 @@ define('forum/topic/posts', [
 		images.each(function() {
 			$(this).attr('data-src', $(this).attr('src'));
 			$(this).attr('data-state', 'unloaded');
-			$(this).attr('src', 'data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7');
+			$(this).attr('src', 'about:blank');
 		});
-
-		$(window).scrollTop(scrollTop + $(document).height() - height);
 	};
 
 	Posts.loadImages = function(threshold) {
-		/*
-			If threshold is defined, images loaded above this threshold will modify
-			the user's scroll position so they are not scrolled away from content
-			they were reading. Images loaded below this threshold will push down content.
+		if (Posts._imageLoaderTimeout) {
+			clearTimeout(Posts._imageLoaderTimeout);
+		}
 
-			If no threshold is defined, loaded images will push down content, as per
-			default
-		*/
+		Posts._imageLoaderTimeout = setTimeout(function() {
+			/*
+				If threshold is defined, images loaded above this threshold will modify
+				the user's scroll position so they are not scrolled away from content
+				they were reading. Images loaded below this threshold will push down content.
 
-		var images = components.get('post/content').find('img[data-state="unloaded"]'),
-			visible = images.filter(function() {
-				return utils.isElementInViewport(this);
-			}),
-			scrollTop = $(window).scrollTop(),
-			adjusting = false,
-			adjustQueue = [],
-			adjustPosition = function() {
-				adjusting = true;
-				oldHeight = document.body.clientHeight;
+				If no threshold is defined, loaded images will push down content, as per
+				default
+			*/
 
-				// Display the image
-				$(this).attr('data-state', 'loaded');
-				newHeight = document.body.clientHeight;
+			var images = components.get('post/content').find('img[data-state="unloaded"]'),
+				visible = images.filter(function() {
+					return utils.isElementInViewport(this);
+				}),
+				scrollTop = $(window).scrollTop(),
+				adjusting = false,
+				adjustQueue = [],
+				adjustPosition = function() {
+					adjusting = true;
+					oldHeight = document.body.clientHeight;
 
-				var imageRect = this.getBoundingClientRect();
-				if (imageRect.top < threshold) {
-					scrollTop = scrollTop + (newHeight - oldHeight);
-					$(window).scrollTop(scrollTop);
-				}
-
-				if (adjustQueue.length) {
-					adjustQueue.pop()();
-				} else {
-					adjusting = false;
-				}
-			},
-			oldHeight, newHeight;
-
-		// For each image, reset the source and adjust scrollTop when loaded
-		visible.attr('data-state', 'loading');
-		visible.each(function(index, image) {
-			image = $(image);
-
-			image.on('load', function() {
-				if (!adjusting) {
-					adjustPosition.call(this);
-				} else {
-					adjustQueue.push(adjustPosition.bind(this));
+					// Display the image
+					$(this).attr('data-state', 'loaded');
+					newHeight = document.body.clientHeight;
+
+					var imageRect = this.getBoundingClientRect();
+					if (imageRect.top < threshold) {
+						scrollTop = scrollTop + (newHeight - oldHeight);
+						$(window).scrollTop(scrollTop);
+					}
+
+					if (adjustQueue.length) {
+						adjustQueue.pop()();
+					} else {
+						adjusting = false;
+					}
+				},
+				oldHeight, newHeight;
+
+			// For each image, reset the source and adjust scrollTop when loaded
+			visible.attr('data-state', 'loading');
+			visible.each(function(index, image) {
+				image = $(image);
+
+				image.on('load', function() {
+					if (!adjusting) {
+						adjustPosition.call(this);
+					} else {
+						adjustQueue.push(adjustPosition.bind(this));
+					}
+				});
+
+				image.attr('src', image.attr('data-src'));
+				if (image.parent().attr('href')) {
+					image.parent().attr('href', image.attr('data-src'));
 				}
+				image.removeAttr('data-src');
 			});
-
-			image.attr('src', image.attr('data-src'));
-			if (image.parent().attr('href')) {
-				image.parent().attr('href', image.attr('data-src'));
-			}
-			image.removeAttr('data-src');
-		});
+		}, 250);
 	};
 
 	Posts.wrapImagesInLinks = function(posts) {
@@ -318,13 +324,10 @@ define('forum/topic/posts', [
 	Posts.showBottomPostBar = function() {
 		var mainPost = components.get('post', 'index', 0);
 		var posts = $('[component="post"]');
-		var height = $(document).height();
 		if (!!mainPost.length && posts.length > 1 && $('.post-bar').length < 2) {
 			$('.post-bar').clone().appendTo(mainPost);
-			$(window).scrollTop($(window).scrollTop() + $(document).height() - height);
 		} else if (mainPost.length && posts.length < 2) {
 			mainPost.find('.post-bar').remove();
-			$(window).scrollTop($(window).scrollTop() - $(document).height() - height);
 		}
 	};
 
diff --git a/public/src/modules/navigator.js b/public/src/modules/navigator.js
index 6877abe8db..3d65f6b8a0 100644
--- a/public/src/modules/navigator.js
+++ b/public/src/modules/navigator.js
@@ -121,20 +121,24 @@ define('navigator', ['forum/pagination', 'components'], function(pagination, com
 			}
 		});
 
+		var atTop = scrollTop === 0 && parseInt(els.first().attr('data-index'), 10) === 0,
+			nearBottom = scrollTop + windowHeight > documentHeight - 100 && parseInt(els.last().attr('data-index'), 10) === count - 1;
 
-		// check if we are at the top
-		if (scrollTop === 0 && parseInt(els.first().attr('data-index'), 10) === 0) {
+		if (atTop) {
 			index = 1;
-		// check if we are near the bottom
-		} else if (scrollTop + windowHeight > documentHeight - 100 && parseInt(els.last().attr('data-index'), 10) === count - 1) {
+		} else if (nearBottom) {
 			index = count;
 		}
 
 		// If a threshold is undefined, try to determine one based on new index
 		if (threshold === undefined) {
-			var anchorEl = components.get('post/anchor', index - 1);
-			var anchorRect = anchorEl.get(0).getBoundingClientRect();
-			threshold = anchorRect.top;
+			if (atTop) {
+				threshold = 0;
+			} else {
+				var anchorEl = components.get('post/anchor', index - 1);
+				var anchorRect = anchorEl.get(0).getBoundingClientRect();
+				threshold = anchorRect.top;
+			}
 		}
 
 		if (typeof navigator.callback === 'function') {