From ba01c66d6456aa2f4c08336d6e5062bef9e5f595 Mon Sep 17 00:00:00 2001
From: Simon Lydell <simon.lydell@gmail.com>
Date: Thu, 2 Jun 2016 17:15:39 +0200
Subject: [PATCH] Drastically speed up `find_from_top_of_viewport`

- Don't recurse into children of elements when looking for visible text
  nodes; we'll get to them anyway since we iterate over every element of
  the page.
- Don't bother checking text nodes that we already know are whitespace
  only.

Fixes #747.
---
 extension/lib/viewport.coffee | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/extension/lib/viewport.coffee b/extension/lib/viewport.coffee
index 5591141..dd315a0 100644
--- a/extension/lib/viewport.coffee
+++ b/extension/lib/viewport.coffee
@@ -98,15 +98,21 @@ getFirstNonWhitespace = (element) ->
   viewport = getWindowViewport(window)
   for node in element.childNodes then switch node.nodeType
     when 3 # TextNode.
-      firstVisibleOffset = getFirstVisibleOffset(node, viewport)
-      if firstVisibleOffset?
-        offset = node.data.slice(firstVisibleOffset).search(/\S/)
-        return [node, firstVisibleOffset + offset] if offset >= 0
+      continue unless /\S/.test(node.data)
+      offset = getFirstVisibleNonWhitespaceOffset(node, viewport)
+      return [node, offset] if offset >= 0
     when 1 # Element.
       result = getFirstNonWhitespace(node)
       return result if result
   return null
 
+getFirstVisibleNonWhitespaceOffset = (textNode, viewport) ->
+  firstVisibleOffset = getFirstVisibleOffset(textNode, viewport)
+  if firstVisibleOffset?
+    offset = textNode.data.slice(firstVisibleOffset).search(/\S/)
+    return firstVisibleOffset + offset if offset >= 0
+  return -1
+
 getFirstVisibleOffset = (textNode, viewport) ->
   {length} = textNode.data
   return null if length == 0
@@ -146,12 +152,15 @@ getFirstVisibleText = (window, viewport) ->
       return result if result
       continue
 
-    continue unless Array.some(element.childNodes, utils.isNonEmptyTextNode)
+    nonEmptyTextNodes =
+      Array.filter(element.childNodes, utils.isNonEmptyTextNode)
+    continue if nonEmptyTextNodes.length == 0
 
     continue if utils.checkElementOrAncestor(element, utils.isPositionFixed)
 
-    result = getFirstNonWhitespace(element)
-    return result if result
+    for textNode in nonEmptyTextNodes
+      offset = getFirstVisibleNonWhitespaceOffset(textNode, viewport)
+      return [textNode, offset] if offset >= 0
 
   return null
 
@@ -291,6 +300,7 @@ module.exports = {
   adjustRectToViewport
   getAllRangesInsideViewport
   getFirstNonWhitespace
+  getFirstVisibleNonWhitespaceOffset
   getFirstVisibleOffset
   getFirstVisibleRange
   getFirstVisibleText
-- 
2.39.3