Bug 39380 – Slow vertical scrolling when text is selected in nested divs

• Component: Layout and Rendering
• Status: RESOLVED DUPLICATE

[Nate Whetsell]

Created attachment 56520 [details]
100 div pairs in a div floated left

On OS X 10.6, selecting all the text in a webpage consisting of several (100 in the attached test documents) of these:

<div>
  <div class="float-left">
      [some text]
  </div>
</div>

produces sluggish vertical scrolling. (The "float-left" class is used to define a style for floating a div left: div.float-left{float:left;}).

If these snippets are enclosed in a div that is itself floated left (or right), both upward and downward scrolling are sluggish. If the snippets are enclosed in a div without a float style (or no div at all), only upward scrolling is sluggish. If no text is selected, scrolling is fast and smooth.

The sluggishness only occurs when text is inside a pair of divs; removing the outer div results in fast scrolling. Also, the inner div must be the one that's floated. If the outer div is floated, vertical scrolling while text is selected is fast.

Sluggish scrolling also occurs in Google Chrome. Firefox scrolls smoothly.

[Nate Whetsell]

Created attachment 56521 [details]
100 divs in a plain div (not floated)

[Alexey Proskuryakov]

Still happens with nightly r89812. Busy in RenderBlock::selectionGaps().

[Nate Whetsell]

This was fixed in <http://trac.webkit.org/r132545>.

*** This bug has been marked as a duplicate of bug 100413 ***