Created attachment 47733 [details] Test page using elementFromPoint Setting overflow:hidden on <td> elements inside a large table increases the amount of time needed to hit test points within the table. This is just a special case of https://bugs.webkit.org/show_bug.cgi?id=33520 - setting overflow:hidden gives each <td> its own RenderLayer, so hit testing within the element causes a lot of very slow coordinate maps. The other issue is that currently when hit testing inside a table we iterate through every child cell instead of taking advantage of rows to restrict the search. This shows up as a 30-50ms delay on an internal app with a large table embedded at a moderate depth inside the DOM (roughly 10 RenderLayers from the document root).
overflow:hidden causes each TD to get its own layer. The patch in https://bugs.webkit.org/show_bug.cgi?id=33520 speeds hit testing up
Pah, bugzilla was a bit overeager. What I meant was: overflow:hidden causes each TD to get its own RenderLayer. The patch in https://bugs.webkit.org/show_bug.cgi?id=33520 speeds this test up by about 33%.