Bug 383524

Comment 1 Tim Buschtoens 2012-07-10 11:30:38 EDT

Fixed with commit 7eb91b26e0247a3fd42bb037cb9adac3e143cc37.

Supported are heights between the default height and the height of the grid. Other heights may behave strange or produce render glitches.

A word on performance:

I did not get any noticale perfromance decline in a grid/tree/table without custom item heights now compared to before the implementation of this feature. 

Generally speaking, chrome is super fast, IE9 is not quite as good but still nice, and a current firefox is bearable when no add-ons are installed. On my default firefox with firebug and some other stuff installed its almost as slow as in IE8. 

A grid with many custom heights may be somewhat slower especially in firefox. However, this seems to be due to the additional layouting work for the rows, not because of the (now more complex) calculation of the topitem/index. I adjusted the scrollbars auto scrollevent-merge feature, so that it does not immediately kick in on firefox. In IE7 it will kick in right after the first rendering.

While there is some room for improvement when calculationg topitem/topindex, measurements in IE9 show that it only needs about 1/4 of the time required for dom-rendering, not counting the actual graphical rendering. The firebug performance measurements tool did not produce any really useful results, but it did seem that most of the time is also spent on rendering, not calculating the item. And i'm not sure we can improve the actual rendering much more.

So unless we get complaints, i would not try to tweak performance anymore.