Firefox sacrifices beauty in order to end browser freeze
Wed 10 Feb 2016
A new post at mozilla.org announces that Firefox 46 will finally cure the browser freeze syndrome known as ‘jank’ – the moment where scrolling becomes impossible because of a backlog of instructions – but that this improvement will cause some undesirable user experiences as well.
‘Of course, nothing is free, and APZ comes at a cost. APZ does eliminate jank, but in some cases it does so by checkerboarding instead. Checkerboarding is what you get when you scroll faster than the browser can paint the page. When this happens, the content at your new scroll position hasn’t been painted yet, and so we just show a flat background color. (The term checkerboarding comes from the original iPhone implementation, which would show a checkerboard pattern.) Once the painting catches up, the content fills in.’
‘Checkerboarding’ refers to the grid pattern which was seen in analogous scrolling circumstances in the earliest versions of the iPhone. In the field of graphics, the checkerboard is intended to represent transparency, or absence of pixel content.
The Mozilla post says that it was decided to trade jank freezes for what may prove to be a perplexing scrolling experience (particularly in complex pages or pages which employ lazy loading or scroll-driven effects, such as graphs which animate when they come into view) in order to avoid hangs, which are frequently mistaken for freeze loops. In such circumstances it is not always clear to the user whether a freeze has become critical, and frustrated attempts to clear the hang are likely to aggravate it.