I am guessing this is because either or both of visible rect and clip rect now takes into account of filter expansion?

Also if you resize window enough to have vertical scrollbar, you can see the compositted div move when you scroll.


On the other hand, even without the the blur filter, I can still see difference in rendering on the column of stars on the right. So maybe we have more than one problem here.

Talked w/ ajuma@, turns out there are three things at play here:
1. There was a visible rect bug that is fixed later, that explains the bouncing around when scrolling.

2. On compositor thread, image-mask is applied after blur filter (with expanded rect), while on main thread (and other browsers) image-mask is applied before blur filter.

3. The difference in the last row of stars is because of how we scale while raster. It is visible when we turn off both image-mask and filter, and the picture is a 2 by 2 image, scaled to fill the diff, and that looks different.