- From: Robert O'Callahan <robert@ocallahan.org>
- Date: Tue, 13 Jan 2015 18:38:03 +1300
- To: Simon Fraser <smfr@me.com>
- Cc: "public-fx@w3.org" <public-fx@w3.org>
- Message-ID: <CAOp6jLYxUovD2R4PQJ_cOEoLEmnPfuu+w0fxq2d1_J=_7dvVPg@mail.gmail.com>
On Tue, Jan 13, 2015 at 5:21 PM, Simon Fraser <smfr@me.com> wrote: > On Jan 7, 2015, at 6:12 PM, Robert O'Callahan <robert@ocallahan.org> > wrote: > > > Testcase: > > <!DOCTYPE HTML> > > <body style="height:3000px"> > > <div style="overflow:hidden; width:300px; height:100px;"> > > <div style="filter:blur(10px); -webkit-filter:blur(10px);"> > > <div style="margin:30px; width:200px; height:200px; > background:blue;"></div> > > <div style="position:fixed; left:100px; top:50px; width:200px; > height:200px; background:yellow;"></div> > > Making the fixed-pos DIV "position:absolute" shows basically the same > problem. > > > > Currently Gecko and Blink both clip the yellow div to the > overflow:hidden element. Technically, per spec, they should not, since an > overflow:hidden element should only clip descendants for which it is a > containing block ancestor, which it is not in this case. > > > > However, if we were to try to follow the spec and not clip the yellow > div, it's totally unclear what should actually be rendered in this case: > > a) It seems pretty clear that the blur of the blue div should be clipped. > > b) It seems pretty clear that the blur of the yellow div should not be > clipped. > > c) But there are pixels in the blurred image that would receive > contributions from both the blue and yellow divs. > > > > A similar issue would arise if we used a filter that draws black in the > border-box of the filtered element. Which area, if any, outside the > overflow:hidden element would be drawn black? > > > > I see two plausible options: > > 1) Specify that 'filter' is a containing block for all positioned > descendants (like 'transform' already is). > > 2) Specify that 'filter' only filters descendants that have the filtered > element as a containing block ancestor. > > I prefer #1. Anyone got any better suggestions? > > > > This issue does not arise for 'opacity' or any other effect where > rendering is inherently restricted to the clipped bounds of the effect's > descendants. > > But Firefox and WebKit do clip the blue and yellow boxes if you replace > the filter with opacity. Chrome does not. > I considered that a Gecko bug, and fixed it yesterday :-). Though, to be honest, there's still a bug where if the overflow:hidden element is actually scrollable, we will still clip in some situations, when off-main-thread scrolling gets involved :-(. I could revert the fix if there's a consensus against it. Rob -- oIo otoeololo oyooouo otohoaoto oaonoyooonoeo owohooo oioso oaonogoroyo owoiotoho oao oboroootohoeoro oooro osoiosotoeoro owoiololo oboeo osouobojoeocoto otooo ojouodogomoeonoto.o oAogoaoiono,o oaonoyooonoeo owohooo osoaoyoso otooo oao oboroootohoeoro oooro osoiosotoeoro,o o‘oRoaocoao,o’o oioso oaonosowoeoroaoboloeo otooo otohoeo ocooouoroto.o oAonodo oaonoyooonoeo owohooo osoaoyoso,o o‘oYooouo ofooooolo!o’o owoiololo oboeo oiono odoaonogoeoro ooofo otohoeo ofoioroeo ooofo ohoeololo.
Received on Tuesday, 13 January 2015 05:38:36 UTC