- From: Rik Cabanier <cabanier@gmail.com>
- Date: Wed, 7 Aug 2013 20:10:46 -0700
- To: David Dailey <ddailey@zoominternet.net>
- Cc: Dirk Schulze <dschulze@adobe.com>, www-svg <www-svg@w3.org>, public-fx@w3.org
- Message-ID: <CAGN7qDBCB4qD+o_bJYpRUbCO9j2S+R8myuv_oLfad8WOZh78mQ@mail.gmail.com>
Hi David, the clipping paths in your example are all 'simple'. A complex clip contains more than 1 path. I see that there's a clip with a clip which does not make it complex. Rik On Wed, Aug 7, 2013 at 3:34 PM, David Dailey <ddailey@zoominternet.net>wrote: > I’m not sure if it is relevant or not, but the notion of intersecting > clipPaths is explored a bit in this example from about eight years ago. > IE/ASV could do it “properly” (as per this author’s common sense) at the > time. After a year or two Opera did it properly. A year or two ago Chrome > finally figured out how to handle the application of one clipPath to > another, though Safari doesn’t handle the JavaScript to SMIL business quite > right yet, although it and IE9 do manage the clipping okay. Firefox doesn’t > render anything of the example at right. **** > > ** ** > > http://srufaculty.sru.edu/david.dailey/svg/newstuff/clipPath4.svg**** > > ** ** > > cheers**** > > David**** > > ** ** > > *From:* Rik Cabanier [mailto:cabanier@gmail.com] > *Sent:* Wednesday, August 07, 2013 12:59 PM > *To:* Dirk Schulze > *Cc:* www-svg; public-fx@w3.org > *Subject:* Re: [css compositing] clipping and isolation**** > > ** ** > > ** ** > > On Wed, Aug 7, 2013 at 5:31 AM, Dirk Schulze <dschulze@adobe.com> wrote:** > ** > > Hi,**** > > > On Aug 7, 2013, at 11:05 AM, Rik Cabanier <cabanier@gmail.com> wrote: > > > The blending specification currently calls out that clipping should > introduce isolation [1]. > > So if you have content as follows: > > <circle id="a"/> > > <g clip-path="..."> > > <circle id="b" style="mix-blend-mode:difference"/> > > </g> > > circle 'b' won't blend with circle 'a'.**** > > I think we can not isolate this discussion just on SVG (pun). I cc'ed fxtf > mailing list, since it is a problem that hopefully should be fixed for CSS > clip-path in general and not just on SVG.**** > > > > > > I added this because we were worried that graphics libraries wouldn't > not be able to support this. > > Now that we started implementing the feature, it turns out that this > limitation is not needed when the browser uses the clipping capabilities of > the underlying graphics library. > > > > For 'simple' clips (that are the vast majority), all browsers use the > clipping code. > > However, for more complex clips, certain browsers turn the clip into a > mask and this will execute a different code path that does isolate. > > > > There are three options (from my least to most desired): > > 1. keep behavior as specified in the spec. > > 2. specify that complex clips cause isolation but not simple clips. > > 3. specify that clipping never isolates. Browsers will need to find a > way (ie planarization/path collapsing) to keep using the clipping code path. > >**** > > As you note, it always just has been a problem of complex clip-path > operations. A simple example is when you combine two paths with different > clip rules (winding rules). Many browsers traditionally did not use > clipping for these cases but masking operations. Masking operation usually > cause isolation. In our tests we figured out that this is not always the > case or not the case anymore: > > * Safari (one port of WebKit) does use masking, but did not have isolation > behavior. > * Blink uses a path planarizer in Skia to flatten the path and uses the > real clipping operation with this planarized path (in nearly all cases). > > On the other side: > * Firefox uses clipping for simple clip-path operations and isolated > masking on complex clipping. > * Same for all other WebKit ports than Safari. > > We could just test WebKit/Blink/Gecko based implementations where we had > the access to the source code. The isolated behavior can not be experienced > with simple source-over compositing as implemented today. So we could not > test if IE can implement clip-path in an not-isolating way. > > As a note, implementations that use masking for simulating clipping might > not follow the spec that requires aliased clipping anyway. Masking is > usually done drawing the mask onto an intermediate image buffer with AA. > > Solutions for implementations could be to look at path planarization (as > Blink does). There are some open source projects that try to do path > planarization. Some are quite good some at least not bad. I was told that > the Skia code is quite generic. So UAs with different graphic libraries can > look into splitting Skia for their own needs.**** > > ** ** > > Yes, it would be great to know if closed-source implementations can > implement this, or are willing to use a planarization library.**** > > As you note, this will also improve the quality and speed of complex clips. > **** > > **** > > > Clipping creates a stacking context (important for HTML). However, the > implementation is not different from the implementation in SVG. That is why > it makes sense to look at the feature itself and don't split the discussion > into HTML and SVG.**** > > ** ** > > If it creates a stacking context, a clip in HTML should causes isolation > according to the compositing spec. [1]**** > > 2D transforms had the same issue and people insisted that we force them > into isolation.**** > > ** ** > > Maybe we can keep the current defintion and fix this in the next revision > of the spec where we introduce non-isolated groups.**** > > ** ** > > **** > > > I should say that I am in favor for not-isolated behavior on clipping, but > it needs some work in implementations that do masking to simulate complex > clipping. > > Greetings, > Dirk**** > > **** > > 1: http://www.w3.org/TR/compositing-1/#csscompositingrules_CSS **** > > ** ** >
Received on Thursday, 8 August 2013 03:11:14 UTC