Re: Utility of background-composite and background-blend-mode?

On Thu, Mar 14, 2013 at 10:21 AM, L. David Baron <dbaron@dbaron.org> wrote:

> On Thursday 2013-03-14 09:55 -0700, Rik Cabanier wrote:
> > On Thu, Mar 14, 2013 at 9:19 AM, L. David Baron <dbaron@dbaron.org>
> wrote:
> >
> > > On Thursday 2013-03-14 05:44 -0700, Dirk Schulze wrote:
> > > > No, not WebKit's rules. And I do not think that we want to specify
> > > > buffering. A behavior in situations like scrolling for blending
> > > > should be specified and browser need to follow. I see that this
> > > > can be challenging but would be most desireabale. After all,
> > > > scrolling should not affect the browser experience of the user on
> > > > the visual side - especially for blending.
> > >
> > > As I said in http://dbaron.org/log/20130306-compositing-blending , I
> > > think there's a lot less to specify and a lot less to drive towards
> > > interoperability if compositing and blending operations are limited
> > > to things that create stacking contexts.  This limitation would be
> > > present if background-blend-mode and background-composite are
> > > dropped, which I think should be done.
> >
> >
> > David,
> > the exact same issue will happen if blending applies to elements (in
> which
> > case stacking contexts are created).
> > For instance, an element with blending that is a child of an element that
> > uses fixed positioning will render differently today in FF and WK.
> >
> > Dropping background-blend-mode will not solve this problem.
>
> Dropping background-blend-mode simplifies it a lot, because you only
> have to consider elements that form stacking contexts when
> addressing it.


Maybe I'm not seeing the problem that makes background-blend-mode harder.
What would be the difference between:

<div style="position: fixed">

<img src="ducky.png" style="mix-blend-mode: multiply">

and

<div style="position:
fixed;backgound:url('ducky.png');background-blend-mode:multiply">

Both will render differently because 'position:fixed' creates an offscreen
buffer in WK but not in FF