(Sorry for the delayed reply. I was out for a long weekend.) On Thu, Mar 14, 2013 at 1:42 PM, Simon Fraser <smfr@me.com> wrote: > On Mar 14, 2013, at 11:21 AM, Rik Cabanier <cabanier@gmail.com> wrote: > > > On Thu, Mar 14, 2013 at 11:04 AM, Simon Fraser <smfr@me.com> wrote: > > From the spec: > > Each background image will blend with the element's background and the > background images at a lower z-index > > > So, it will blend between elements. > > > Wait, so it will blend with only the background images of other elements, > not their foreground? > The background images is drawn as specified by the CSS painting order [1] 7.2.1.2 states when background images are drawn. As David stated in his blog post [2], 'grouping' is not specified in this spec. For the current behavior of simple source-over compositing, there is no need to specify this since that alpha compositing is associative [3]. Blending unfortunately is not so it needs this. Because of this, you never know if a stacking context creates an offscreen bitmap so it that context contains a blended element, that element's appearance is undefined. What we need to do, is come up with a set of conditions that should create offscreen bitmaps and then enforce them if absence of an offscreen bitmap would create a visual difference. 1: http://www.w3.org/TR/CSS21/zindex.html 2: http://dbaron.org/log/20130306-compositing-blending 3: http://en.wikipedia.org/wiki/Alpha_compositing
Received on Monday, 18 March 2013 03:25:46 UTC