[Webkit-unassigned] [Bug 38443] Flash video in iframe stays on top of everything (no matter what z-index)

Wed May 19 18:49:51 PDT 2010

https://bugs.webkit.org/show_bug.cgi?id=38443

--- Comment #9 from Jon Honeycutt <jhoneycutt at apple.com>  2010-05-19 18:49:51 PST ---
> Note that all browsers in all platforms we've tried--except for WebKit on Windows--seem to implement this differently.  We checked Firefox-Mac, Firefox-Windows, WebKit-Mac, IE-Win, and Opera-Mac.  (It doesn't help to sandbox the iframe, as this gives rise to a whole new set of issues, see e.g. https://bugs.webkit.org/show_bug.cgi?id=39219).

The behavior of browsers here is varied; Firefox-win 3.6 puts the div on top, but in my testing, Firefox-win 3.5 doesn't, IE8 doesn't, and Opera-win 10.53 doesn't, so I don't see that WebKit on Windows is an outlier. Which versions of IE and Firefox did you test?

> 
> My question is: what's so special about Flash objects (or any plugin for that matter) that makes them have layering priority over *all* other HTML elements?  Please correct if I'm mistaken, but it seems to me that such 'power' is unique to plugins; other HTML elements nicely obey z-indices.  We have only experienced this overlap issue with Flash videos.

On Windows, Flash can paint with or without its own window. If it uses a window for painting, this window is a child window of the WebView, so it will paint on top of all other content in the WebView. If it paints without using a window, it draws into a layer that WebKit can composite with the rest of the page.

This is controlled by the wmode attribute; see http://kb2.adobe.com/cps/155/tn_15523.html.

Firefox-win 3.6.3 does have some interesting behavior where they allow opaque content to appear to layer on top of a windowed plug-in, but this seems a little strange to me, and I'm not yet sure that we need to match that behavior.

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