I need a pretty picture to explain my problem:
http://people.mozilla.org/~prouget/scrollIssue.png
A typical mechanism in mobile web browsers is to hide the browser
toolbar as the user scrolls. A way to do it in HTML, with Gecko (I
believe this is how it works in Firefox OS), is to have a container
around the toolbar and the mozbrowser iframe (of the size of the
viewport), and set mozgrab to true to this container. Then on scroll,
the container scrolls first, and then the content.
A thing I would like to be able to do is to show the toolbar back at
anytime, without requiring the user to scroll.
Showing the toolbar by scrolling the chrome will move the content. We
want the content to stay in place. I tried to scroll the parent and
the child process in opposite directions. It works, but it's choppy
and not at all seamless. I use the DOM (scrollBy/scrollTop) on the
body and on the content, which implies a round trip between the main
process and the child process, when everything could just be done in
the main process (where the compositor lives).
Any idea how I could achieve this effect in a efficient way? I was
thinking about changing (and animating) the scroll position of the
content from the main process. Maybe finding a way to make
`scrollBy{behavior: 'smooth'}` for content and parent to be synced… I
don't know. Does that make sense? If so, how to build that? If not,
any alternative way to show this toolbar?
I'm not sure I'm clear. The picture above should help.
-- Paul
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