[Webkit-unassigned] [Bug 55416] New: Viewport no longer allows an auto value for "user-scalable", we lost the "default" keyword.

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=55416

           Summary: Viewport no longer allows an auto value for
                    "user-scalable", we lost the "default" keyword.
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: PC
        OS/Version: Mac OS X 10.5
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebCore Misc.
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: joepeck at webkit.org
                CC: ddkilzer at webkit.org, koivisto at iki.fi,
                    kenneth at webkit.org


With the ViewportArguments change in r67376 the "default" keyword which explicitly
meant "auto" was lost. More noticeable is that the "user-scalable" argument lost
the concept of auto altogether and now is only true or false (was float, now bool):
http://trac.webkit.org/changeset/67376

This is problematic if the browser wants to set a default user-scalable value. It always
sees the Viewport coming from WebCore as an explicit true or false, never a "undefined
value, use default or auto". Also previously, the "default" keyword provided users
with the option of changing the viewport from something they set explicitly, to fallback
to the browser default. That is no longer possible.

I don't think this concept is mentioned in the "css-viewport" spec, but this is a
regression from former behavior and functionality:
http://people.opera.com/rune/TR/css-viewport/

The "auto/default" value is a browser level concept, so it doesn't look like there
is an obvious solution in ViewportArguments. This is problematic since
ViewportArguments::computeViewportAttributes does nice validation/processing
of user-scalable (automatically equating max/min/initial scale). An ideal solution
would not require duplicating that validation.

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