[Webkit-unassigned] [Bug 28815] New: Autoscrolling on mouse drag when WebView is clipped by superview

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=28815

           Summary: Autoscrolling on mouse drag when WebView is clipped by
                    superview
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Macintosh Intel
        OS/Version: Mac OS X 10.5
            Status: UNCONFIRMED
          Severity: Normal
          Priority: P2
         Component: New Bugs
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: opendarwin at lapcatsoftware.com


Overview:
If a WebView is partially clipped by its superview, even by 1 pixel, then a
strange mouse-dragging behavior can result: when you drag the mouse (for
example, to select some text), the WebView automatically scrolls downward
slowly. This does not occur if the WebView is not clipped by its superview.

Steps to Reproduce:
1. Unzip, open, build, and run the attached Sample Xcode project
WebViewAutoscroll
2. Enter http://webkit.org/ into both the left and right text fields to load
the page in both WebViews.
3. Click and drag the mouse to try to select some text in the first line of the
first paragraph, "WebKit is an open..."

Actual Results:
The WebView slowly autoscrolls downward.

Expected Results:
The WebView doesn't autoscroll.

Build Date & Platform:
git commit de240fc8d016a25d9f4b05f65195414375159b3c, corresponding to svn
r47855

Additional Builds and Platforms:
Also occurs with stock WebKit in Mac OS X 10.5.8 Build 9L30

Additional Information:
I've attached a sample Xcode project WebViewAutoscroll that demonstrates the
bug. The only difference between the two WebViews is that the y-origin of the
WebView on the left is set 1 pixel higher than the y-origin of the WebView on
the right, so that the WebView on the left is clipped by its superview. When
you build the project, you can see the CompileXIB warning "This view is clipped
by its superview." The autoscrolling bug occurs with the left WebView but not
with the right WebView.

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