[Webkit-unassigned] [Bug 34913] New: Unpainted white area appears at the edge of the page when body has bg color

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=34913

           Summary: Unpainted white area appears at the edge of the page
                    when body has bg color
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: PC
        OS/Version: All
            Status: UNCONFIRMED
          Severity: Normal
          Priority: P2
         Component: WebCore Misc.
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: kinuko at chromium.org


Created an attachment (id=48677)
 --> (https://bugs.webkit.org/attachment.cgi?id=48677)
Test case

The attached test page sometime shows unpainted white border areas at the left,
bottom and right edge of the page on my latest WebKit build and Nightly build
on Mac.
In most cases it renders ok, but if you intentionally move the mouse on the
browser while loading the page (thus forcing a repaint for hitTest during the
load) it often leaves the edges unpainted.

My understanding in repainting flow is limited, but to me it appears like a 
timing issue.  And also it's because our user-agent CSS (html.css) defines the
body has 8px 
margin by default, makes the area unpainted in some cases.

What I've observed is:
1. when a page is being loaded, WebKit first invalidates whole page area
several times (e.g. when stylesheet is loaded and etc) and then invalidates
smaller rects for DOM nodes when they are laid out.
2. RenderView asks WebKit to paint the invalidated rects, and WebKit first
tries to paint the root box area (i.e. #document node) with document->body()'s
background color.  This usually works well, but if the body hasn't been loaded
yet at this time WebKit doesn't do actual painting.
3. RenderView clears the invalidated rects after asking WebKit to paint whether
WebKit fill the whole page area or not.  Later WebKit generates another set of
invalidates for body and other nodes when they're being laid out, but the body
has 8px margin and WebKit doesn't paint the area.

Original issue is reported at: http://crbug.com/29880

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