[webkit-dev] Unit Test for Page Breaks / absolute coordinates in PrintContext::pageNumberForElement

[Milian Wolff]

On Thursday 29 March 2012 13:06:12 David Hyatt wrote:
> Do you have a bug for this work? I'm not really sure what you're trying to
> accomplish… avoiding page breaks in a table row does not seem correct to
> me.

See https://bugs.webkit.org/show_bug.cgi?id=82617

The reason is that without this patch / work, page breaks sometimes occur in 
the middle of table rows, resulting in unreadable text garbage. If you doubt 
it, I can change the example in the bug above a bit to visualize this.

Bye

> On Mar 29, 2012, at 8:23 AM, Milian Wolff wrote:
> > Hey there,
> > 
> > I'm trying to write a unit test for my layouting patch, that prevents page
> > breaks in table rows. So far, I've extended the layoutTestController with
> > a
> > pageBreaksInElementById function, similar to pageNumberForElementById.
> > 
> > The logic behind the implementation is basically an extended copy of
> > PrintContext::pageNumberForElement, see e.g. [1].
> > 
> > Now in my unit test, I call this function for every table row and "ensure"
> > that the return value is always 0, i.e. no page break. Turns out, that
> > this
> > does not work as expected: My table layouting code [2] takes the offset of
> > the surrounding table into account, and the visual result looks OK. The
> > unit test code ([1]) though apparently assumes absolute coordinates,
> > which (I think?!) box->pixelSnappedOffsetLeft() is *not*. What could be
> > used instead? Also, doesn't this also mean that the logic of
> > PrintContext::pageNumberForElement is flawed for nested elements that are
> > offsetted?
> > 
> > Note btw. that the box does not have any layout state when called from
> > PrintContext::pageBreaksInElement, as such I cannot simply add a call to
> > RenderBlock::offsetFromLogicalTopOfFirstPage().
> > 
> > Thanks
> > 
> > [1]: http://paste.kde.org/448514/
> > [2]: http://paste.kde.org/448520/
-- 
Milian Wolff | milian.wolff at kdab.com | Software Engineer
KDAB (Deutschland) GmbH&Co KG, a KDAB Group company
Tel. Germany +49-30-521325470, Sweden (HQ) +46-563-540090
KDAB - Qt Experts - Platform-independent software solutions
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