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

Milian Wolff milian.wolff at kdab.com
Thu Mar 29 06:23:37 PDT 2012

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 


[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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