310087 - Be smarter about handling of newlines in pre and pre-wrap content

Status: RESOLVED FIXED

(Core :: Layout: Block and Inline, defect, P2)

Description

[Boris Zbarsky [:bzbarsky]]

See bug 240933 comment 9 and bug 240933 comment 10.  The following are the
issues I see:

1)  I'm not sure we set break types on lines appropriately based on \n in
preformatted content.  At least part of the problem is that changing the
white-space handling just does a reflow and I believe break types survive across
reflows, right?  If so, we'd need to deal with that.  In any case, we return
this stuff correctly from nsTextFrame::Reflow, so at least some of this already
works.  If we had this, working we could use it to optimize dirtying of lines
when content is changed while editing.  

2)  The check for BRFrame in nsBlockFrame::AddFrames should actually check
whether the prevsibling would cause a break-after, not check for a BRFrame.

3)  It looks like we already call SetLineEndsInBR from nsTextFrame::Reflow, so
that should be ok (though perhaps we should rename this or clarify how it
interacts with the break-after stuff, or something?)

Comment 1

[Boris Zbarsky [:bzbarsky]]

I can write some testcases if we need to test things, btw.

Comment 2

[Robert O'Callahan (:roc) (email my personal email if necessary)]

We could easily make changes to 'white-space' cause a reframe.

Comment 3

[Boris Zbarsky [:bzbarsky]]

Does the reframe clear out info on lines somehow, then?  If the info is not
stored between reflows, there's nothing to worry about, it seems...

Comment 4

[Robert O'Callahan (:roc) (email my personal email if necessary)]

What information are you talking about, exactly?

On line boxes, SetLineBreakBefore/After is only about clearance, so not relevant
here. SetLineWrapped gets recomputed every time we reflow the line.

Comment 5

[Boris Zbarsky [:bzbarsky]]

Ah.  I didn't realize the line break thing was just for clearance.  I really
wish we had more docs in nsLineBox.h.... ;)

I guess the only relevant part then is the LineEndsInBR() thing, and that's
recomputed each time we reflow the line too.

Comment 6

[Boris Zbarsky [:bzbarsky]]

Attachment: Testcase with -moz-pre-wrap

Comment 7

[Boris Zbarsky [:bzbarsky]]

Attachment: Testcase with <br>

The <br> testcase is actually slower.  This has been happy ever since bug 229052 added that SetLineEndsInBR() call to nsTextFrame::Reflow.

So only item 2 is left, really.  Should be easy to fix.

Comment 8

[Boris Zbarsky [:bzbarsky]]

Attachment: Like so

Comment 9

[Boris Zbarsky [:bzbarsky]]

Fixed on trunk.