839802 - Print selection doesn't honor percent heights (because it doesn't have anything to resolve them against)

Status: NEW

(Core :: Printing: Output, defect)

Description

[Julian Viereck]

This is a followup bug to do a "proper" fix for the problem reported in bug #830278.

A possible reason for the high memory usage is presented in bug #830278 comment #c13.

Comment 1

[Julian Viereck]

Attachment: Reduction - WIP

I talked to dholbert on IRC about this: http://irclog.gr/#show/irc.mozilla.org/developers/464458

He pointed out "we probably need to first figure out why print-selection isn't working _at all_ for PDF.js". 

Based on that I've started to create a simple reduction of the problem. The version attached here doesn't use the printCallback so far but is already causing an issue. The height of the printed divs are different depending on the "print-selection-only" mode enabled or disabled. Is this a bug or a feature?

Comment 2

[Julian Viereck]

Attachment: Demonstration of issue presented in "Reduction - WIP"

This output was generated by selecting the "Some text on the first page." string, print the document, select "Print Selection Only" and choose "PDF -> Save as PDF..." from the print dialog on OSX.

The border of the div takes up the entire page when printing without "Print Selection Only" enabled, but as shown here, if the option is turned on, the height is way less.

Comment 3

[Daniel Holbert [:dholbert]]

The behavior-difference there happens because in print-selection, we don't have a containing-block-height to resolve our "height: 100%" values against (because we're just printing to an as-tall-as-it-needs-to-be container)

So the "100%" ends up being treated as "auto" -- that's how percent-heights behave when they don't have anything to resolve against.

(If you replace those 100% values with "auto", you'll see what I mean, in a normal print job.)

Comment 4

[Daniel Holbert [:dholbert]]

(In reply to Julian Viereck from comment #1)
> He pointed out "we probably need to first figure out why print-selection
> isn't working _at all_ for PDF.js". 

FWIW, it might be worth dedicating a bug *just to this part* (whether that's this bug, re-purposed to be about rendering, or another bug).  It feels a little weird to be diagnosing rendering issues in a bug on "avoid high memory usage". :)

Comment 5

[Julian Viereck]

Renaming bug and opening new bug that is really about high memory usage.

Comment 6

[Julian Viereck]

From a private email chat with :dholbert :

> So -- I think the rendering difference is just a result of the way we do
print-selection -- we initially print to an infinitely-tall page, which
means percent-heights don't have anything to resolve against.  That's
just the way things work, with our current (imperfect) print-selection
design.
>
> I'm not sure we can "fix" that behavior without completely rewriting the
print-selection code. :-/  That's not to say we shouldn't do that at
some point, but it'd likely be a large undertaking, and probably isn't
likely to be prioritized soon.

Comment 7

[Daniel Holbert [:dholbert]]

Attachment: testcase 2 (just a div w/ %-height)

Here's a more-reduced testcase illustrating comment 3, FWIW.

Comment 8

[Daniel Holbert [:dholbert]]

(Clarifying the bug summary to cover what the testcases here demonstrate)