Note: There are a few cases of duplicates in user autocompletion which are being worked on.

update margin collapsing to slight rule change

ASSIGNED
Assigned to

Status

()

Core
Layout: Block and Inline
ASSIGNED
10 years ago
6 years ago

People

(Reporter: dbaron, Assigned: fantasai)

Tracking

(Depends on: 1 bug, Blocks: 1 bug)

Trunk
Points:
---
Dependency tree / graph
Bug Flags:
wanted-next +
blocking1.9 -
wanted1.9 -

Firefox Tracking Flags

(Not tracked)

Details

(Whiteboard: [not-ready-for-cedar], URL)

Attachments

(1 attachment)

(Reporter)

Description

10 years ago
There's a slight change to the margin collapsing rules in http://lists.w3.org/Archives/Member/w3c-css-wg/2007JanMar/0535.html that's been accepted for the next draft of CSS2.1.  We should implement this.

Steps to reproduce:
 load http://dbaron.org/css/test/2007/0329-blog-examples/1

Actual results:
 hello is the same distance below the blue block as A is above it

Expected results:
 there should be a gap between hello and the blue block so hello is 50px below A
Flags: blocking1.9?
(Reporter)

Updated

10 years ago
Flags: blocking1.9? → blocking1.9-
Whiteboard: [wanted-1.9]
(Assignee)

Comment 1

10 years ago
Created attachment 262698 [details] [diff] [review]
suggested patch

I'm pretty sure that conditional fixes the bug. I'm less sure about whether it's the right place to put the conditional.
Assignee: nobody → fantasai.bugs
Status: NEW → ASSIGNED
Attachment #262698 - Flags: review?(dbaron)
(Assignee)

Comment 2

10 years ago
My build still passes http://www.hixie.ch/tests/adhoc/css/box/block/margin-collapse/microsoft/all.html with flying colors (except 005.html, of course, since the test is now wrong). I also ran the reftests and nothing new failed.
I probably should be the reviewer...

Shouldn't the fix be after "clearance = aState.mY - (currentY + topMargin);"?

+      clearance -= clearance + incomingMargin.get();

This is equivalent to "clearance = -incomingMargin.get();" Can you explain why this is correct? I don't see it. I think it would be better if we explicitly did the calculation described in Hixie's email.
(Assignee)

Comment 4

10 years ago
> Shouldn't the fix be after "clearance = aState.mY - (currentY + topMargin);"?

That's where I thought it should go, but it didn't work there. I spent hours trying to figure out why, but my programming fu wasn't strong enough. Even setting clearance to random numbers there didn't break my testcases. -__-;; I don't understand at all.

> Can you explain why this is correct?

I can try to explain why I *think* it's correct...

The point of the spec fix is that clearance should never move an element *up*.
It only moves an element up if it's negative, hence the check for negativeness.
It also only moves the element up if it winds up overcompensating for the hypothetical margin collapse. The margin can't collapse more than the amount of the previous margin, so if the magnitude of negative clearance is more than that, then it's overcompensating, and it's overcompensating by
  |clearance| - incomingMargin
which, given that clearance is negative, is the same as
  clearance + incomingMargin
Subtract out the overcompensation, and the element no longer moves up.

That's my logic. Hyatt thinks its wrong, so maybe I'm missing something important here. Hence "suggested patch" rather than "proposed patch" and a request for dbaron's review since he's more of a margin collapsing guru than I am.
(Assignee)

Comment 5

10 years ago
Note that, if my logic serves me correctly, if a negative margin is one (or both) of two margins collapsing, then the amount of the collapse must be non-negative. A  negative margin collapsing with a positive one is the sum of the two (no difference if they collapse or don't collapse), and two negative margins collapsing are the max of the two, i.e. the difference between not collapsing and collapsing is positive. Therefore (correct me if I'm wrong) clearance is only negative if it's compensating for a positive-positive collapse.
Flags: wanted1.9+
Whiteboard: [wanted-1.9]
Flags: wanted1.9-
Flags: wanted1.9+
Flags: wanted-next+
(Reporter)

Updated

9 years ago
Attachment #262698 - Flags: review?(dbaron) → review?(roc)
(Reporter)

Comment 6

9 years ago
Comment on attachment 262698 [details] [diff] [review]
suggested patch

I should have transferred this review request ages ago.
Comment on attachment 262698 [details] [diff] [review]
suggested patch

I kinda forgot about this. I think it's right, though.

We should have a reftest.
Attachment #262698 - Flags: review?(roc) → review+
(Reporter)

Comment 8

7 years ago
And updated version of this patch is:
http://hg.mozilla.org/users/dbaron_mozilla.com/patches/raw-file/7c922ff64911/clearance-should-not-move-up
and it fixes our handling of the following tests in the CSS 2.1 test suite:
http://test.csswg.org/suites/css2.1/20101027/html4/margin-collapse-clear-005.htm
http://test.csswg.org/suites/css2.1/20101027/html4/margin-collapse-clear-011.htm
Blocks: 605520
Do you want to land it for FF4?
(Reporter)

Comment 10

7 years ago
I tend to think not; I'd rather land it afterwards.

Also see:
http://lists.w3.org/Archives/Public/public-css-testsuite/2010Nov/0124.html
(Assignee)

Comment 11

7 years ago
I'll note that the CSS2.1 spec could get blocked on whether this fix breaks web compat, and currently only Mozilla seems capable of figuring that out within the next year or two.

Updated

7 years ago
Depends on: 610267
(Reporter)

Comment 12

7 years ago
This seems to break Acid2.
(Reporter)

Comment 13

7 years ago
This also fixes http://test.csswg.org/suites/css2.1/20110111/html4/margin-collapse-164.htm
(Reporter)

Comment 14

7 years ago
So apparently:
 * the IE folks say fixing this breaks some sites
 * the tests are actually invalid, although only unintentionally so, since "hypothetical position" is defined **relative to the parent**

So it sounds like we might fix the tests.
(Reporter)

Comment 15

7 years ago
Though http://lists.w3.org/Archives/Member/w3c-css-wg/2007JanMar/0514.html shows that the explicit intent of the discussion was to fix the test that has now become http://test.csswg.org/suites/css2.1/20101027/html4/margin-collapse-clear-005.htm

Comment 16

6 years ago
Sounds like this patch is not ok to go on m-c, right?  If I'm wrong, please let me know!
Whiteboard: [not-ready-for-cedar]

Updated

6 years ago
Depends on: 50959
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