Closed Bug 654167 Opened 13 years ago Closed 13 years ago

1px double borders not painting at all with border-collapse:collapse


(Core :: Layout: Tables, defect, P2)

Windows XP





(Reporter: pgrosso, Assigned: bzbarsky)





(2 files)

User-Agent:       Mozilla/5.0 (Windows NT 5.1; rv:2.0.1) Gecko/20100101 Firefox/4.0.1
Build Identifier: Firefox 4.0.1 ("up to date" as of 2011 May 2)

Using the collapsing border model in tables, I am not always getting the border conflict resolution behavior I expect.  The page at is self-documenting and contains more details.

Reproducible: Always

Actual Results:  

Expected Results:  
So the issue here is that in the collapsed border model a 1px wide "double" border is not showing up, right?  That probably has to do with the fact that painting a 1.33px wide "double" (which really needs at least 3px to show up) border  _exactly_ on top of a pixel boundary doesn't work very well, not with border conflict resolution...  In the separated border case, the drawing code is different, and the border is positioned on top of a pixel, not on top of a boundary, so things work out better.

We should probably just treat "double" borders thinner than 3px as solid in the table BC drawing code.
Perhaps that is the crux of the issue, because when I made its style solid (or dashed, etc.), it does show.  In which case it isn't a conflict resolution issue.  I was misled when the separated border case showed the 1pt double rule properly (I was not aware that the drawing code is different in that case).  Thanks for the response.
But now compare and which are identical except the second has an extra global CSS rule setting border style to none for the top and left rules on hd and th.  In the first case, the top rules for the third and fourth table are black, not red as I would have expected.  It looks like the default th, td border style is 1.5pt, black, solid, so that the default is taking precedence over a specified solid rules unless what's specified is at least 1.5pt wide.
> It looks like the default th, td border style is 1.5pt, black, solid

The default styles if you specify rules="none" are the ones in bug 648531 comment 2.  Those include "border-width: thin", which should be 1px wide.  The border-collapse code converts all widths into integer pixel widths before doing conflict resolution (which is arguably a bug) and it looks like it does so by truncating, not rounding (another bug).  1pt is 1.333333px.  So 2px is 1.5pt, and hence any value smaller than 1.5pt will be truncated to 1px.  And then the thin border is the same width and it wins because of rule 4 in border conflict resolution.

Worth checking whether the bugs about comparing after conversion to integer pixels and the fact that the conversion truncates instead of rounding are filed; if not, we should get them on file.  But we should definitely fix the painting issue.
Ever confirmed: true
Summary: Table border conflict resolution is not working as I expect → Thin 1px double borders not painting at all with border-collapse:collapse
Here's the problem in nsCSSRendering::DrawTableBorderSegment :

    if ((aBorder.width > 2) && (aBorder.height > 2)) {

Except aBorder is in app units (so 1px is 60, not 1).

Fix coming up once I figure out when this broke.
Assignee: nobody → bzbarsky
Looks like this has been broken at least back to Firefox 3.0.  Gotta love lack of tests...
And broken in Firefox 2 as well.  I'm going to stop worrying about this!
This might just be broken back to bug 41262 or earlier.  Anyway, patch coming up.
Priority: -- → P2
Summary: Thin 1px double borders not painting at all with border-collapse:collapse → 1px double borders not painting at all with border-collapse:collapse
Whiteboard: [need review]
Oops.  I should have searched for existing bugs.  :(
Comment on attachment 529563 [details] [diff] [review]
Fix drawing of thin 'border-style: double' border-collapsed borders.

Review of attachment 529563 [details] [diff] [review]:
Attachment #529563 - Flags: review?(roc) → review+
Whiteboard: [need review] → [need landing]
Closed: 13 years ago
Flags: in-testsuite+
Resolution: --- → FIXED
Whiteboard: [need landing]
Target Milestone: --- → mozilla6
Mozilla/5.0 (Windows NT 5.1; rv:6.0) Gecko/20100101 Firefox/6.0

Verified issue on Windows XP, Windows 7, Mac OS X 10.6 and Ubuntu using the page from Comment 0 ( and the test case attached in Comment 5.

Setting resolution to VERIFIED FIXED.
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