156881 - (text-decoration-mode) Underline should skip character/part-of-character that is below the base line (text-decoration-mode)

Status: RESOLVED WONTFIX

(Core :: Layout, enhancement)

Description

[Arthit Suriyawongkul]

From Bugzilla Helper:
User-Agent: Mozilla/5.0 (X11; U; SunOS sun4u; en-US; rv:1.0rc3) Gecko/20020614
Netscape/7.0b1
BuildID:    20020614


<u>&#3585;&#3586;&#3629;&#3640;&#3629;&#3641;&#3629;&#3642;&#3597;&#3600;&#3598;&#3599;&#3620;&#3622;&#3585;&#3586;</u>

in Thai text,
we need the line to skip all below-level part & tail of char
(also below-level char, like below vowel)

please see the attached testcase.


Reproducible: Always
Steps to Reproduce:
open attached testcase

Actual Results:
underline went across Thai base-level characters, also base-level part/tail of
Thai characters.

Expected Results:
underline skip Thai base-level characters, also base-level part/tail of Thai
characters.

----

also, in case of English text, e.g

 abcgyqjabc

when it went underlined,
should the line skip tails of "gyqj" ?

Comment 1

[Arthit Suriyawongkul]

Attachment: Thai underlined text

Comment 2

[Arthit Suriyawongkul]

FYI,
Thai character has 4 levels of displaying.
from highest to lowest level:
 top
 above (same level as accent mark of western)
 base  (same level as general western character)
 below


list of below-level Thai character:
U+0E38
U+0E39
U+0E3A

list of Thai character with "below-level part":
U+0E0D
U+0E10

list of Thai character with "below-level tail":
U+0E0E
U+0E0F
U+0E24
U+0E26
U+0E45
U+0E46

Comment 3

[Arthit Suriyawongkul]

some character like U+0E3A,
will be unseen if the underline striked over it.

Comment 4

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

This is, IMO, another deficiency of the underline definition in the CSS spec
(which we're moving towards in bug 1777), that we're not allowed to do this. 
(Or are we?)

Comment 5

[Arthit Suriyawongkul]

propose new attribute to CSS ?
to let web developer able to choose style for underline ?

2 style options
 - strike out
 - skip over

seems this too hard -_-'
just my 2 satangs :|

Comment 6

[Arthit Suriyawongkul]

(changed the summary to be more general)

example of Latin characters that has some part below the base line:

U+0067  g
U+006A  j
U+0070  p
U+0071  q
U+0079  y
U+00C7  Latin Capital Letter C with Cedilla
U+00FD  Latin Small Letter Y with Acute
U+00FE  Latin Small Letter Thorn
U+0104  Latin Capital Letter A with Ogonek
U+014B  Latin Small Letter Eng

Comment 7

[Arthit Suriyawongkul]

comment #5 .. may be it's not clear.

possible options
1) not skip
2) skip only whitespace
3) skip only below-base-line part-of-character
4) skip whitespace and below-base-line part-of-character

Comment 8

[Hixie (not reading bugmail)]

I think we are allowed to do this per the spec, actually. It counts the same as
changing the thickness to allow for subscripts, which the spec explicitly allows.

We should give feedback to the CSSWG that we want 'text-underline-mode' to have
a value which controls whether or not we skip descenders.

Comment 9

[Arthit Suriyawongkul]

actually, i've sent an e-mail to [e-mail] yesterday,
not sure if it a good place to send to.
(i'm not subscribed to the list yet, so the msg may delayed)

i can fwd the e-mail to you on monday morning,
when i'm at the office and can access the sentbox :)

please comment on it, thanks.

Comment 10

[Arthit Suriyawongkul]

list archive
http://lists.w3.org/Archives/Public/www-style/

Comment 11

[Prabhat Hegde]

Attachment: Hindi underlining example

Shows input and output sequences and expected underlining. Pl ignore the boxes.


prabhat

Comment 12

[Prabhat Hegde]

Comment about attachment 92925 [details]
Indian language scripts (particularly South Indian languages) will have the same
issue. In addition could someone point me to the logic of underlining text? My
concern is that CTL (Complex Text Layout) scripts such as Thai, Hebrew, Arabic
require underlining to happen after the characters are shaped to account for
shaping as well as below-base characters. Pl see attached gif for hindi.
prabhat

Comment 13

[Arthit Suriyawongkul]

Attachment: example of different underlining styles, using Thai/Latin text

black: grapheme cluster WITH some part below the base line level.
grey: grapheme cluster without.

Comment 14

[Arthit Suriyawongkul]

from attachment 94217 [details]
i think "skip-whole-cell" is the easiest to implement.
(note: i use the word (display) cell/grapheme cluster interchangably here .. sorry)

Comment 15

[Boris Zbarsky [:bzbarsky]]

So if I have:

<span style="text-decoration: underline">
  <span style="vertical-align: -0.5em">text</span>
  more text
</span>

what should happen?  Should the same apply for overline and ascenders?  (Think
bigger font in the middle of an overlined inline.)

Comment 16

[Hixie (not reading bugmail)]

http://www.w3.org/TR/css3-text/#text-decoration-mode

Comment 17

[Arthit Suriyawongkul]

Similar issue in OpenOffice.org 

Underlining should optionally skip descenders and characters below baseline
http://www.openoffice.org/issues/show_bug.cgi?id=43776

Comment 18

[Justin Kerk]

Isn't this a dupe of bug 64874?

Comment 19

[fantasai]

*** Bug 64874 has been marked as a duplicate of this bug. ***

Comment 20

[Disorn Homchuenchom]

Attachment: Message: Jiggy says “สูงสุดคืนสู่สามัญ”

The problem still affects with current nightly build.

Comment 21

[Arthit Suriyawongkul]

BugAThon Bangkok:

We all agreed that this bug is not a blocking bug for Thai support.
(i.e. just optional, good to have, but not necessary)

Comment 22

[WulfTheSaxon [:Wulf]]

This seems more important with the new support for colored underlines.

Comment 23

[Jeff Muizelaar [:jrmuizel]]

I have a very rough idea of how to do this. If someone's interested in trying to fix it I can give some guidance. It would be good to prototype out an algorithm for breaking the underline first.

Comment 24

[u467816]

I would like to work on this bug, i am good at c++. Please guide me through this

Comment 25

[fantasai]

Aish, you should probably look over the CSS3 Text Decoration spec:
  http://www.w3.org/TR/css-text-decor-3/
and maybe ping jrmuizel directly -- he seems to have not noticed your comment. :)

Comment 26

[Xidorn Quan [:xidorn] UTC+10]

It looks like this property has been removed from specs long ago. I cannot find it in any current draft. So close it.

Comment 27

[Jeff Muizelaar [:jrmuizel]]

Bug 812990 supersedes this.