[webkit-dev] Ruby Text Enhancements

[Eric Mader]

On Sep 20, 2010, at 9:52 PM, Roland Steiner wrote:

> Great to see someone else interested in doing ruby implementation! :) 
> 
> I did the original ruby implementation, so I'm very happy to help with any questions/problems/issues (bugs? there are not bugs!). BTW, please note that there is another ruby patch in the review pipeline: https://bugs.webkit.org/show_bug.cgi?id=41040 (had to modify and re-submit this one after in-flight clashes with another patch) that might affect the implementation.
> 
> On Tue, Sep 21, 2010 at 3:12 AM, David Hyatt <hyatt at apple.com> wrote:
> On Sep 17, 2010, at 8:07 PM, Eric Mader wrote:
> 
> > Hi,
> >
> > I'm working on making the following enhancements to Ruby Text:
> >
> > 1) Implement the behavior of ruby-overhang:auto
> 
> Oh vey, that's ambituous! :)  There's so many corner cases I foresee on this one that I was just too happy to postpone it when we originally discussed to leave out CSS3 ruby stuff from the initial implementation, which is purely based off HTML5 - including supporting multiple base/text pairs within a single ruby, and line-breaking within the ruby.

Yes, it's a bit scary. ;-) I don't think I could implement the whole thing at once, so I'm looking at doing a partial implementation. Maybe the first round would only check to be sure that the neighboring blocks aren't <ruby> blocks.

I'm looking at using a RenderOverflow object to implement this. Can you point me at any documentation for this class, other than what's in the code? I'm having some trouble sorting out what all the various rectangles used in conjunction with this object represent.

> > 2) implement the behavior of ruby-line-stacking:exclude-ruby
> 
> Which way do you intend to implement this? AFAICT the current consensus seems to go towards having ruby included by default rather than excluded.

Well, the spec. says that exclude-ruby is the default. Looking at a few example sites, it seems that they don't use big enough inter-line spacing to accommodate ruby text, so changing the exclude-ruby as the default would result in the ruby overlapping the previous line, which is probably worse than the current state where the inter-line spacing isn't uniform. (using 60% as the default size for ruby text probably makes this a bit worse)

As ruby implementations with the specified default implemented become more common, I expect that sites will be updated to use correct inter-line spacing and everyone will be happy. In the near-term, though, things will look worse if we implement the default...

> > 3) Add some Mac OS specific character properties to the ruby text
> >
> > 4) Turn off the underline when the ruby text is in a link
> >
> > I've looked at the code enough to know that the layout or ruby text is done by the normal block stacking in BlockLayout. I'm guessing that I can do at lest the first two tasks by changing the RenderRuby code to report a different width and / or height for the ruby block. Does this seem like the right way to do what I want?
> >
> > Assuming for the moment that it is, I have some questions:
> >
> > 1) What methods should I subclass to report the adjusted width and height?
> >
> 
> I'm very hazy on the Ruby implementation.  I believe it makes an inline-block with two block children vertically stacked, and then it uses text-align:center to center the ruby base.  If so, this behavior has to be preserved when the ruby text is wider than the base.
> 
> Yes, that's the basic layout for a single ruby text/base pair. Note that multiple such pairs may be contained within a single <ruby> element (which is normally an inline element, unless it's floated or positioned). A <ruby> may also include renderers for :before and :after content, which are outside of the inline-blocks for base/text pairs. This is implemented in the aforementioned patch for 41040, which also fixes some issues with RenderRubyAsBlock and supersedes the patch for 43722).
>  
> I think a reasonable way to implement overhang therefore would be with negative margins applied to the ruby run.  This way the correct layout of the Ruby object is preserved, and the surrounding text will just naturally get pushed inside the Ruby object to overlap it.
> 
> Basically you can compare the delta in width between the base and the text and then apply margins to either side of the ruby run based off how you want to overhang.
> 
> That's also what I'd suggest. However, there are the following additional things to consider:

See my comments about RenderOverflow above. Is that the right way to go? Do I set the width of the <ruby> block to the width of the base text, or to the width of the ruby text and then give it the appropriate margins?

> 
> > About turning off the underline if the ruby is in a link: I've looked at the styles and tried adding code to change the parts that I think relate to this, but haven't found anything that makes a difference. It's also occurred to me that I might be able to do this by writing a rule in <WebKit>WebCore/css/html.css, but I can't figure out exactly what the rule would look like. I tried adding "text-decoration: none" to the "ruby > rt" section, but that doesn't do it.
> >
> > (at first, I thought that is was probably overkill, but now I think that turning text-decoration off for all ruby text is probably right.)
> 
> There is no way to do this.  The closest I see is:
> 
> http://dev.w3.org/csswg/css3-text/#text-decoration-skip
>  
> This is not implemented in WebKit yet.
> 
> We'd probably need to add a new value to that property if Ruby is supposed to be skipped.
> 
> Ergh.... Looking at it, I'm not sure that's a good proposal at all - at least it has still lots to address (it doesn't address list bullets, or :before/:after generated content, for one). I think that the best approach for ruby would be to view the whole ruby run (i.e., base and text combined) as the main object for text-decoration, and not the base and text individually. That is:
> 
> .) underline: line painted below the base only, over the width of base and text (but excluding any overhangs!)
> .) overline: overline painted above the text, same as above - note that the line width doesn't (!) change
> .) line-through: either just the base is decorated, or both base and text. I can see arguments for either way, although I think painting a line-through through the text may overly obscure it, since it's quite small - note that the line width for the ruby text would need to be different in this case as well, which in turn probably means amending the spec.
> .) blink: all blinks ;)
> 
> This however means that a rule for <rt> would need to affect the ruby text separately, independent of the decoration of the whole thing (which IMHO would be a good thing anyway).

I'm inclined to skip this one for now. Too many cans of worms open already. ;-)

> Cheers,
> 
> - Roland

Regards,
Eric


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