1093553 - improve handling of line-height metrics, block ascent, etc., in vertical writing mode

Status: RESOLVED FIXED

(Core :: Layout: Block and Inline, defect)

Description

[Jonathan Kew [:jfkthame]]

We need to tidy up the handling of line-height metrics etc in vertical mode. Using the attached testcase:

* the lines with Latin text are spaced much too widely in vertical mode with sideways-right or mixed orientation, while they're fine in vertical/upright;

* the line with Chinese characters moves horizontally by a substantial distance when switching between upright and sideways display;

* the different sizes of Latin characters are not properly baseline-aligned when displayed with sideways orientation.

Fixing this will provide a better basis for addressing the vertical-align problems (e.g. <sub> and <sup> elements) in bug 1084370.

Comment 1

[Jonathan Kew [:jfkthame]]

A couple of things to do here: we need to be more careful to distinguish when we have a vertical text run from when we're using vertical font metrics; and we need to deal with "inverted" lines (sideways-right text in vertical-lr mode) where the block-dir *ascent* will correspond to the text *descent*.

Comment 2

[Jonathan Kew [:jfkthame]]

Attachment: Improve handling of line-height metrics, block ascent, etc., in vertical writing mode

This makes things a lot better; it renames a bunch of 'vertical' flags to clarify whether they're referring to vertical runs or vertical metrics, and fixes ascent/descent issues. What remains after this patch is that with text-orientation:mixed, the different sizes of Latin text appear centered instead of baseline-aligned. (They're fine in sideways-right mode, where we know the run as a whole should have a dominant alphabetic baseline.)

Comment 3

[Jonathan Kew [:jfkthame]]

Attachment: Testcase for viewing effect of line metrics in various writing modes

Oh, and here's the testcase I intended to attach from the start.

Comment 4

[Jonathan Kew [:jfkthame]]

Attachment: Improve handling of line-height metrics, block ascent, etc., in vertical writing mode

One more thing - with the improved handling of baseline and ascent/descent, we need to make a corresponding fix in nsCaret for the case of "inverted" lines.

Comment 5

[Jonathan Kew [:jfkthame]]

Attachment: Followup to fix positioning of the carent with writing-mode:vertical-lr and text-orientation:sideways-right.

Oops, attached the wrong patch as the "followup". Here it is for real.

Comment 6

[Simon Montagu :smontagu]

Comment on attachment 8516651 [details] [diff] [review]
Improve handling of line-height metrics, block ascent, etc., in vertical writing mode

Review of attachment 8516651 [details] [diff] [review]:
-----------------------------------------------------------------

I think this is OK, though I'm not hugely familiar with all the code you're touching here.

::: layout/base/nsCSSRendering.cpp
@@ +4165,5 @@
>        NS_ERROR("Invalid style value!");
>        return;
>    }
>  
>    // The y position should be set to the middle of the line.

Make the comment here and in the next hunk talk about block direction instead of y

Comment 7

[Jonathan Kew [:jfkthame]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/9e5ac3d61831
https://hg.mozilla.org/integration/mozilla-inbound/rev/acb19a80d5f7

Comment 8

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/9e5ac3d61831
https://hg.mozilla.org/mozilla-central/rev/acb19a80d5f7