[Libreoffice-bugs] [Bug 141418] New: Allow derivative styles to maintain x-height or M-height

[bugzilla-daemon at bugs.documentfoundation.org]

https://bugs.documentfoundation.org/show_bug.cgi?id=141418

            Bug ID: 141418
           Summary: Allow derivative styles to maintain x-height or
                    M-height
           Product: LibreOffice
           Version: 7.1.1.2 release
          Hardware: All
                OS: All
            Status: UNCONFIRMED
          Severity: normal
          Priority: medium
         Component: LibreOffice
          Assignee: libreoffice-bugs at lists.freedesktop.org
          Reporter: eyalroz1 at gmx.com

Created attachment 170888
  --> https://bugs.documentfoundation.org/attachment.cgi?id=170888&action=edit
Same font size, different character heights

The customary measure of font size is actually a rather complex voodoo which
doesn't tell the user much. At best, it is close to being "somewhere between
1/0.7 and 1/0.6 of the Em-height". See discussion here:

https://graphicdesign.stackexchange.com/questions/4035/what-does-the-size-of-the-font-translate-to-exactly

or here:

https://www.thomasphinney.com/2011/03/point-size/

In LO writer (and all of LO) font dialogs, sizes are given in terms of this
inscrutable font size. And if you create a style derived from another style, it
will maintain the same "size" - but not necessarily the same Em-height nor
x-height.

This is problematic in running (Latin) text, where most characters are
lowercase, and their height is basically the x-height. Now, if you use
character styles with different fonts in the same text run, and fail to
carefully set their font size (possibly even to a non-integral value), the
sizes of different parts of the run will vary, distracting the user.

This is not some esoteric use case: You just:

1. Create a new document in LO writer.
2. Write some text, say "foo bar"
3. Select "bar"
4. Change the character style (not the paragraph style!) to "Source Text"

You'll see a significant character height difference. (Actually, this might
depend on your font selection, but it would work with most default choices, and
particularly with Liberation Serif vs Liberation Mono.) The attached document
illustrates this.

This also happens when your concern is the M-height:

1. Create a new document in LO writer.
2. Write some text, say "foo bar"
3. Select "foo"
4. Set the font family to Liberation Serif
5. Select "bar"
6. Set the font family to Lucida Sans Unicode (available from here if you don't
have it: https://www.wfonts.com/font/lucida-sans-unicode )

You'll again notice a significant difference height difference.

It would be useful (perhaps one might even say: necessary), if it were possible
for derivative styles to track the x-height (or M-height) of the underlying
style rather than its M-height.

This can be achieved in one of several ways - partially depending on the extent
to which there is an interest in exposing these height figures to users. I'm
mulling over opening a separate bug about that.

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