[Bug 1853937] New: Inconsistent rendering of ti, tt ligatures

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

Bug ID: 1853937
           Summary: Inconsistent rendering of ti, tt ligatures
           Product: Fedora
           Version: 32
            Status: NEW
         Component: lato-fonts
          Assignee: [e-mail]
          Reporter: [e-mail]
        QA Contact: [e-mail]
                CC: [e-mail],
                    [e-mail], [e-mail]
  Target Milestone: ---
    Classification: Fedora

Created attachment 1699956
  --> https://bugzilla.redhat.com/attachment.cgi?id=1699956&action=edit
Sample renderings

The horizontal 't-crossing' strokes of the ti and tt ligatures are rendered
slightly below the x-height, in a manner that is more- or less-visible
depending on font size. It's most visible at 11pt.

Attached are samples rendered with RGB subpixel anti-aliasing, slight hinting.
The issue is visible in the 8, 11 and 14pt samples.

lato-fonts-2.015-9.fc32.noarch
freetype-2.10.1-2.fc32.x86_64

[Bug 1853937] Inconsistent rendering of ti, tt ligatures

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

Alexei Podtelezhnikov  changed:

What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |[e-mail]

--- Comment #1 from Alexei Podtelezhnikov  ---
For completeness sake, please add add "f" and "t" to your images.

[Bug 1853937] Inconsistent rendering of ti, tt ligatures

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

James  changed:

What    |Removed                     |Added
----------------------------------------------------------------------------
         Attachment|0                           |1
        #1699956 is|                            |
           obsolete|                            |

--- Comment #2 from James  ---
Created attachment 1715542
  --> https://bugzilla.redhat.com/attachment.cgi?id=1715542&action=edit
Sample renderings

Updated as requested

[Bug 1853937] Inconsistent rendering of ti, tt ligatures

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

--- Comment #3 from James  ---
(In reply to James from comment #2)
> Created attachment 1715542 [details]
> Sample renderings
>
> Updated as requested

Hold on, ignore those, I had the ligatures turned off...

[Bug 1853937] Inconsistent rendering of ti, tt ligatures

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

James  changed:

What    |Removed                     |Added
----------------------------------------------------------------------------
         Attachment|0                           |1
        #1715542 is|                            |
           obsolete|                            |

--- Comment #4 from James  ---
Created attachment 1715546
  --> https://bugzilla.redhat.com/attachment.cgi?id=1715546&action=edit
sample renderings updated per request

...this time with the ligatures.

[Bug 1853937] Inconsistent rendering of ti, tt ligatures

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

--- Comment #5 from Alexei Podtelezhnikov  ---
Curiously, the ligatures outside of Unicode are the ones loaded without
hinting. Which program is this? I do not see the issue with ftview from
freetype-demos.

[Bug 1853937] Inconsistent rendering of ti, tt ligatures

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

--- Comment #6 from James  ---
The samples are all screenshots from the sample area a Gtk3 font selection box
-- such as you can get e.g. in Gedit.

[Bug 1853937] Inconsistent rendering of ti, tt ligatures

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

--- Comment #7 from Alexei Podtelezhnikov  ---
The glyphs are hinted in the font. It must be Pango which loads them unhinted
(FT_LOAD_NO_HINTING). Please reassign to Pango.

[Bug 1853937] ti, tt ligatures (of at least Lato font) loaded without hinting

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

James  changed:

What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |caillon+fedoraproject@gmail
                   |                            |.com,
                   |                            |[e-mail]
                   |                            |ct.org,
                   |                            |[e-mail]
                   |                            |ct.org,
                   |                            |[e-mail],
                   |                            |[e-mail],
                   |                            |[e-mail],
                   |                            |[e-mail],
                   |                            |[e-mail],
                   |                            |[e-mail],
                   |                            |[e-mail]
          Component|lato-fonts                  |pango
            Summary|Inconsistent rendering of   |ti, tt ligatures (of at
                   |ti, tt ligatures            |least Lato font) loaded
                   |                            |without hinting

[Bug 1853937] ti, tt ligatures (of at least Lato font) loaded without hinting

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

--- Comment #8 from James  ---
(In reply to Alexei Podtelezhnikov from comment #7)
> The glyphs are hinted in the font. It must be Pango which loads them
> unhinted (FT_LOAD_NO_HINTING). Please reassign to Pango.

Done. I've changed the title -- does this accurately summarise the situation?

[Bug 1853937] ti, tt ligatures (of at least Lato font) loaded without hinting

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

James  changed:

What    |Removed                     |Added
----------------------------------------------------------------------------
            Comment|0                           |updated

--- Comment #0 has been edited ---

Created attachment 1699956
  --> https://bugzilla.redhat.com/attachment.cgi?id=1699956&action=edit
Sample renderings

The horizontal 't-crossing' strokes of the ti and tt ligatures are rendered
slightly below the x-height, in a manner that is more- or less-visible
depending on font size. It's most visible at 11pt.

Attached are samples rendered with RGB subpixel anti-aliasing, slight hinting.
The issue is visible in the 8, 11 and 14pt samples.

lato-fonts-2.015-9.fc32.noarch
freetype-2.10.1-2.fc32.x86_64

[Bug 1853937] ti, tt ligatures (of at least Lato font) loaded without hinting

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

Peng Wu  changed:

What    |Removed                     |Added
----------------------------------------------------------------------------
           Doc Type|---                         |If docs needed, set a value

--- Comment #9 from Peng Wu  ---
Could you provide the expected result?

And how do you produce the sample image?

[Bug 1853937] ti, tt ligatures (of at least Lato font) loaded without hinting

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

--- Comment #10 from James  ---
Created attachment 1715700
  --> https://bugzilla.redhat.com/attachment.cgi?id=1715700&action=edit
My fonts.conf

[Bug 1853937] ti, tt ligatures (of at least Lato font) loaded without hinting

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

--- Comment #11 from James  ---
Created attachment 1715702
  --> https://bugzilla.redhat.com/attachment.cgi?id=1715702&action=edit
Large point-size expected result (generated in Inkscape)

[Bug 1853937] ti, tt ligatures (of at least Lato font) loaded without hinting

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

James  changed:

What    |Removed                     |Added
----------------------------------------------------------------------------
         Attachment|sample renderings updated   |Sample renderings in Gtk3
           #1715546|per request                 |font chooser, at 8, 9, 10,
        description|                            |11 and 14 pt

[Bug 1853937] ti, tt ligatures (of at least Lato font) loaded without hinting

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

--- Comment #12 from James  ---
(In reply to Peng Wu from comment #9)
> Could you provide the expected result?
>
> And how do you produce the sample image?

The sample image was produced by taking screenshots from a Gtk3 font chooser.
fonts.conf attached. Using RGB subpixel anti-aliasing with slight hinting.

The expected result is what's seen in the 9pt and 10pt samples: the horizontal
stroke of the ti and tt ligatures lines up with that of a single t. Note in the
8pt, 11pt and 14pt samples the horizonal stroke on the ligature is a pixel or
so below that on the single t.

I've also attached a rendering of "t ti tt" at large point-size rendered in
Inkscape, just to confirm that the glyphs' horizontal strokes do align
geometrically.

[Bug 1853937] ti, tt ligatures (of at least Lato font) loaded without hinting

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

Peng Wu  changed:

What    |Removed                     |Added
----------------------------------------------------------------------------
              Flags|                            |needinfo?([e-mail].u
                   |                            |k)

--- Comment #13 from Peng Wu  ---
Could you use pango-view to produce the actual result?

And use ftview to produce the expected result for comparison.

[Bug 1853937] ti, tt ligatures (of at least Lato font) loaded without hinting

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

--- Comment #14 from Akira TAGOH  ---
easy to reproduce with this:
pango-view --markup -t "<span font_desc='Lato 8'>8pt t ti fi tt</span>^M<span
font_desc='Lato 9'>9pt t ti fi tt</span>^M<span font_desc='Lato 10'>10pt t ti
fi tt</span>^M<span font_desc='Lato 11'>11pt t ti fi tt</span>^M<span
font_desc='Lato 14'>14pt t ti fi tt</span>"

and

ftview -e unic -m "t ti fi tt" -k5 14 /usr/share/fonts/lato/Lato-Regular.ttf

[Bug 1853937] ti, tt ligatures (of at least Lato font) loaded without hinting

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

--- Comment #15 from Akira TAGOH  ---
Created attachment 1720101
  --> https://bugzilla.redhat.com/attachment.cgi?id=1720101&action=edit
Actual result with the helping line

This would demonstorate the issue

[Bug 1853937] ti, tt ligatures (of at least Lato font) loaded without hinting

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

James  changed:

What    |Removed                     |Added
----------------------------------------------------------------------------
              Flags|needinfo?([e-mail].u |
                   |k)                          |

--- Comment #16 from James  ---
Created attachment 1720732
  --> https://bugzilla.redhat.com/attachment.cgi?id=1720732&action=edit
Rendering from pango-view --markup

Provided in part fulfilment of the NEEDINFO. This is with
pango-1.47.0-1.fc33.x86_64.

[Bug 1853937] ti, tt ligatures (of at least Lato font) loaded without hinting

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

--- Comment #17 from James  ---
(In reply to Akira TAGOH from comment #14)
> ftview -e unic -m "t ti fi tt" -k5 14 /usr/share/fonts/lato/Lato-Regular.ttf

When I tried this, it didn't use the ligatures -- not sure how to make them
show up as some of these are non-Unicode ligatures.

[Bug 1853937] ti, tt ligatures (of at least Lato font) loaded without hinting

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

--- Comment #18 from Akira TAGOH  ---
Ah, you're right. I'm not sure even if ftview is capable to render the
ligatures, but how about this then:

hb-view --text "t ti fi tt" /usr/share/fonts/lato/Lato-Regular.ttf

We can confirm it works on harfbuzz layer.

[Bug 1853937] ti, tt ligatures (of at least Lato font) loaded without hinting

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

--- Comment #19 from James  ---
(In reply to Akira TAGOH from comment #18)
> Ah, you're right. I'm not sure even if ftview is capable to render the
> ligatures, but how about this then:
>
> hb-view --text "t ti fi tt" /usr/share/fonts/lato/Lato-Regular.ttf
>
> We can confirm it works on harfbuzz layer.

The renderings from hb-view looks OK to me -- it's difficult to tell because it
seems to be using different font size units to pango-view, and I'm not sure
it's applying the same anti-aliasing and hinting settings.

[Bug 1853937] ti, tt ligatures (of at least Lato font) loaded without hinting

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

--- Comment #20 from Peng Wu  ---
Right, I think we need to use similar settings in hb-view for comparison.

[Bug 1853937] ti, tt ligatures (of at least Lato font) loaded without hinting

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

--- Comment #21 from Peng Wu  ---
It seems this bug is triggered by different hinting style.

I tried with different hinting style like none/medium/full,
the ligatures aligned correctly.

But for hinting style with auto/slight, this bug happens.

Here are the testing command:
$ pango-view --text="t ti fi tt" --hinting=full --font="Lato 8"

[Bug 1853937] ti, tt ligatures (of at least Lato font) loaded without hinting

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

--- Comment #22 from Alexei Podtelezhnikov  ---
Created attachment 1728793
  --> https://bugzilla.redhat.com/attachment.cgi?id=1728793&action=edit
ftview screenshot

(In reply to Peng Wu from comment #21)
> But for hinting style with auto/slight, this bug happens.

I can confirm that FreeType autohinter ignores non-Unicode ligatures, see
attached. Please change the component back to FreeType.

[Bug 1853937] ti, tt ligatures (of at least Lato font) loaded without hinting

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

James  changed:

What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |[e-mail],
                   |                            |[e-mail],
                   |                            |[e-mail]
          Component|pango                       |freetype

[Bug 1853937] Auto-hinter ignores non-unicode ligatures (e.g. Lato ti, tt)

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

James  changed:

What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|ti, tt ligatures (of at     |Auto-hinter ignores
                   |least Lato font) loaded     |non-unicode ligatures (e.g.
                   |without hinting             |Lato ti, tt)

[Bug 1853937] Auto-hinter ignores non-unicode ligatures (e.g. Lato ti, tt)

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

--- Comment #23 from Alexei Podtelezhnikov  ---
Fedora comes with FreeType without HarfBuzz
[https://savannah.nongnu.org/bugs/?59452]. So there is a fix but it is a
circular dependency.

[Bug 1853937] Auto-hinter ignores non-unicode ligatures (e.g. Lato ti, tt)

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

--- Comment #24 from James  ---
(In reply to Alexei Podtelezhnikov from comment #23)
> Fedora comes with FreeType without HarfBuzz
> [https://savannah.nongnu.org/bugs/?59452]. So there is a fix but it is a
> circular dependency.

Understood -- I just rebuild the freetype RPM locally with harfbuzz enabled in
the spec and the ligatures look correct.

[Bug 1853937] Auto-hinter ignores non-unicode ligatures (e.g. Lato ti, tt)

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

--- Comment #25 from James  ---
Couldn't this be worked around by creating a package like freetype-nonharfbuzz
built without HarfBuzz, use that purely as a builddep for the harfbuzz package
in the Fedora buildsystem, and then build a freetype package depending on
harfbuzz?

[Bug 1853937] Auto-hinter ignores non-unicode ligatures (e.g. Lato ti, tt)

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

--- Comment #26 from Akira TAGOH  ---
We may need some tweaks in the spec file to enable bootstrap.
https://docs.fedoraproject.org/en-US/packaging-guidelines/#bootstrapping

[Bug 1853937] Auto-hinter ignores non-unicode ligatures (e.g. Lato ti, tt)

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

Jens Petersen  changed:

What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|unspecified                 |medium

[Bug 1853937] Auto-hinter ignores non-unicode ligatures (e.g. Lato ti, tt)

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

--- Comment #27 from Akira TAGOH  ---
Created a testing package with harfbuzz enabled.

https://copr.fedorainfracloud.org/coprs/tagoh/freetype-harfbuzz/

Indeed, the result of ftview looks good to me.

[Bug 1853937] Auto-hinter ignores non-unicode ligatures (e.g. Lato ti, tt)

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

--- Comment #28 from James  ---
I confirm your SRPM builds for me on Fedora 33 and works as expected.

[Bug 1853937] Auto-hinter ignores non-unicode ligatures (e.g. Lato ti, tt)

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

Jens Petersen  changed:

What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|[e-mail]      |[e-mail]

[Bug 1853937] Auto-hinter ignores non-unicode ligatures (e.g. Lato ti, tt)

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

Akira TAGOH  changed:

What    |Removed                     |Added
----------------------------------------------------------------------------
         Depends On|                            |1906714

Referenced Bugs:

https://bugzilla.redhat.com/show_bug.cgi?id=1906714
[Bug 1906714] Enable OpenType related features with HarfBuzz

[Bug 1853937] Auto-hinter ignores non-unicode ligatures (e.g. Lato ti, tt)

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

Akira TAGOH  changed:

What    |Removed                     |Added
----------------------------------------------------------------------------
            Version|32                          |rawhide

--- Comment #29 from Akira TAGOH  ---
Moving this to rawhide. we are planning to fix this there.

[Bug 1853937] Auto-hinter ignores non-unicode ligatures (e.g. Lato ti, tt)

https://bugzilla.redhat.com/show_bug.cgi?id=1853937
Bug 1853937 depends on bug 1906714, which changed state.

Bug 1906714 Summary: Enable OpenType related features with HarfBuzz
https://bugzilla.redhat.com/show_bug.cgi?id=1906714

What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |CLOSED
         Resolution|---                         |RAWHIDE

[Bug 1853937] Auto-hinter ignores non-unicode ligatures (e.g. Lato ti, tt)

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

Marek Kašík  changed:

What    |Removed                     |Added
----------------------------------------------------------------------------
   Fixed In Version|                            |freetype-2.10.4-3.fc34

--- Comment #30 from Marek Kašík  ---
I've verified that the new freetype with harfbuzz support enabled fixes the
issue. I've used the pango-view command from the comment #14 for that.
I'm closing this.
Thank you all for your help.

[Bug 1853937] Auto-hinter ignores non-unicode ligatures (e.g. Lato ti, tt)

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

--- Comment #32 from James  ---
Seems fixed on my F34 box running freetype-2.10.4-3.fc34.x86_64,
harfbuzz-2.7.4-3.fc34.x86_64 -- OK to close as fixed?

[Bug 1853937] Auto-hinter ignores non-unicode ligatures (e.g. Lato ti, tt)

https://bugzilla.redhat.com/show_bug.cgi?id=1853937

Mohamed El Morabity  changed:

What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |CURRENTRELEASE
             Status|NEW                         |CLOSED
        Last Closed|                            |2021-10-01 17:39:11