Improve fallback for Burmese with leading punctuation + spacing mark

Improve fallback for Burmese with leading punctuation + spacing mark

Issue 618178 describes an example where a Burmese text run starts with a
leading punctuation character followed by a combining spacing mark. This
grapheme cannot be shaped with the default font, since Times for example
cannot display the combination of a left quote with a Burmese combining
mark. Our fallback code attempts to find a fallback font based on the
first character at the beginning of an extracted unshaped sub-run, which
does not lead to finding a font suitable for Myanmar text in this case.
So in a way it runs into a fallback trap, where no fallback hint helps
to find the right fallback font and the whole run ends up as notdef
glyphs.

This CL attempts to resolve this by looking for a better fallback hint
character, which is not script common or inherited, if such is
available. This improves the situation for the Burmese text from the
issue report.

In addition, as a better fix we should give higher importance to the
locale information in font fallback, filed as issue 668706.

BUG=618178
R=eae,kojii,behdad

Committed: https://crrev.com/d9280a5e951415e1b2c6c7958adda19b731a99fa
Cr-Commit-Position: refs/heads/master@{#434665}

[drott, 2016-11-25 13:54:59]

The CQ bit was checked by drott@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-11-25 13:55:11]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[drott, 2016-11-25 13:56:45]

Description was changed from

==========
Improve fallback for Burmese with leading punctuation + spacing mark

Issue 618178 describes an example where a Burmese text run starts with a
leading punctuation character followed by a combining spacing mark. This
grapheme cannot be shaped with the default font, since Times for example
cannot display the combination of a left quote with a Burmese combining
mark. Our fallback code attempts to find a fallback font based on the
first character at the beginning of an extracted unshaped sub-run, which
does not lead to finding a font suitable for Myanmar text in this case.
So in a way it runs into a fallback trap, where no fallback hint helps
to find the right fallback font and the whole run ends up as notdef
glyphs.

This CL attempts to resolve this by looking for a better fallback hint
character, which is not script common or inherited, if such is
available. This improves the situation for the Burmese text from the
issue report.

In addition, as a better we should give higher importance to the locale
information in font fallback, filed as issue 668706.

BUG=618178
R=eae,kojii,behdad
==========

to

==========
Improve fallback for Burmese with leading punctuation + spacing mark

Issue 618178 describes an example where a Burmese text run starts with a
leading punctuation character followed by a combining spacing mark. This
grapheme cannot be shaped with the default font, since Times for example
cannot display the combination of a left quote with a Burmese combining
mark. Our fallback code attempts to find a fallback font based on the
first character at the beginning of an extracted unshaped sub-run, which
does not lead to finding a font suitable for Myanmar text in this case.
So in a way it runs into a fallback trap, where no fallback hint helps
to find the right fallback font and the whole run ends up as notdef
glyphs.

This CL attempts to resolve this by looking for a better fallback hint
character, which is not script common or inherited, if such is
available. This improves the situation for the Burmese text from the
issue report.

In addition, as a better fix we should give higher importance to the 
locale information in font fallback, filed as issue 668706.

BUG=618178
R=eae,kojii,behdad
==========

[drott, 2016-11-25 13:57:02]

PTAL, feedback welcome on the general approach.

[commit-bot: I haz the power, 2016-11-25 15:24:04]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-11-25 15:24:05]

Dry run: Try jobs failed on following builders:
  win_chromium_rel_ng on master.tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel_...)

[eae, 2016-11-25 16:39:59]

Seems like a reasonable approach, let's give it a try and adjust as needed.

LGTM

Thanks for working on this!

[drott, 2016-11-28 11:06:54]

The CQ bit was checked by drott@chromium.org

[drott, 2016-11-28 11:06:54]

The patchset sent to the CQ was uploaded after l-g-t-m from eae@chromium.org
Link to the patchset: https://codereview.chromium.org/2530153002/#ps20001
(title: "Baselines for platforms where test is run")

[commit-bot: I haz the power, 2016-11-28 11:07:07]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-11-28 14:07:47]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-11-28 14:07:48]

Try jobs failed on following builders:
  win_chromium_rel_ng on master.tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel_...)

[drott, 2016-11-28 15:12:50]

Reintroduce null hint check

[drott, 2016-11-28 15:12:58]

The CQ bit was checked by drott@chromium.org

[drott, 2016-11-28 15:12:59]

The patchset sent to the CQ was uploaded after l-g-t-m from eae@chromium.org
Link to the patchset: https://codereview.chromium.org/2530153002/#ps30009
(title: "Reintroduce null hint check")

[commit-bot: I haz the power, 2016-11-28 15:13:13]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-11-28 16:35:24]

CQ is committing da patch.

Bot data: {"patchset_id": 30009, "attempt_start_ts": 1480345978531700,
"parent_rev": "52d523d9f6e08212f55359d13ed41f71091587b5", "commit_rev":
"62a0e47378ad6a118c922eb7b86576d4decdab0c"}

[commit-bot: I haz the power, 2016-11-28 16:35:51]

Committed patchset #3 (id:30009)

[commit-bot: I haz the power, 2016-11-28 16:38:15]

Description was changed from

==========
Improve fallback for Burmese with leading punctuation + spacing mark

Issue 618178 describes an example where a Burmese text run starts with a
leading punctuation character followed by a combining spacing mark. This
grapheme cannot be shaped with the default font, since Times for example
cannot display the combination of a left quote with a Burmese combining
mark. Our fallback code attempts to find a fallback font based on the
first character at the beginning of an extracted unshaped sub-run, which
does not lead to finding a font suitable for Myanmar text in this case.
So in a way it runs into a fallback trap, where no fallback hint helps
to find the right fallback font and the whole run ends up as notdef
glyphs.

This CL attempts to resolve this by looking for a better fallback hint
character, which is not script common or inherited, if such is
available. This improves the situation for the Burmese text from the
issue report.

In addition, as a better fix we should give higher importance to the 
locale information in font fallback, filed as issue 668706.

BUG=618178
R=eae,kojii,behdad
==========

to

==========
Improve fallback for Burmese with leading punctuation + spacing mark

Issue 618178 describes an example where a Burmese text run starts with a
leading punctuation character followed by a combining spacing mark. This
grapheme cannot be shaped with the default font, since Times for example
cannot display the combination of a left quote with a Burmese combining
mark. Our fallback code attempts to find a fallback font based on the
first character at the beginning of an extracted unshaped sub-run, which
does not lead to finding a font suitable for Myanmar text in this case.
So in a way it runs into a fallback trap, where no fallback hint helps
to find the right fallback font and the whole run ends up as notdef
glyphs.

This CL attempts to resolve this by looking for a better fallback hint
character, which is not script common or inherited, if such is
available. This improves the situation for the Burmese text from the
issue report.

In addition, as a better fix we should give higher importance to the
locale information in font fallback, filed as issue 668706.

BUG=618178
R=eae,kojii,behdad

Committed: https://crrev.com/d9280a5e951415e1b2c6c7958adda19b731a99fa
Cr-Commit-Position: refs/heads/master@{#434665}
==========

[commit-bot: I haz the power, 2016-11-28 16:38:16]

Patchset 3 (id:??) landed as
https://crrev.com/d9280a5e951415e1b2c6c7958adda19b731a99fa
Cr-Commit-Position: refs/heads/master@{#434665}

[Marijn Kruisselbrink, 2016-11-28 21:06:54]

A revert of this CL (patchset #3 id:30009) has been created in
https://codereview.chromium.org/2532253002/ by mek@chromium.org.

The reason for reverting is: This seems to be causing test failures for
fast/text/international/text-spliced-font.html on
https://build.chromium.org/p/chromium.webkit/builders/WebKit%20Win10/builds/1....

[kojii, 2016-11-29 09:26:48]

lgtm