Closed Bug 617203 Opened 14 years ago Closed 13 years ago

"First character must be the start of a cluster ..." assertion failure with pango-graphite

Categories

(Core :: Layout: Text and Fonts, defect)

x86_64
Linux
defect
Not set
normal

Tracking

()

RESOLVED FIXED

People

(Reporter: karlt, Assigned: karlt)

Details

(Keywords: regression)

Attachments

(1 file)

http://hg.mozilla.org/mozilla-central/annotate/2b44a6a3bfd8/gfx/thebes/gfxFont.cpp#l3917

When pango-graphite is installed, it adds a PangoEngineLang, which changes the
behavior of pango_break.

The behaviour differs enough that it leads to failed assertions that the first
character of a run begins a cluster, and it is not possible to move the cursor
to the beginning of text if Graphite fonts are used.

This is because Graphite's break does not set is_cursor_position for the
position before the first character.

STR:

1. Install pango-graphite and Dai Banna SIL Book
   http://scripts.sil.org/DaiBannaSIL

2. Copy 'ᦎᦷ ᦑᦺ' to the search bar.
   See assertion failures (with debug builds).

3. Try to use arrow keys to move cursor to beginning of the text.
   Fail.
I suspect assertions would fail even in very old builds.
The cursor behavior is a regression since 2010-10-14.
Keywords: regression
I'm tempted to blacklist GraphiteEngineLang because it claims support for
multiple scripts, but, for non-graphite fonts (Engine selection is not
font-dependent), it merely runs the basic pango_default_break, overriding
script-specific Engines - and it runs pango_default_break twice.
See graphite_engine_break at
http://scripts.sil.org/svn-public/graphite/graphite/trunk/wrappers/pangographite/silgraphite-break.c

However, I think it is a bug in our code to rely on specific behavior from
pango_break, and we should fix that.
http://hg.mozilla.org/mozilla-central/annotate/2b44a6a3bfd8/gfx/thebes/gfxPangoFonts.cpp#l2571
Assignee: nobody → karlt
Attachment #495735 - Flags: review?(jfkthame)
With the improvements we've made to gfxPlatform::SetupClusterBoundaries() (see bug 553981), do we really still need to be calling pango_break here, or could we remove the static SetupClusterBoundaries function from the gfxPangoFonts.cpp code altogether (thereby resolving both this and bug 614476)?
We now only call pango_break (this static SetupClusterBoundaries()) when using Pango for shaping.

Pango's indic PangoEngineLangs has some special breaking rules that I assume gfxPlatform::SetupClusterBoundaries() does not handle, and it seems appropriate to use pango_break when using pango_shape (as I assume we do for indic scripts).
This code was removed in bug 703100.
Status: ASSIGNED → RESOLVED
Closed: 13 years ago
Resolution: --- → FIXED
Attachment #495735 - Flags: review?(jfkthame)
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