https://issues.apache.org/bugzilla/show_bug.cgi?id=53573

--- Comment #2 from na...@th.ibm.com ---
Thanks for the promptly reply.
Yes, i have tested with FOP 1.0 and it product exactly the same as the first
line of the picture i attached.

There are few Thai fonts that aren't using GSUB and GPOS.
Those few deploy a default glyph position that will never collide with other
glyph. However, it gave a result with problem that call "floating tone mark".
These few fonts also leave the glyph determination work to LayoutEngine.
It expects LayoutEngine to pick correct glyph by itself. In order to accomplish
this, it need State Machine. You can take a peek at ICU4C LayoutEngine. There
is a ThaiLayoutEngine there. However, ICU4J doesn't have one.

Note:
1. In order to avoid GSUB and GPOS it require the font to use Unicode PVA.
Adobe recommends to avoid it as it is non-standard. The best example of problem
is ICU4C uses different code point compare to Adobe that assign to Thai
glyph.ICU gives more correct result.
2. All known Thai fonts in MS.Windows use GSUB and GPOS except Arial Unicode.
3. All known True Type fonts in Linux use GSUB and GPOS.

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