RE: composition text property

["Drew Adams" <drew.adams@oracle.com>]

Trying again - got no reply. Anybody know about the `composition' property?
Thx.

> From: Drew Adams Sent: Wednesday, May 30, 2007 9:09 AM
> From the Elisp manual, node Special Properties, `composition':
>
>      This text property is used to display a sequence of characters as a
>      single glyph composed from components.  For instance, in Thai a
>      base consonant is composed with the following combining vowel as a
>      single glyph.  The value should be a character or a sequence
>      (vector, list, or string) of integers.
>
>         * If it is a character, it means to display that character
>           instead of the text in the region.
>
>         * If it is a string, it means to display that string's contents
>           instead of the text in the region.
>
>         * If it is a vector or list, the elements are characters
>           interleaved with internal codes specifying how to compose the
>           following character with the previous one.
>
> I must be misunderstanding this - perhaps someone can explain. I try this:
>
> (put-text-property
>   (point) (1+ (point))
>   'composition "Hi there!")
>
> I expected to see "Hi there!" displayed in place of the character before
> point ("display that strings contents instead of the text..."). Instead, I
> see no visible change. `C-u C-x =' shows that the composition property was
> applied. I also tried applying the property this way to several
> consecutive
> characters (expecting to see "Hi there!" in place of each), but with no
> visible change.
>
> I also tried looking at Emacs source code that uses this property, but I
> didn't find much, and what I found didn't enlighten me.
>
> What am I missing? Thx.
>
> BTW, should the text really be speaking of "the region" here? I tried with
> and without an active region, with no visible change. I suspect that this
> has nothing to do with the region, and I'd file a bug, but I don't yet
> understand this text (obviously). Shouldn't "the region" be "the
> characters
> with property `composition'"?
>
> Also, the illustration of Thai doesn't help (me) much. How about a code
> example, showing how `composition' can be used to compose a Thai consonant
> and its following vowel, forming a single glyph?