Re: Unexpected font rendering with pango

[Jungshik Shin <jshin mailaps org>]

On 29 Jun 2003, Owen Taylor wrote:

> (The other thing that needs dealing with is dealing omitting
> non-rendering characters such as ZWJ from font selection to
> avoid having them break runs... fonts shouldn't have to claim to
> cover these languages)

  You meant 'claim to cover these characters', didn't you?
If that's what you meant,  it may not be so clear-cut for some
'invisible' characters.  For characters like 'invisible times'
(sorry I forgot the code point, it's somewhere in U+206x?  or can
be easily found in 'Default_Ignorable' list at Unicode ftp site)
and 'invisible  apply a function to'(?), there's no question that
they should be ignored. [1] It gets a bit murky for ZWJ and ZWNJ
(or CGJ).Some opentype fonts  have to claim to cover characters
like ZWJ and ZWNJ because ZWJ and ZWNJ take part in glyph substitutions
(via GSBU look-up) and their presence and absence affect the rendering
result.

[1] Some aggressive fonts have visible glyphs for truly invisible
characters. In presence of those fonts,  not taking 'truly invisible'
characters into account in font selection is essential to prevent
the visible glyph of 'invisible times' from one of those fonts from
popping up in the middle of a text-run rendered with another font.

Jungshik