by Michael S. Kaplan, published on 2005/10/18 03:31 -04:00, original URI: http://blogs.msdn.com/b/michkap/archive/2005/10/18/481654.aspx
Last January, I talked about Keeping it simple with complex scripts, and more recently I talked about Font Linking vs. Font Fallback.
One of the most important parts of that post was a quoting of the rules of what makes a script complex according to the rules of Uniscribe:
A complex script has at least one of the following attributes:
- Allows bidirectional rendering.
- Has contextual shaping.
- Has combining characters.
- Has specialized word-breaking and justification rules.
- The need to filter out some illegal character sequences.
The other day I was having a conversation with Peter Constable about a particular bug that we had found in Vista with particular languages that were showing those NULL GLYPHS (i.e. square boxes) rather than the characters in question. Since most font linking is really only used for CJK, it would be a font fallback problem.
Now as that second post explained, font fallback is what Uniscribe does. Did this bug indicate a bug in Uniscribe?
Peter explained to me that it was not really a bug, per se. Because the script in question was not one that was considered complex as per the above definitions. But clearly it did require special help to find the glyphs needed for display.
So clearly the script would need Uniscribe to have it on the list of scripts that would require font fallback. It has led to the consideration of needing yet another bullet point added to the definition of complex scripts so that the definition and the behavior could still remain consistent:
This would allow the behavior we see in Uniscribe in Vista to match the definition in the Vista update of the Platform SDK, particularly the update for the About Complex Scripts topic....
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