From: [email protected] [mailto:[email protected]] On Behalf Of Philippe Verdy
> But I suspect that the strong opposition given by Peter Constable... Yet again, I think you're putting words in my mouth. The only thing I think I've explicitly spoken against in this thread is changing the default bidi category of PUA characters to ON. > In fact when Peter says that the Bidi processing and the OpenType layout > engine are in separate layers (so that the OpenType layout works in a lower > layer and all BiDi processing is done before any font details are inspected), > I think that this is a perfect lie: The Unicode Bidi Algorithm uses _character_ properties and operates on _characters_. OpenType Layout tables deal only with glyphs. > At least the Uniscribe layout already has to inspect the content of any > OpenType > font, at least to process its "cmap" and implement the font fallback > mechanism, > just to see which font will match the characters in the input string to > render. > If it can do that, it can also inspect later a table in the selected font to > see which > PUAs are RTL or LTR. And it can do that as a source of information for BiDi > ... In theory, that could be done. A huge problem with your suggestion, though, is that the bidi algorithm deals only with characters and makes no references whatsoever to font data, and for that reason -- I would hazard to guess -- most implementations of the Unicode bidi algorithm do not rely in any way on font data and would need significant re-engineering to do so. Peter
