On Tue, Jul 17, 2018 at 4:18 AM, Richard Wordingham < [email protected]> wrote:
> On Mon, 16 Jul 2018 14:23:10 -0500 > Nathan Willis <[email protected]> wrote: > > > - If you are only casually using HarfBuzz but the shaping and layout > > issues have been a stumbling block in the past, what material would > > have helped > > This is a big hole, and perhaps off-topic Off-topic indeed. One problem lies in the change of advancewidth for glyphs > categorised as marks - there is a subtle difference between > Uniscribe/DirectWrite and HarfBuzz. It's also not at all clear to me > how position changes are supposed to interact with attachment. > I don't see a bug open about that. No bug, no fix. No bug, no clarification. :) > Another nightmare area is the rendering of <base, mark, base, mark> > when the bases ligate and the marks are required to interact. The root > of the problem is that Arabic requires that marks on components of > ligatures not interact, and that rule seems to apply even if the > ligature glyph is classified as a base rather than as a ligature. The first time I heard that this is a problem was a couple weeks ago from Zachary. I don't remember anyone filing a bug about this. Again, no bug, no fix. One area where I have just had to assume that 'here be dragons' is how > mark exclusions affect substitutions invoked by (chained) context > substitutions. Context substitutions seem to have odd limitations when > they invoke multiple ligations - perhaps I'm just seeing bugs in > Uniscribe. I know of one bug in HarfBuzz about that. But that's it. In my experience they work fine. Need specific examples. > There is also the undocumented restriction that subsidiary > substitutions be applied from start to end. I don't understand this. > Also, it seems that > invoked substitution have to have a matching context - invoking a > single substitution that has no effect, not even replacing a glyph by > itself, has seemed to cause trouble. > Need specifics. What trouble?
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