On 6/24/22 20:29, Behdad Esfahbod wrote:
Hi,
I've been looking at the internal Wine implementation of usp10.dll, and wondering if there is an interest to integrate with HarfBuzz instead / optionally.
Hi, Behdad.
Uniscribe implementation hasn't been touched in a while. DirectWrite implementation currently supports all types of GSUB/GPOS lookups, uses structure and code taken from harfbuzz wrt to feature masks, loop organization, sorting, etc. Currently it only implements Arabic shaping.
My longer term plan was to move all that to a separate textshaping.dll that modern Windows releases are using, and link to it from both gdi32 and dwrite, after removing existing uniscribe code. We don't need textshaping.dll interface to be compatible with Windows, because it's undocumented and isn't used by applications directly.
The main hindrance is that HarfBuzz does NOT currently provide separate substitution vs positioning steps ala ScriptShape() and ScriptPosition(). But I've been thinking about how to make that possibly happen, at least enough for Wine's needs.
Yes, I believe we talked about that some time (few years?) ago. Uniscribe's ScriptShape() and dwrite's GetGlyphs() are using very similar interface, and we'll need DWRITE_SHAPING_TEXT_PROPERTIES and DWRITE_SHAPING_GLYPH_PROPERTIES to be compatible with what Windows returns.
When I was working on this I found what some of the "reserved" fields mean in SHAPING_GLYPH_PROPERTIES, you can find structure definition in dlls/dwrite/dwrite_private.h:struct shaping_glyph_properties. I'm talking about last two fields "components" and "lig_component", that are important for GPOS handling.
Another field that harfbuzz does not provide I think is "DWRITE_SHAPING_GLYPH_PROPERTIES.justification" mask, which I believe is only useful for Arabic shaping, and roughly corresponds to character classes.
So technically, if we get correct ScriptShape()-style output from harfbuzz, including correct clustermap in WCHAR terms, we don't really need harfbuzz to produce ScriptPosition() output, because we have that implemented, and afaik it does not require script-specific handling, except maybe for features that have to be enabled.
Another consideration is that we'll likely have to import harfbuzz code, and build it as a static win32 library. That's not a decision I can make. I think the only build requirement would be a recent enough C++ compiler? And maybe ragel, at some point you had precompiled header in the tree. We'll have to ask Alexandre's opinion here.
We could also benefit from harfbuzz subsetter, and use it for fontsub and for Direct2D XPS printing.
Regards,
behdad http://behdad.org/