Success - Re: Skia-based ot-svg renderer hook to freetype

[Hin-Tak Leung]

See attached screenshot. Left is skia-based ftview/ftgrid, right is my 
system-wide ftview/ftgrid 2.13.0 (based on rsvg/cairo). The default zoom level 
for ftgrid seems to have changed between 2.13.0 and 2.13.1  from 4 to 6?

There are 3 issues I see

- the first one is of course the color - seems to be a rgba vs bgra difference? 
i.e. the Alpha channel is the same, but red and blue swapped.
- 2nd one is not very noticeable on ftview but more on ftgrid - the glyph is 
shifted down by one pixel. Probably a rounding error somewhere.
- I have intermitent crashes from 'include/core/SkRefCnt.h:72: fatal error: 
"assert(this->getRefCnt() > 0)" ' . Prove I don't know Skia well enough yet. ( 
That's one week of learning Skia ...)

On the way also learns a few things - this is based on m110 . I see that even 
with main (close to m116), one of the headers I am using have changed location.

I tried updating skia-python 's bundled skia from m87 to m88 - just 1 
milestone, or roughly 4 weeks, to get a feel of how easy/hard it is. The main 
reason is that m88 is the first where the SVGDOM class is declared 
non-experimental. So I expect the SVG related headers to move. But the actual 
diff is close to about 1000 lines, took me a whole day. (by comparison, the 
fontval diff is a little over 4000 lines, and took 3 years). The amount of 
changes in skia per milestone is just alarming. That explains why nobody wants 
to ship skia shared libraries, and why skia-python is stuck at m87 for 2 years. 
Skia is just contantly changing from milestone to milstone.

That said, I think somebody should update skia-python's bundled skia from m87 
to m98 (COLRv1) and perhaps even m103 (OT-SVG). Google folks?

One milestone is about 1000 lines of code difference and a whole day,  I reckon 
it will take somebody working full time for 2 months to update skia-python to 
current-ish. (116 - 87 = 29 working days..., by the time one gets to m116, 
m117/m118 would be out...). If google folks are not moving a finger, and 
somebody else wants to fund me to tackle this, please feel free to get in touch.


I'll tidy the diff up and send it to freetype-devel at some point. At the 
moment it is just replacing all contents of rsvg-port.{c,h}. with 

-#ifdef HAVE_LIBRSVG
+#ifdef HAVE_SKIA
...
 
-  SVG_RendererHooks  rsvg_hooks = { NULL, NULL, NULL, NULL };
+  SVG_RendererHooks  skia_hooks = { NULL, NULL, NULL, NULL };
...
     (void)FT_Property_Set( handle->library,
-                           "ot-svg", "svg-hooks", &rsvg_hooks );
+                           "ot-svg", "svg-hooks", &skia_hooks );
...

So potentionally I can add a toggle key to dynamically switch between 
rsvg/cairo to skia rendering by just swapping  &rsvg_hooks with &skia_hooks on 
the fly.

skia-based Screenshot from 2023-07-12 06-02-51.png
Description: PNG image