Bug with Recursive font

[khaledhosny]

HarfBuzz seems to have a problem applying variations to some glyphs of Recursive font downloaded from https://fonts.google.com/specimen/Recursive:

$ hb-shape Recursive-VariableFont_CASL,CRSV,MONO,slnt,wght.ttf -u c5 --variations="wght=300" --show-extents
[Aring=0+650<40,896,570,-896>]
$ hb-shape Recursive-VariableFont_CASL,CRSV,MONO,slnt,wght.ttf -u c5 --variations="wght=600" --show-extents
[Aring=0+650<0,0,0,0>]

hb-view also produces a blank image. FreeType font functions work fine:

$ hb-shape Recursive-VariableFont_CASL,CRSV,MONO,slnt,wght.ttf -u c5 --variations="wght=600" --font-funcs=ft --show-extents
[Aring=0+650<36,898,578,-898>]

Recursive.zip

[khaledhosny]

Interestingly, upstream files or even file downloaded directly from Google Fonts git repository do not show this problem:

$ hb-shape "Recursive[CASL,CRSV,MONO,slnt,wght].ttf" -u c5 --variations="wght=600" --show-extents
[Aring=0+650<36,898,578,-898>]

cc @rsheeter in case the download zip from the website is modified by some tool.

[behdad]

Reproduces for me.

[behdad]

There's a bug inside gvar's apply_deltas_to_points. glyf is bailing if that function returns false. That's wrong. But also if I make it not do that, the ring doesn't get variations applied whereas freetype does apply. Debugging further.

[behdad]

There's a bug inside gvar's apply_deltas_to_points

Looks to me like unpack_deltas is getting wrong bytes to unpack. This condition is being hit:

      if (j < run_count) 

[behdad]

I think we should apply this change regardless:

diff --git a/src/hb-ot-glyf-table.hh b/src/hb-ot-glyf-table.hh
index 066e152da..b4ac68834 100644
--- a/src/hb-ot-glyf-table.hh
+++ b/src/hb-ot-glyf-table.hh
@@ -820,8 +820,7 @@ struct glyf
       }
 
 #ifndef HB_NO_VAR
-      if (unlikely (!glyf_accelerator.gvar->apply_deltas_to_points (gid, font, points.as_array ())))
-       return false;
+      glyf_accelerator.gvar->apply_deltas_to_points (gid, font, points.as_array ());
 #endif
 
       switch (type) {