Attach CursivePositioning backwards, not forward

This is how Uniscribe does it.  So, adjust.  This is only relevant
to fonts that apply cursive positioning from a contextual lookup.

Fixes https://github.com/harfbuzz/harfbuzz/issues/1181

3 files changed, 11 insertions, 10 deletions

diff --git a/src/hb-ot-layout-gpos-table.hh b/src/hb-ot-layout-gpos-table.hh
index 746c2462..8b20c150 100644
--- a/src/hb-ot-layout-gpos-table.hh
+++ b/src/hb-ot-layout-gpos-table.hh
@@ -973,22 +973,22 @@ struct CursivePosFormat1
     hb_buffer_t *buffer = c->buffer;
 
     const EntryExitRecord &this_record = entryExitRecord[(this+coverage).get_coverage  (buffer->cur().codepoint)];
-    if (!this_record.exitAnchor) return_trace (false);
+    if (!this_record.entryAnchor) return_trace (false);
 
     hb_ot_apply_context_t::skipping_iterator_t &skippy_iter = c->iter_input;
     skippy_iter.reset (buffer->idx, 1);
-    if (!skippy_iter.next ()) return_trace (false);
+    if (!skippy_iter.prev ()) return_trace (false);
 
-    const EntryExitRecord &next_record = entryExitRecord[(this+coverage).get_coverage  (buffer->info[skippy_iter.idx].codepoint)];
-    if (!next_record.entryAnchor) return_trace (false);
+    const EntryExitRecord &prev_record = entryExitRecord[(this+coverage).get_coverage  (buffer->info[skippy_iter.idx].codepoint)];
+    if (!prev_record.exitAnchor) return_trace (false);
 
-    unsigned int i = buffer->idx;
-    unsigned int j = skippy_iter.idx;
+    unsigned int i = skippy_iter.idx;
+    unsigned int j = buffer->idx;
 
     buffer->unsafe_to_break (i, j);
     float entry_x, entry_y, exit_x, exit_y;
-    (this+this_record.exitAnchor).get_anchor (c, buffer->info[i].codepoint, &exit_x, &exit_y);
-    (this+next_record.entryAnchor).get_anchor (c, buffer->info[j].codepoint, &entry_x, &entry_y);
+    (this+prev_record.exitAnchor).get_anchor (c, buffer->info[i].codepoint, &exit_x, &exit_y);
+    (this+this_record.entryAnchor).get_anchor (c, buffer->info[j].codepoint, &entry_x, &entry_y);
 
     hb_glyph_position_t *pos = buffer->pos;
 
@@ -1035,7 +1035,7 @@ struct CursivePosFormat1
      * parent.
      *
      * Optimize things for the case of RightToLeft, as that's most common in
-     * Arabinc. */
+     * Arabic. */
     unsigned int child  = i;
     unsigned int parent = j;
     hb_position_t x_offset = entry_x - exit_x;
@@ -1064,7 +1064,7 @@ struct CursivePosFormat1
     else
       pos[child].x_offset = x_offset;
 
-    buffer->idx = j;
+    buffer->idx++;
     return_trace (true);
   }
 
diff --git a/test/shaping/data/in-house/fonts/9fc3e6960b3520e5304033ef5fd540285f72f14d.ttf b/test/shaping/data/in-house/fonts/9fc3e6960b3520e5304033ef5fd540285f72f14d.ttf
new file mode 100644
index 00000000..1841cf37
--- /dev/null
+++ b/test/shaping/data/in-house/fonts/9fc3e6960b3520e5304033ef5fd540285f72f14d.ttf
diff --git a/test/shaping/data/in-house/tests/cursive-positioning.tests b/test/shaping/data/in-house/tests/cursive-positioning.tests
index 74d283db..15a1ffc9 100644
--- a/test/shaping/data/in-house/tests/cursive-positioning.tests
+++ b/test/shaping/data/in-house/tests/cursive-positioning.tests
@@ -2,3 +2,4 @@
 ../fonts/298c9e1d955f10f6f72c6915c3c6ff9bf9695cec.ttf::U+0643,U+0645,U+0645,U+062B,U+0644:[gid8=4+738|gid5=3@441,1197+0|gid6=3@0,432+405|gid9=2@0,477+500|gid9=1@0,577+452|gid10=0@20,1177+207]
 #../fonts/706c5d7b625f207bc0d874c67237aad6f1e9cd6f.ttf::U+0B1F,U+0B4D,U+0B1A,U+0B4D,U+0B1A:[ttaorya=0+1307|casubscriptorya=0@-242,104+-231|casubscriptnarroworya=0@20,104+507]
 ../fonts/07f054357ff8638bac3711b422a1e31180bba863.ttf:--font-funcs=ot --no-glyph-names:U+0606,U+06E1:[2=0@40,502+0|1=0+1000]
+../fonts/9fc3e6960b3520e5304033ef5fd540285f72f14d.ttf::U+16F0A,U+16F57,U+16F8F:[u16F0A=0+422|u16F57=0@0,209+338|u16F8F=0+0]