[subset] Add some comments to find_space_roots/find_32_bit_roots methods.
diff --git a/src/graph/graph.hh b/src/graph/graph.hh
index 88a9e4e..49638f3 100644
--- a/src/graph/graph.hh
+++ b/src/graph/graph.hh
@@ -264,6 +264,11 @@
hb_swap (vertices_, sorted_graph);
}
+ /*
+ * Finds the set of nodes (placed into roots) that should be assigned unique spaces.
+ * More specifically this looks for the top most 24 bit or 32 bit links in the graph.
+ * Some special casing is done that is specific to the layout of GSUB/GPOS tables.
+ */
void find_space_roots (hb_set_t& visited, hb_set_t& roots)
{
int root_index = (int) root_idx ();
@@ -285,7 +290,9 @@
if (l.width == 3)
{
// A 24bit offset forms a root, unless there is 32bit offsets somewhere
- // in it's subgraph, then those become the roots instead.
+ // in it's subgraph, then those become the roots instead. This is to make sure
+ // that extension subtables beneath a 24bit lookup become the spaces instead
+ // of the offset to the lookup.
hb_set_t sub_roots;
find_32bit_roots (l.objidx, sub_roots);
if (sub_roots) {
@@ -451,6 +458,10 @@
find_subgraph (link.objidx, subgraph);
}
+ /*
+ * Finds the topmost children of 32bit offsets in the subgraph starting
+ * at node_idx. Found indices are placed into 'found'.
+ */
void find_32bit_roots (unsigned node_idx, hb_set_t& found)
{
for (const auto& link : vertices_[node_idx].obj.all_links ())
