[subset] Correct usFirstCharIndex and usLastCharIndex in OS2 table when subsetting.

src/hb-ot-os2-table.hh

@@ -49,6 +49,51 @@ struct os2
     return_trace (c->check_struct (this));
   }
 
+  inline hb_blob_t * subset (hb_subset_plan_t *plan, hb_face_t *source) const
+  {
+    hb_blob_t *os2_blob = OT::Sanitizer<OT::os2>().sanitize (hb_face_reference_table (source, HB_OT_TAG_os2));
+    hb_blob_t *os2_prime_blob = hb_blob_create_sub_blob (os2_blob, 0, -1);
+    hb_blob_destroy (os2_blob);
+
+    OT::os2 *os2_prime = (OT::os2 *) hb_blob_get_data_writable (os2_prime_blob, nullptr);
+    if (unlikely (!os2_prime)) {
+      hb_blob_destroy (os2_prime_blob);
+      return nullptr;
+    }
+
+    uint16_t min_cp, max_cp;
+    find_min_and_max_codepoint (plan, &min_cp, &max_cp);
+    os2_prime->usFirstCharIndex.set (min_cp);
+    os2_prime->usLastCharIndex.set (max_cp);
+
+    return os2_prime_blob;
+  }
+
+  static inline void find_min_and_max_codepoint (hb_subset_plan_t *plan,
+                                                 uint16_t         *min_cp, /* OUT */
+                                                 uint16_t         *max_cp  /* OUT */)
+  {
+    hb_codepoint_t min = -1, max = 0;
+
+    for (int i = 0; i < plan->codepoints.len; i++) {
+      hb_codepoint_t cp = plan->codepoints[i];
+      if (cp < min) {
+        min = cp;
+      }
+      if (cp > max) {
+        max = cp;
+      }
+    }
+
+    if (min > 0xFFFF)
+      min = 0xFFFF;
+    if (max > 0xFFFF)
+      max = 0xFFFF;
+
+    *min_cp = min;
+    *max_cp = max;
+  }
+
   public:
   HBUINT16	version;
 

src/hb-subset.cc

@@ -38,6 +38,7 @@
 #include "hb-ot-glyf-table.hh"
 #include "hb-ot-head-table.hh"
 #include "hb-ot-maxp-table.hh"
+#include "hb-ot-os2-table.hh"
 
 
 #ifndef HB_NO_VISIBILITY
@@ -349,6 +350,9 @@ _subset_table (hb_subset_plan_t *plan,
     case HB_OT_TAG_cmap:
       dest_blob = _subset<const OT::cmap> (plan, source);
       break;
+    case HB_OT_TAG_os2:
+      dest_blob = _subset<const OT::os2> (plan, source);
+      break;
     default:
       dest_blob = source_blob;
       break;
@@ -360,17 +364,17 @@ _subset_table (hb_subset_plan_t *plan,
 }
 
 static bool
-_should_drop_table(hb_tag_t tag) 
+_should_drop_table(hb_tag_t tag)
 {
     switch (tag) {
-      case HB_TAG('G', 'D', 'E', 'F'): /* temporary */
-      case HB_TAG('G', 'P', 'O', 'S'): /* temporary */
-      case HB_TAG('G', 'S', 'U', 'B'): /* temporary */
-      case HB_TAG('d', 's', 'i', 'g'):
+      case HB_TAG ('G', 'D', 'E', 'F'): /* temporary */
+      case HB_TAG ('G', 'P', 'O', 'S'): /* temporary */
+      case HB_TAG ('G', 'S', 'U', 'B'): /* temporary */
+      case HB_TAG ('d', 's', 'i', 'g'):
         return true;
       default:
         return false;
-  } 
+  }
 }
 
 /**