[metrics] Scale up horizontal caret rise/run

Eg. if rise/run are 1/0, we now return upem/0. This is equivalent.

Part of https://github.com/harfbuzz/harfbuzz/pull/3338

src/hb-ot-metrics.cc

@@ -160,9 +160,20 @@ hb_ot_metrics_get_position (hb_font_t           *font,
     (position && (*position = font->em_scalef_y (face->table.TABLE->ATTR + GET_VAR)), true))
   case HB_OT_METRICS_TAG_HORIZONTAL_CLIPPING_ASCENT:  return GET_METRIC_Y (OS2, usWinAscent);
   case HB_OT_METRICS_TAG_HORIZONTAL_CLIPPING_DESCENT: return GET_METRIC_Y (OS2, usWinDescent);
-  case HB_OT_METRICS_TAG_HORIZONTAL_CARET_RISE:       return GET_METRIC_Y (hhea, caretSlopeRise);
-  case HB_OT_METRICS_TAG_HORIZONTAL_CARET_RUN:        return GET_METRIC_X (hhea, caretSlopeRun);
+
+  case HB_OT_METRICS_TAG_HORIZONTAL_CARET_RISE:
+  case HB_OT_METRICS_TAG_HORIZONTAL_CARET_RUN:
+  {
+    unsigned rise = face->table.hhea->caretSlopeRise;
+    unsigned upem = face->get_upem ();
+    unsigned mult = rise < upem ? upem / rise : 1;
+    if (metrics_tag == HB_OT_METRICS_TAG_HORIZONTAL_CARET_RISE)
+      return mult * GET_METRIC_Y (hhea, caretSlopeRise);
+    else
+      return mult * GET_METRIC_X (hhea, caretSlopeRun);
+  }
   case HB_OT_METRICS_TAG_HORIZONTAL_CARET_OFFSET:     return GET_METRIC_X (hhea, caretOffset);
+
 #ifndef HB_NO_VERTICAL
   case HB_OT_METRICS_TAG_VERTICAL_CARET_RISE:         return GET_METRIC_X (vhea, caretSlopeRise);
   case HB_OT_METRICS_TAG_VERTICAL_CARET_RUN:          return GET_METRIC_Y (vhea, caretSlopeRun);