Add HB_DIRECTION_IS_FORWARD/BACKWARD

src/hb-common.h

diff --git a/src/hb-common.h b/src/hb-common.h
index d07b204..25249cc 100644
--- a/src/hb-common.h
+++ b/src/hb-common.h
@@ -81,6 +81,8 @@
 
 #define HB_DIRECTION_IS_HORIZONTAL(dir)	((dir) == HB_DIRECTION_LTR || (dir) == HB_DIRECTION_RTL)
 #define HB_DIRECTION_IS_VERTICAL(dir)	((dir) == HB_DIRECTION_TTB || (dir) == HB_DIRECTION_BTT)
+#define HB_DIRECTION_IS_FORWARD(dir)	((dir) == HB_DIRECTION_LTR || (dir) == HB_DIRECTION_TTB)
+#define HB_DIRECTION_IS_BACKWARD(dir)	((dir) == HB_DIRECTION_RTL || (dir) == HB_DIRECTION_BTT)
 
 
 #endif /* HB_COMMON_H */

src/hb-shape.c

diff --git a/src/hb-shape.c b/src/hb-shape.c
index 197d4a0..2605af6 100644
--- a/src/hb-shape.c
+++ b/src/hb-shape.c
@@ -130,8 +130,7 @@
 
   /* GPOS / kern */
 
-  /* TODO: Vertical */
-  if (buffer->direction == HB_DIRECTION_RTL)
+  if (HB_DIRECTION_IS_BACKWARD (buffer->direction))
     hb_buffer_reverse (buffer);
 
   buffer->direction = original_direction;