[autofit] Improve BOUND action.

In complex glyph shapes, the original logic was too simple to cater
for situations that would actually need something similar to PS Hint
masks.  This fix should alleviate the worst cases.

* src/autofit/aflatin.c (af_latin_hint_edges): Don't allow
complete disappearance of stems.

ChangeLog

@@ -1,3 +1,14 @@
+2016-02-26  Werner Lemberg  <wl@gnu.org>
+
+	[autofit] Improve BOUND action.
+
+	In complex glyph shapes, the original logic was too simple to cater
+	for situations that would actually need something similar to PS Hint
+	masks.  This fix should alleviate the worst cases.
+
+	* src/autofit/aflatin.c (af_latin_hint_edges): Don't allow
+	complete disappearance of stems.
+
 2016-02-25  Werner Lemberg  <wl@gnu.org>
 
 	[autofit] Add blue-zone support for Tamil script.

src/autofit/aflatin.c

@@ -2885,14 +2885,21 @@
              ( top_to_bottom_hinting ? ( edge->pos > edge[-1].pos )
                                      : ( edge->pos < edge[-1].pos ) ) )
         {
+          /* don't move if stem would (almost) disappear otherwise; */
+          /* the ad-hoc value 16 corresponds to 1/4px               */
+          if ( edge->link && FT_ABS( edge->link->pos - edge[-1].pos ) > 16 )
+          {
 #ifdef FT_DEBUG_LEVEL_TRACE
-          FT_TRACE5(( "  BOUND: edge %d (pos=%.2f) moved to %.2f\n",
-                      edge - edges, edge->pos / 64.0, edge[-1].pos / 64.0 ));
+            FT_TRACE5(( "  BOUND: edge %d (pos=%.2f) moved to %.2f\n",
+                        edge - edges,
+                        edge->pos / 64.0,
+                        edge[-1].pos / 64.0 ));
 
-          num_actions++;
+            num_actions++;
 #endif
 
-          edge->pos = edge[-1].pos;
+            edge->pos = edge[-1].pos;
+          }
         }
       }
     }
@@ -3048,13 +3055,20 @@
              ( top_to_bottom_hinting ? ( edge->pos > edge[-1].pos )
                                      : ( edge->pos < edge[-1].pos ) ) )
         {
+          /* don't move if stem would (almost) disappear otherwise; */
+          /* the ad-hoc value 16 corresponds to 1/4px               */
+          if ( edge->link && FT_ABS( edge->link->pos - edge[-1].pos ) > 16 )
+          {
 #ifdef FT_DEBUG_LEVEL_TRACE
-          FT_TRACE5(( "  BOUND: edge %d (pos=%.2f) moved to %.2f\n",
-                      edge - edges, edge->pos / 64.0, edge[-1].pos / 64.0 ));
+            FT_TRACE5(( "  BOUND: edge %d (pos=%.2f) moved to %.2f\n",
+                        edge - edges,
+                        edge->pos / 64.0,
+                        edge[-1].pos / 64.0 ));
 
-          num_actions++;
+            num_actions++;
 #endif
-          edge->pos = edge[-1].pos;
+            edge->pos = edge[-1].pos;
+          }
         }
 
         if ( edge + 1 < edge_limit                                   &&
@@ -3062,14 +3076,21 @@
              ( top_to_bottom_hinting ? ( edge->pos < edge[1].pos )
                                      : ( edge->pos > edge[1].pos ) ) )
         {
+          /* don't move if stem would (almost) disappear otherwise; */
+          /* the ad-hoc value 16 corresponds to 1/4px               */
+          if ( edge->link && FT_ABS( edge->link->pos - edge[-1].pos ) > 16 )
+          {
 #ifdef FT_DEBUG_LEVEL_TRACE
-          FT_TRACE5(( "  BOUND: edge %d (pos=%.2f) moved to %.2f\n",
-                      edge - edges, edge->pos / 64.0, edge[1].pos / 64.0 ));
+            FT_TRACE5(( "  BOUND: edge %d (pos=%.2f) moved to %.2f\n",
+                        edge - edges,
+                        edge->pos / 64.0,
+                        edge[1].pos / 64.0 ));
 
-          num_actions++;
+            num_actions++;
 #endif
 
-          edge->pos = edge[1].pos;
+            edge->pos = edge[1].pos;
+          }
         }
       }
     }