[raster] Fix disappearing vertical lines (#54589).

* src/raster/ftraster.c (Vertical_Sweep_Span): Handle special case
where both left and right outline exactly pass pixel centers.

ChangeLog

@@ -1,3 +1,10 @@
+2018-09-21  Werner Lemberg  <wl@gnu.org>
+
+	[raster] Fix disappearing vertical lines (#54589).
+
+	* src/raster/ftraster.c (Vertical_Sweep_Span): Handle special case
+	where both left and right outline exactly pass pixel centers.
+
 2018-09-20  Alexei Podtelezhnikov  <apodtele@gmail.com>
 
 	* src/base/ftobjs.c (ft_glyphslot_reset_bimap): Tiny rounding tweak.

src/raster/ftraster.c

@@ -2246,13 +2246,18 @@
 
     /* Drop-out control */
 
-    e1 = TRUNC( CEILING( x1 ) );
+    e1 = CEILING( x1 );
+    e2 = FLOOR( x2 );
 
+    /* take care of the special case where both the left */
+    /* and right contour lie exactly on pixel centers    */
     if ( dropOutControl != 2                             &&
-         x2 - x1 - ras.precision <= ras.precision_jitter )
+         x2 - x1 - ras.precision <= ras.precision_jitter &&
+         e1 != x1 && e2 != x2                            )
       e2 = e1;
-    else
-      e2 = TRUNC( FLOOR( x2 ) );
+
+    e1 = TRUNC( e1 );
+    e2 = TRUNC( e2 );
 
     if ( e2 >= 0 && e1 < ras.bWidth )
     {