boxes: Add 'round' rounding strategy

It just calls roundf(), and is intended to be used when the graphene
rectangle is approximately integer aligned.

https://gitlab.gnome.org/GNOME/mutter/merge_requests/1042

src/core/boxes-private.h

@@ -45,6 +45,7 @@ typedef enum _MetaRoundingStrategy
 {
   META_ROUNDING_STRATEGY_SHRINK,
   META_ROUNDING_STRATEGY_GROW,
+  META_ROUNDING_STRATEGY_ROUND,
 } MetaRoundingStrategy;
 
 /* Output functions -- note that the output buffer had better be big enough:

src/core/boxes.c

@@ -2151,6 +2151,15 @@ meta_rectangle_from_graphene_rect (const graphene_rect_t *rect,
         };
       }
       break;
+    case META_ROUNDING_STRATEGY_ROUND:
+      {
+        *dest = (MetaRectangle) {
+          .x = roundf (rect->origin.x),
+          .y = roundf (rect->origin.y),
+          .width = roundf (rect->size.width),
+          .height = roundf (rect->size.height),
+        };
+      }
     }
 }