cursor-renderer: Track cursor position using floats

To be able to render the pointer cursor sprite at sub-(logical)-pixel
positions, track the pointer position using floats instead of ints.
This also requires users of the cursor sprite rect to deal with
floating points, when e.g. finding the logical monitor etc.

https://bugzilla.gnome.org/show_bug.cgi?id=765011

src/core/boxes-private.h

@@ -218,4 +218,19 @@ GList* meta_rectangle_find_nonintersected_monitor_edges (
 gboolean meta_rectangle_is_adjecent_to (MetaRectangle *rect,
                                         MetaRectangle *other);
 
+static inline ClutterRect
+meta_rectangle_to_clutter_rect (MetaRectangle *rect)
+{
+  return (ClutterRect) {
+    .origin = {
+      .x = rect->x,
+      .y = rect->y
+    },
+    .size = {
+      .width = rect->width,
+      .height = rect->height
+    }
+  };
+}
+
 #endif /* META_BOXES_PRIVATE_H */

src/core/screen.c

@@ -1286,21 +1286,25 @@ find_highest_logical_monitor_scale (MetaBackend      *backend,
     meta_backend_get_monitor_manager (backend);
   MetaCursorRenderer *cursor_renderer =
     meta_backend_get_cursor_renderer (backend);
-  MetaRectangle cursor_rect;
+  ClutterRect cursor_rect;
   GList *logical_monitors;
   GList *l;
   int highest_scale = 0.0;
 
   cursor_rect = meta_cursor_renderer_calculate_rect (cursor_renderer,
-                                                     cursor_sprite);
+						     cursor_sprite);
 
   logical_monitors =
     meta_monitor_manager_get_logical_monitors (monitor_manager);
   for (l = logical_monitors; l; l = l->next)
     {
       MetaLogicalMonitor *logical_monitor = l->data;
+      ClutterRect logical_monitor_rect =
+	      meta_rectangle_to_clutter_rect (&logical_monitor->rect);
 
-      if (!meta_rectangle_overlap (&cursor_rect, &logical_monitor->rect))
+      if (!clutter_rect_intersection (&cursor_rect,
+				      &logical_monitor_rect,
+				      NULL))
         continue;
 
       highest_scale = MAX (highest_scale, logical_monitor->scale);