compositor: surface and view output comment fixes

weston_surface::output and weston_view::output as used for different
purposes. Only the surface output is used for frame callbacks.

The uses of the view output are much more vague and hard to describe.

Also fix a comment mistake in weston_surface_assign_output().

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Yong Bakos <ybakos@humanoriented.com>
Reviewed-by: Armin Krezović <krezovic.armin@gmail.com>
[Pekka: more verbose on the compositor.h comments]

src/compositor.c

@@ -1082,16 +1082,15 @@ weston_surface_update_output_mask(struct weston_surface *es, uint32_t mask)
 	}
 }
 
-
 /** Recalculate which output(s) the surface has views displayed on
  *
  * \param es  The surface to remap to outputs
  *
  * Finds the output that is showing the largest amount of one
  * of the surface's various views.  This output becomes the
- * surface's primary output for vsync and frame event purposes.
+ * surface's primary output for vsync and frame callback purposes.
  *
- * Also notes the primary outputs of all of the surface's views
+ * Also notes all outputs of all of the surface's views
  * in the output_mask for the surface.
  */
 static void
@@ -1136,8 +1135,7 @@ weston_surface_assign_output(struct weston_surface *es)
  *
  * Identifies the set of outputs that the view is visible on,
  * noting them into the output_mask.  The output that the view
- * is most visible on is set as the view's primary output for
- * vsync and frame event purposes.
+ * is most visible on is set as the view's primary output.
  *
  * Also does the same for the view's surface.  See
  * weston_surface_assign_output().

src/compositor.h

@@ -949,8 +949,9 @@ struct weston_view {
 	} transform;
 
 	/*
-	 * Which output to vsync this surface to.
-	 * Used to determine, whether to send or queue frame events.
+	 * The primary output for this view.
+	 * Used for picking the output for driving internal animations on the
+	 * view, inheriting the primary output for related views in shells, etc.
 	 */
 	struct weston_output *output;
 
@@ -1019,7 +1020,9 @@ struct weston_surface {
 
 	/*
 	 * Which output to vsync this surface to.
-	 * Used to determine, whether to send or queue frame events.
+	 * Used to determine whether to send or queue frame events, and for
+	 * other client-visible syncing/throttling tied to the output
+	 * repaint cycle.
 	 */
 	struct weston_output *output;