libcamera: controls: Add support for querying direction information

Add support to ControlId for querying direction information. This allows
applications to query whether a ControlId is meant for being set in
controls or to be returned in metadata or both. This also has a side
effect of properly encoding this information, as previously it was only
mentioned losely and inconsistently in the control id definition.

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/libcamera/control_serializer.cpp

@@ -281,6 +281,7 @@ int ControlSerializer::serialize(const ControlInfoMap &infoMap,
 		entry.id = id->id();
 		entry.type = id->type();
 		entry.offset = values.offset();
+		entry.direction = static_cast<ControlId::DirectionFlags::Type>(id->direction());
 		entries.write(&entry);
 
 		store(info, values);
@@ -493,12 +494,17 @@ ControlInfoMap ControlSerializer::deserialize<ControlInfoMap>(ByteStreamBuffer &
 
 		/* If we're using a local id map, populate it. */
 		if (localIdMap) {
+			ControlId::DirectionFlags flags{
+				static_cast<ControlId::Direction>(entry->direction)
+			};
+
 			/**
 			 * \todo Find a way to preserve the control name for
 			 * debugging purpose.
 			 */
 			controlIds_.emplace_back(std::make_unique<ControlId>(entry->id,
-									     "", "local", type));
+									     "", "local", type,
+									     flags));
 			(*localIdMap)[entry->id] = controlIds_.back().get();
 		}