AP_Camera: add singleton

libraries/AP_Camera/AP_Camera.cpp

@@ -444,3 +444,15 @@ void AP_Camera::update_trigger()
         }
     }
 }
+
+// singleton instance
+AP_Camera *AP_Camera::_singleton;
+
+namespace AP {
+
+AP_Camera *camera()
+{
+    return AP_Camera::get_singleton();
+}
+
+}

libraries/AP_Camera/AP_Camera.h

@@ -44,6 +44,10 @@ public:
     AP_Camera(const AP_Camera &other) = delete;
     AP_Camera &operator=(const AP_Camera&) = delete;
 
+    // get singleton instance
+    static AP_Camera *get_singleton() {
+        return _singleton;
+    }
 
     // MAVLink methods
     void            control_msg(const mavlink_message_t* msg);
@@ -71,6 +75,9 @@ public:
     void set_is_auto_mode(bool enable) { _is_in_auto_mode = enable; }
 
 private:
+
+    static AP_Camera *_singleton;
+
     AP_Int8         _trigger_type;      // 0:Servo,1:Relay
     AP_Int8         _trigger_duration;  // duration in 10ths of a second that the camera shutter is held open
     AP_Int8         _relay_on;          // relay value to trigger camera
@@ -127,3 +134,7 @@ private:
     bool using_feedback_pin(void) const { return _feedback_pin > 0; }
 
 };
+
+namespace AP {
+    AP_Camera *camera();
+};