First step in refactoring: brought both Paint and Mapping under the common umbrella class Element and implemented basic QProperties.

Mapping.cpp

@@ -23,25 +23,15 @@
 UidAllocator Mapping::allocator;
 
 Mapping::Mapping(Paint::ptr paint, MShape::ptr shape, uid id)
-  : _paint(paint), _shape(shape),
-    _isLocked(false), _isSolo(false), _isVisible(true), _opacity(1.0f)
+  : Element(id, &allocator),
+    _paint(paint), _shape(shape),
+    _isSolo(false), _isVisible(true)
 {
-  if (id == NULL_UID)
-    id = allocator.allocate();
-  else
-  {
-    Q_ASSERT(!allocator.exists(id));
-    allocator.reserve(id);
-  }
-
-  // Assign id.
-  _id = id;
-
   // Default.
-  _depth = _id;
+  _depth = getId();
 }
 
 Mapping::~Mapping() {
-  allocator.free(_id);
+  allocator.free(getId());
 }