TODO: In this article, I’ll walk through how flutter rendering pipeline works by reading source code.

• Widget - Immutable blueprint of a part of interface.
  • Able to inflate an Element.
• Element - The use of a widget at a specific location of user interface.
  • Elements form a tree.
  • The widget associated with an element can change.
• RenderObject - Handle sizing, laying out, paiting and hit-testing.
  • RenderObjects form a tree as well.
  • Deal with rendering close to the metal.