2D game engine essentials [to be continued...]

All 2D Game Engines/Frameworks are trying to solve the same problem(s). Languages don't matter- they are simply the bricks that make things happen. (Flash/AS, HTML5/JS, Cocos/ObjectiveC, MFC, Swift, etc.)

Display:

Stage, Canvas, RootViewController, are essentially the same thing- the entry point of the view of an App.

DisplayContainer, Sprite, AnimatedSprite, MovieClip, they are just a family of displayable elements.

DisplayContainer has child nodes, which could have children too (hierarchical strucutre)

Animation, animations are basically a sequence of images being played at a certain speed/frame rate

Update/ticker funciton

Like in real world, things happen/progress as time elapses. In each timestep, coordinates being updated, images getting redrawed, calculation are performed, etc, etc.

Observer / Eventlisteners

They are just function pointers, upon events being fired, program looks into the registered function list. This method is opposed to polling, which constantly checking certain conditions in each update cycle.

Physics/AI:

In this way physics is independent from the game engine it's self, irrelevant to 2d or 3d, only the calculation space matters.