Easy, 2D is harder because it can have hard edges. Look at any 3D game, the edges of the polygons are obscured by antialiasing methods and texture wrapping. In

Easy, 2D is harder because it can have hard edges. Look at any 3D game, the edges of the polygons are obscured by antialiasing methods and texture wrapping. In 2D, you need to draw a line at some arbitrary angle (or worse, a spline!) where on one side there's black and on the other side white. You will have to fake this with subpixel rendering. You also need to detect when the subpixels would interfere with the actual line width. You need to be able to snap two objects together that fit together seamlessly in the mathematical sense, without a sliver in-between popping in and out of existence. Anyone who has tried to fake 2D using 3D rendering (such as inside a game engine) has likely run into the above issues.