Abstract: In 2D graphic engine, visibility determination is very important. Through screen
clipping, it can reduce the quantity of polygon and ease the burden of the engine. So the screen
point inclusion test for planar polygon is important in screen clipping phase. In combination with
the 2D graphic engine characteristics, the popular algorithm is provided in DirectX platform
using c++ to implement test of inside- and outside-polygon points, and it is applied in 2D graphic
engine. The algorithm is proved to be simple and effective.

Key words: graphic processing, screen clipping, inside and outside point test, characteristic
polygon, polygon orientation