Triangles, rectangles, circles and other figures refer to geometric outlines, that is, peripheral shapes. Because the first condition for human beings to know and distinguish them is their appearance characteristics, that is, their shape characteristics. For example, the three corners of a triangle, the length of a rectangle and the length of a circle are all descriptions of its external contour and specific shape. Triangles, rectangles, and primitives are all two-dimensional planar graphics, and they all have surface components, which is the same. The difference is their outline shape.