实现画图功能，主要包括矩形、画线等，能移动、放大、缩小等,The realization of drawing functions, including rectangular, painted lines, and can move, enlarge, narrow, etc.

模拟实现widows画板的部分功能。具有任意画线、线段、矩形、圆、橡皮功能。-Analog part of the realization of widows Sketchpad features. Arbitrary drawing lines, line segments, rectangular, round, rubber function.