求一个几何图形的周长和面积，包括圆，三角形，四边形-For a perimeter and area of geometric shapes, including round, triangular, quadrilateral

java编写的点，线，四边形以及图形绘制，是彩色的哦！虽然简单，但是很适合初学者理解类的概念.-java write point, line, quadrilateral and graphics rendering, is the color of the Oh! Although simple, but very suitable for beginners to understand the concept of class.

描述了雪粒在网格中的运动，用到了四边形网格，双线性插值的概念-Described the snow particles movement in the grid, use the quadrilateral mesh, bilinear interpolation concept