## 3.7画封闭的线，一次连接个顶点 ``` void fl_polygon(int x, int y, int x1, int y1, int x2, int y2) void fl_polygon(int x, int y, int x1, int y1, int x2, int y2, int x3, int y3) ``` Fill a 3 or 4-sided polygon. The polygon must be convex.