Introduction - If you have any usage issues, please Google them yourself
a) GDI Basic Drawing: rectangle, line, ellipse, rounded rectangle, pencil drawing, multi-line (not closed), polygons (closed), a half-hyun. b) borders and color settings. c) for each layer to support the process of painting. d) Each layer supports drag process. e) in the OnDraw function, use double buffering technology to prevent flicker