c# - When I minimize my application all of my drawings disappears -

i building c# app shows trajectory of cannonball. when minimize trajectory have drawn picture box gone when bring up. there easy way stop this?

i bet drawing in mouse event. use onpaint event , should go.

edit:

here decent drawing tutorial using onpaint() event:

http://www.geekpedia.com/tutorial50_drawing-with-csharp.html