Thread: Displaying more shapes in the same client Area

Dear Friends
I am a Teacher. At present I face a problem in drawing different shapes in the client area of my window . I am using SDK(WIN32 API).
My problem: Drawing shapes in the client area
1. I select a shape from the menu(resource)
2. I start by dragging the mouse in the client area(the shape keep growing), when I release the mouse the shape will be there.
3. Now I select another shape and drag, the new shape will keep drawing on the client area, but on invalidation the previous shape disappers.
How can I retain the previous shape on invalidating only a particular part.
(I call InvalidateRect() in each WM_MOUSEMOVE with MK_LBUTTON down).
Please provide me a solution soon.
Have a nice day
Bye