OpenGL graphics editor...implementation of eraser tool

i'm writing a menu-based OpenGL graphics ed开发者_JS百科itor.It is pretty basic. Every time i choose a new option in the pop-down menu, the older drawing disappears,this doesn't allow me to use the eraser tool...could anybody tell me how to solve this problem?thanx

Your question is vague. Anyway...

Are you drawing picture directly on the screen/window? Then of COURSE drawings will disappear.

Paint picture to texture (framebufferObjects or whatever. See NVidia OpenGL SDK for examples). Then render texture on the screen. clear screen, draw texture, then draw menu, every time you need to repaint window.