Drawing statically in Open GL

I am developing a paint-like application using C++ and Open GL. But every time i draw objects like circle, lines etc they don't ** stay ** on th开发者_StackOverflowe page. By this I mean that every new object I draw is getting placed on a blank page. How do I get my drawn objects to persist?

OpenGL has no geometry persistency. Basically it's pencils, brushes and paint, with which you draw on a canvas called the "framebuffer". So after you drawn something and clear the framebuffer, it will not reappear in some magic way.

There are two solutions:

• you keep a list of all drawing operations and at each redraw you repaint everything from that list.

• After drawing something copy the image in the framebuffer to a texture and instead of glClear you fill the background with that texture.

Both techniques can be combined.

Just don't clear the framebuffer and anything you draw will stay on the screen. This is the same method I use to allow users to draw on my OpenGL models. This is only good for marking up an image, since by using this method you can't erase what you've drawn, unless your method of erasing is to draw using your background color.