thx rob reply me ,but i want to ask what is framebuffer first,
does it any difference with reading a bmp into memory??
i have found some code which can change bmp into memory,but i don't know how can change the bmp in memory to framebuffer?
The framebuffer is the memory where OpenGL will put all the pixels, today this memory is almost always in memory on the videocard so you will not be able to use it as you do with normal RAM.
You use glReadPixels and glDrawPixels to read and write data from/to the framebuffer.
If you need to do fast updates you might want to use a texture instead of glDrawPixels.