Copy & Paste Pixels

Hi. How do I copy a line of pixels and paste it somewhere else? (eg. from [minX, maxX, Y] to somewhere) please help, thanks.

What is you are trying to achieve by this?

|------------------|
|******************| <-Copy from here
| | |
| | |
| | |
| | <–| to this position
|------------------|

Assuming that the square box above is my view port and those “*” are a line of pixels. Now I am trying to copy the whole line or maybe half of the line to the bottom of the screen. I am not familiar with glReadPixels, glCopyPixels and glDrawPixels. Please help me how to copy and paste pixels. Thanks.