Functionality like cursor movement

Hi,

I need to implement cursor like functionality on the LM3S9D96 microcontroller LCD screen.

I tried using doing it with scribble code and successful...but now the issues that need to be resovle are:

1. According to my understanding, when we draw cursor image on the screen the canvas pixels are changed. Now if i have text written say, 'Hello World' and place cursor over it, the pixels will be changed as per the cursor image, now when a move the cursor to some other location, how to regain the text pixels again, without reprinting the canvas.

2. secondly, what if the background is an image, not the single color like black used in scribble. how to reprint 20x20 area on the background without reprinting entire canvas.