mark (02/16/83)
The changes to make vi use scrolling regions on vt100's are indeed nice. And the original implementation did it using al and dl. But this suddenly meant you couldn't send termcaps freely around, because they weren't compatible. Also, it's much cleaner not to build stuff out of save cursor, change scrolling region, and restore cursor, and you can get much better performance when you want to insert/delete multiple lines if the capabilities are broken up. Vi won't use them unless sc/rc are also defined. cs leaves the cursor in an undefined location, thus it doesn't matter if it homes the cursor or not. (If someone has a terminal without sc/rc that leaves the cursor alone when you change the scrolling region, you're stuck.) The concept does not have scrolling regions. It has windows. Windows are different - cursor motion is relative to the window, not the whole screen, also, windows have 4 sides instead of 2. The changes to vi to support this are not short enough to post to the net. It makes more sense just to get a vi that supports vt100 scrolling regions from Berkeley. I'm sure such a vi is on 4.1a and later tapes.