Re:A Great Old-Timey Game-Programming Hack
by chipsy on Monday December 16, 2013 @08:20PM
(#6919065)
My own understanding was that it was just that particular configuration of the EGA hardware that hadn't been tried before Carmack's implementation.
This is someone who found out from Romero exactly what the Keen games did: http://www.vintage-computer.com/vcforum/showthread.php?30619...
You discuss Carmack's pixel scrolling and miss the fact that this guy here who claims he did "the same" just had to draw one character of the snake's head at the new position, overwriting the previous head with the "body" character. And the tail character with the "empty" character unless the snake eats something.
What in the world has that to do with Carmack's algorithm of updating Mario after one pixel hardware scroll (after which he has to redraw the "unmoving" part fully) and adding more background once he spends the hardware moves?
Same principle, as I see it, whether it's writing 1 byte, calling gotoxy/putch, or copying a whole bunch of bytes. Dirty rects! The insight is the same: you draw the things that have changed, and leave alone the things that stay the same.
The cunning part of the Carmack games was presumably widening the screen - I don't think I ever saw this done on the BBC. But as a schoolboy in 1989/1990 I'd experimented with reducing the BBC's screen height by one character row (by tweaking R6) to avoid flicker when scrolling vertically. Same principle. It's a fairly obvious thing to do, once you've figured out what's going on.
I think one can come up with better evidence for John Carmack's uniquely amazing skills.