RE: [stella] Higher Resolution through Interlacing

Subject: RE: [stella] Higher Resolution through Interlacing
From: "Billy Eno" <ceno@xxxxxxxxxxxxx>
Date: Wed, 14 Aug 2002 23:52:48 -0500
Chris,

This is from a month ago, I think I want to give it a shot.

You say you hit the RSYNC half way through line 262.  Then, you draw the
next interleaved frame, which is also 162 lines.  You said you have to play
with VSYNC, how do you play with it, does it just need to be hit at the same
time as the RSYNC, to get the display to start over at the top?

And, did you actually get this working on the 2600 at one point, or are you
talking about some other system?

Billy

> -----Original Message-----
> From: owner-stella@xxxxxxxxxxx [mailto:owner-stella@xxxxxxxxxxx]On
> Behalf Of Chris Wilkson
> Sent: Sunday, June 30, 2002 11:46 PM
> To: stella@xxxxxxxxxxx
> Subject: RE: [stella] Higher Resolution through Interlacing
>
>
> On Sun, 30 Jun 2002, Billy Eno wrote:
>
> > Interesting background on how TV's actually work.  I certainly
> was unaware.
> > It would be pretty easy to write a demo to see if it worked (I
> think), and I
> > may try.  But, if a TV interlaces two succesive Atari 2600 "frames" to
> > create an image, how would you (or the TV)know if the first frame was an
> > "odd" (to the TV) or an "even" (to the TV).  If the you didn't
> start with
> > the correct frame, likely the graphics wouldn't look right.
>
> The 2 fields should properly look like this:
>
> ********************              xxxxxxxxxx
> ********************    xxxxxxxxxxxxxxxxxxxx
> ********************    xxxxxxxxxxxxxxxxxxxx
> ********************    xxxxxxxxxxxxxxxxxxxx
> ********************    xxxxxxxxxxxxxxxxxxxx
> ********************    xxxxxxxxxxxxxxxxxxxx
> **********              xxxxxxxxxxxxxxxxxxxx
>      field 0                  field 1
>
> Notice that field 1 starts in midline, just where field 0 left off.  And
> field 0 starts at the beginning of the line, where field 1 left off.
> If you draw these 2 fields sequentially, you see how the lines get
> interlaced.  Remember that the lines are actually drawn diagonally,
> because the electron beam moves downward at a constant rate.  It's hard
> to draw in text, but I'll try.  Heres a display with 2.5 lines per field,
> or 5 lines per frame: (again, "*" represents field 0 and "x" represents
> field 1)
>
>
> *  x
>  *  x
>   *  x
> x  *
>  x  *
>   x  *
> *  x
>  *  x
>   *  x
> x  *
>  x  *
>   x  *
> *  x
>  *  x
>   *  x
>
> -Chris
>
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