Re: [stella] Grid demo

Subject: Re: [stella] Grid demo
From: John Saeger <john@xxxxxxxxxxx>
Date: Thu, 29 Oct 1998 12:47:42 -0800

Eckhard Stolberg wrote:
> At 15:03 28.10.98 -0800, you wrote:
> >> Look at trick18 or extra18.
> >> The last hits to RESP0/RESP1 both generate three copies.
> >
> >Hmmm.... I don't think so.  I don't think it's possible for a RESPx
> >other than the first one on a line to generate three copies.  Check out
> >the attached latehit.bin.  It has two groups of three sprites and I
> >don't think either of them overlap.  Yet only two sprites per group show
> >up.
> I made a small mistake, when I explained my theory in the last post,
> so I'll try again. When you set the sprites to two copies close, you
> will get an output like:
> ssssssssbbbbbbbbssssssssbbbbbbbbssssssssbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
> (s=sprite;b=background)
> My theory is: if you hit RESPx during the s part (atleast certain
> parts of it) you will get three copies. If you hit RESPx during the
> b part you will get only the last two copies.

O.K. I think you're right.  I was able to reproduce the three sprite
effect.  (See earlyb.bin)  earlyb does the first RESP0 at cycle 24,
giving nominal sprite positions of 9, 25 and 41 (start counting at
zero).  The second RESP0 is at cycle 35, giving nominal sprite positions
of 42, 58, and 74.  I see sprites at positions 25, 42, 58, and 74.  The
second sprite of the first group and the three sprites of the second
group.  But it's a pretty narrow target.  If the second RESP0 is one
cycle earlier(34), you only see three sprites total, one from the first
group and two from the second group.  If the second RESP0 is one cycle
later(36), you see two groups of two.  So I guess I believe in three
sprites now ;-)

Positioning seems perfectly normal.  The trick I think is to figure out
which RESPx a sprite belongs to.  Maybe not so easy to do.


Attachment: Earlyb.bin
Description: Binary data

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