Re: [stella] interlace / single line resolution

Subject: Re: [stella] interlace / single line resolution
From: kurt.woloch@xxxxxxxxx
Date: Fri, 23 Jun 2000 12:24:24 +0200
Glenn Saunders wrote:

>>Theoretically, on each scanline, you could have 5 objects (missiles,
>>players, ball), the playfield, and the 5 color registers, but it's
>>impossible to write to all of those registers in every scanline, so
>>constraints have to be made.
>Are you sure?  What about the intro of Super Football?  It's a six-char 
>with color register shifts on every scanline.  Not much going on with the 
>playfield, though, and no vertical movement, but I guess it could have any 
>regular playfield under it.

Well, this depends on what you mean with a "regular" playfield. From what I
get, you need nearly all cycles you have on a scanline for the six-char with
color register shifts. You can surely write a playfield pattern one or two
scanline before the six-char begins and leave it on (as it's done in Smurf's
Rescue with the energy bar), but you won't have time for playfield changes
on the scanlines where the six-chars are.

>>For instance, there are only few games displaying both players
>>on the same scanlines. Keystone Kapers does this, but I think the
>Radar Lock and Solaris color stripe just about everything all the time.
>Maybe we should look at the Solaris source for how that was done?  When you

>have 16K to work with, there are plenty of tricks you can pull.

Yes, especially if you use only plain black for space as background (or the
Solaris stars which don't require more CPU interaction).
You don't see many things going on with the playfield in Solaris, in fact.
When on the planets, both players are used and color-striped, but the
playfield doesn't need to be written, at least where the planet's
displayed... the black stripes can be done with the background color
register, and the holes in the planet are one of the players, since they
don't appear in one scanline with any enemy or one of their shots.
For Radar Lock, I've only seen a screenshot (doesn't start up with Z26 V.
1.01), but I suppose there aren't all PF registers written here at one
scanline. I suppose they do the horizon with a combination of the PF
registers and the ball, so when you bank, it's enough to write either PF0,
PF1 OR PF2 in one scanline, but not all three.
And judging from how the player's plane looks, it seems that it uses up both
players, so there won't be any enemies flying on these scanlines, and the
same color will be written to both player color registers there.

Judging from the games I have seen (with some exceptions like Jr. Pac-Man),
you can do up to about seven register re-writes per scanline. You have to
decide which ones are most important or make the most sense.

>>And this game also doesn't use color stripes at all (except for the
>>having different colors)
>Enduro DOES stripe the playfield, though, for the environmental effects,

Yes, but only on the scanlines ABOVE the road... where only the mountains
are shown. Since they are smooth scrolling, they can't be playfield... must
be some combination of players, missiles and ball.

They do color-stripe the road itself, but if you look closely, the changes
don't appear at the same scanline everytime, but move up and down, so I
suppose they just change the color when there's time left for it...

Glenn Saunders - Producer - Cyberpunks Entertainment
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