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Why Does The Border Have to Be White?

Posted: Mon Apr 01, 2024 1:45 pm
by Fruitcake
Doesn't time fly? It's the beginning of April already! What better than to start off the first day of the new month with an interesting development.

Have you ever played a ZX81 game that is set on a black background but felt that the look of it was somewhat let down by the border having to remain white? For instance, here is Macronics' Space Intruders:

SpaceIntrudersWhiteBorder.png
SpaceIntrudersWhiteBorder.png (3.82 KiB) Viewed 1496 times

Wouldn't a Space Invaders clone like this look much nicer with the border black? Imagine if it could look like this:

SpaceIntrudersBlackBorder.png
SpaceIntrudersBlackBorder.png (3.67 KiB) Viewed 1496 times

If you think about it, when you run something in FAST mode then the whole screen goes black, which proves that the hardware is capable of displaying black in the border area. So why can't the border be black and the game displayed in the centre of the screen as normal? Well, it actually turns out that this can be done!! I know, who knew?!!

Now I appreciate this might sound quite unbelievable but you can try it out for yourself, either in an emulator or ideally on a real ZX81 (assuming you can get a good stable picture from it normally). No special hardware is required; just a standard ZX81 with 16K RAM. Here is the enhanced black border version of Space Intruders for you to try out:

SpaceIntruders(BlackBorder).p
(1.7 KiB) Downloaded 88 times

I feel a little foolish now for having thought all these years that this just wasn't possible on the ZX81!

Re: Why Does The Border Have to Be White?

Posted: Mon Apr 01, 2024 2:37 pm
by Moggy
Thankfully anyone with a ZX8-CCB (nearly all of us ) have that facility built in, hmmm what's todays date? :lol:

Re: Why Does The Border Have to Be White?

Posted: Wed Apr 03, 2024 12:47 am
by Fruitcake
Well, today is the 2nd of April. And for those of us that don't have a ZX8-CCB fitted then a software mechanism that can output the border black will just have to do.

Re: Why Does The Border Have to Be White?

Posted: Fri Apr 05, 2024 11:32 pm
by stroebeljc
Here is a 60Hz version for those, like me, afflicted with NTSC, including source code (compiled using TASM with NTSC defined). I'm stuck with a white line at the top because of how little processing time is left over for gameplay. Any ideas on how to remove it, if possible?
60Hz.png
60Hz.png (3.81 KiB) Viewed 1179 times

Re: Why Does The Border Have to Be White?

Posted: Tue Apr 09, 2024 5:57 pm
by stroebeljc
I did a bit more work on this, but still have some white bars at the top and bottom on the 60Hz build. The problem is that eliminating the white bars slows gameplay too much. So, here is where I've ended up.
50Hz
New 50Hz.png
New 50Hz.png (3.84 KiB) Viewed 1054 times
60Hz
New 60Hz.png
New 60Hz.png (3.33 KiB) Viewed 1054 times