Aztec

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Joined: Aug 12 2015
Posts: 148

This game has struck me as being an oddity.

I remember it being it in Hi-Res.
Which it is isn't?

UUpon close inspection I noticed that it has
purple borders.(Assuming you have a colour
monitor or TV. Sorry for those that do not)
This is not Hi-Res, but Lo-Res.

How do you get Hi-Res and Lo-Res on the
screen at once?

C056 - select Lo-Res
C057 - select Hi-Res
C054 - Hi-Res Page 1
C055 - Hi-Res Page 2
C053 - Mixed Mode - Hi-Res/Text Mode ONN
C052 - Mixed Mode OFF
C050 - TEXT mode off
C051 - TEXT mode ON

So where is the ability to display
Hi-Res and Lo-Res at the screen at once?

Did Datamost have some Apple II secrets
about the Apple II? (or Paul Stephenson)

I am quite curious.

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Offline
Joined: May 27 2009
Posts: 922
Re: Aztec

Hi-res with artifacting.
No lo-res.

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Joined: Sep 23 2016
Posts: 10
Re: Aztec

I thought I read something only a few weeks ago about rarely used graphics modes on the platform. I'm sure that I recall the term double lores being used (I presume 80-column lores), but also something even more unusual... lores as double hires. I think it was mentioned that the colours on "lores as double hires" are similar to, but not exactly the same as the colours on plain lores.

If my memory is correct, could your title of interest actually be "lores as double hires" with some sort of overlaid double hires border?

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Joined: Aug 12 2015
Posts: 148
Re: Aztec

Keatah

What is hi-res with artifacting?

Offline
Joined: May 27 2009
Posts: 922
Re: Aztec

The Apple II doesn't really generate colors in hi-res. It basically spikes the chroma signal at a specific time, and the monitor makes the color. So to speak. It doesn't send color information out the motherboard, just timed interference pulses.

Look at it this way, color comes about depending on the dot position, in the signal, and on the screen. Therefore the Apple doesn't store color information for the hi-res screen.

That's why if do do this
HGR : HCOLOR=3
HPLOT 50,50
HPLOT 55,55
..you'll see a purple and green dot.

But if you do this
HPLOT 60,60
HPLOT 61,60
..you'll see a larger white dot.

Or a white line like this..
HPLOT 50,70 TO 90,70

Or jailbars like so..
HPLOT 100,80 TO 100,100
HPLOT 103,80 TO 103,100

Now make one of them white..
HPLOT 99,80 TO 99,100

And the other..
HPLOT 104,80 TO 104,100

See? By timing the chroma spike to happen at different positions we get false color. Notice that we never changed the HCOLOR=3 statement. And yet we could change from green to purple to white by position alone.

You may want to refer to this material for a more thorough read.

https://en.wikipedia.org/wiki/Composite_artifact_colors#Apple_II

And Chapter 8 Page 6 of:
ftp://ftp.apple.asimov.com/pub/apple_II/documentation/hardware/machine/Understanding%20the%20Apple%20IIe.pdf

Beginning on Page 87 of this book is yet another explanation:
ftp://ftp.apple.asimov.com/pub/apple_II/documentation/programming/misc/APPLE_GRAPHICS_ARCADE_GAME_DESIGN.zip

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Offline
Joined: Aug 12 2015
Posts: 148
Re: Aztec

Yes I know about the pitfalls of Hi-Res pixel
display form the view point of assembly language.

But I did not know that you could do it from BASIC
without changing the HCOLOR.

Makes sense though.

Perhaps Apple's documents need to be updated/rectified?

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Joined: May 27 2009
Posts: 922
Re: Aztec

Not really, there are several mentions of the effect. Though they never use the word "artifacting". Artifacting (the term) came into use when unique graphics effects and alternate/textured colors could be "synthesized" with careful programming. Artifacting was accepted when those effects showed potential in games and later on paint programs.

Brian's Theme was the first popular program to show artifacting/mosaicking to the Apple II world in any significant numbers. Everybody ran this program back in the day!

---

I put in bold text the two manuals that have more in-depth technical explanations as opposed to mere mention of the effect.

Page 92 of The Applesoft Tutorial briefly introduces the issue of artifacting, just by saying even vs. odd horizontal positioning results in different colors.

Page 25, 26, 88, 89 of the Applesoft BASIC Programming Reference Manual make brief mention of the effect.

The section beginning on page 113 of the Apple IIe Applesoft Tutorial, once again, makes brief mention of the effect.

49163042-Apple-II-Applesoft-BASIC-Programmer-s-Reference-Manual-Volume-1 also notes the effect on page 146, and it tells you to reference the entry below..

Page 23-25 and 161-162 of the Apple IIe Reference Manual there is a good explanataion of what's going on with the phases of the hi-res colors. And why it happens.

Page 19 of the Apple II Reference Manual 1979 also explains the effect.

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