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TI-99/4A vs ZX81

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Correction, the color board for the Atom was extra... but at least it was an option.

 

Coming from a proud 'Acorn Atom family', I don't recall there being a power switch either. Just had the power lead from the transformer plugging into the jack on the back panel.

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A lot of computers (and some consoles) seem to have lacked power switches, like those were not really required and would involve a lot of extra circuitry to install one. The UK computers in particular seem to have been switchless to a large degree: ZX-80/81, ZX Spectrum, Oric-1 & Atmos, Acorn Atom... if it wasn't for being a school computer, I'm sure the Beeb would've lacked a proper power switch as well.

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The isometric games are optimized to update only the changed area of video. So it hides the relative slowness of MSX versus Spectrum.

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In the line 40s you've got X=SQR(A). It should be A=SQR(A). That might be the cause of the error you're seeing.

Hmm thanks, but that has no effect on the error or the time it takes.

 

Corrected line 40 results

RXB: 3 minutes 40 seconds with .00000011 and .009752232

Edited by RXB

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Corrected

 

RXB: 3 minutes 40 seconds with .00000011 and .009752232

 

XB : 5 minutes 45 seconds with .00000011 and 6.27999115

 

Basic: 4 minutes 24 seconds with .00000011 and 1.928494715

Edited by RXB
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Coming from a proud 'Acorn Atom family', I don't recall there being a power switch either. Just had the power lead from the transformer plugging into the jack on the back panel.

Really? Hmmm... I could have sworn I saw a photo of one with a switch on the power supply.

I guess it might not have been the factory power unit, or a mod.

Then again I've seen so many classic computers it could have been a power supply for a different machine.

 

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The isometric games are optimized to update only the changed area of video. So it hides the relative slowness of MSX versus Spectrum.

 

Do you know any details about the algorithms they used?

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Do you know any details about the algorithms they used?

No. Never had the courage to dive into disassembling it :grin:

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Do you know any details about the algorithms they used?

The source for Space 1999 on the Oric is available, and at one time there was a detailed pdf on creating the isometric engine.

*edit*

FWIW, the memory layout use by the 9918 should work out pretty well for this.

3 moving objects would probably require updating less than 100 bytes even in the worst case.

 

Source:

http://miniserve.defence-force.org/svn/public/oric/games/Space%201999/

 

 

Edited by JamesD

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The source for Space 1999 on the Oric is available, and at one time there was a detailed pdf on creating the isometric engine.

*edit*

FWIW, the memory layout use by the 9918 should work out pretty well for this.

3 moving objects would probably require updating less than 100 bytes even in the worst case.

 

Source:

http://miniserve.defence-force.org/svn/public/oric/games/Space%201999/

 

 

 

 

If it's objects like these from Knight Lore each of them takes more than 100 bytes. ;-)

 

post-35226-0-62024000-1496501129.gifpost-35226-0-65302200-1496501137.gifpost-35226-0-00747900-1496501144.gif

 

But I guess you're right that the VDP transfer is not the limiting factor for isometric games with few moving obejcts .

 

I'm still struggling to understand how the drawing in the off-screen buffer works, i.e. how to determine which of the isometric blocks and sprites you have to redraw when an object moves.

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Why not plot all of them from the one with the biggest distance from the screen?

Otherwise you need to test 2d collisions among all the objects in the room

Edited by artrag

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Why not plot all of them from the one with the biggest distance from the screen?

Otherwise you need to test 2d collisions among all the objects in the room

 

So in this case (image), if the man if moved you would redraw everything within the orange box?

 

post-35226-0-00872700-1496523372.png

 

I think that might be too expensive, but it does make a very simple algorithm.

 

Edit: and some of the blocks behind the man would also have to be redrawn.

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On 5/29/2017 at 9:41 PM, LASooner said:

Anyone who ever, keyed in a program into the ZX81 membrane keyboard for several hours only to knock the 2k ram pack by mistake before it could be saved to tape, would never ask this question.

 

TPi8gE6.jpg

😆

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Having had a ZX Spectrum back then, I have to admit that the TI was a very good home computer, with its full typewriter keyboard, sound chip and even 16 bit processor in 1981.

Its problems were not of technical, but of business/marketing nature.

When Jack Tramiel released the C64 in 1982, he saw the TI as its main competitor and started a price war against the TI.

A big argument against the TI was, that Texas Instruments licensed only certain developers to program their proprietary processor and the cartridges (which the developers even had to buy).

While the C64 was open to everybody who wanted to program it, so that a large software library was built up over time. Texas Instruments made a big mistake there.

In the end that ruined the TI (that was, as mentioned, in itself pretty good), and it was given away cheap. So that customers even wondered, why it was so cheap - was there something wrong with it, maybe?

 

 

So there you have it: A technically good machine, that nevertheless couldn't compete on the market for other reasons.

While the Sinclair machines, although technically maybe not quite as good, were a commercial success, especially the Spectrum. Its system (even with the rubber keyboard, the beeper and the cassette tape as storage device) did make sense and I had a lot of fun with it.

The ZX81, well, in my opinion it was too reduced, too limited to be really useful. Similar to the VIC-20 with just 3,5K RAM. But some people even liked these. Well, it were just the predecessors to the machines to come, the Spectrum and the C64.

Edited by Pokeypy
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I used to drool over the ads for the ZX-81 in magazines as it was the only computer that seemed to be almost within my financial reach. Ended up (luckily) with a TI console instead (thanks mom and dad!). I do have a complete ZX-81 system now including a ZXpander with SD storage but sadly it has seen very little use lately with only 2 Basic programs to my name (WLANDER and WRACE which I believe are out there). I even keep a portable 5" B&W TV/radio combo just for it. The ZXpander really opens up a lot of possibilities, including a Forth version! 

 

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