Question about screens - Sinclair

This is a discussion on Question about screens - Sinclair ; I was just musing the other day about what happened when you made other computers into Spectrums. My first experience of this was on the Memotech mtx range where a 64k machine loaded with the right Rom image etc, could ...

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Thread: Question about screens

  1. Question about screens

    I was just musing the other day about what happened when you made other
    computers into Spectrums. My first experience of this was on the Memotech
    mtx range where a 64k machine loaded with the right Rom image etc, could
    run many of the games.

    The problem was that circles were oval, so the Gyroscope, was oval, the
    wheels on buggies were oval etc, and the Scrabble board was stretched.

    When I was involved in the world of emulators, I was at pains to be sure
    that the writer did not fall into this trap. Even Sam had this problem to
    some extent.

    What is the situation these days, are games now all with round circles due
    to the standardisation of pc resolutions?

    Incidentally, getting back to the mtx, anyone know why now and again the
    vvidio would glitch sideways on part of a screen. I know this machine had a
    video processor chip so I assumed it was some kind of problem in the
    emulation of a Spectrum screen.

    Brian

    --
    Brian Gaff....Note, this account does not accept Bcc: email.
    graphics are great, but the blind can't hear them
    Email: briang1@blueyonder.co.uk
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  2. Re: Question about screens

    It may be that the MTX simply had different shaped pixels. Not all
    pixels are square. I don't know what the native display of the MTX was
    so I can't say if it was emulating the screen or not. The SAM had a
    compatible native mode, but again its pixels may have been a different
    shape. I believe modern emulators manage a pretty good approximation
    of the original cruddy 1980s television screens for the ultra
    nostalgic. I prefer my display crisp. FUSE has a widescreen mode that
    trims the upper and lower borders to maintain proper pixel shape in
    full screen mode on the newer 16:10 aspect ratio screens.

  3. Re: Question about screens

    I was told that the problem with differently shaped pixels is to do with
    the differing lines and frame rate in the states.

    I think the resolution of the mtx was the same as the Speccy, just kind of
    wide but not so tall.

    Yes, the Sam tended to be this way as well. I remember in Swansea when we
    were talking about it that he had a convincing answer, but I forgot it. He
    was more interested in midi and the w way the tape port coped with a speeded
    up tape deck as I recall, in between chain smoking Camel s and killing me...

    Brian

    --
    Brian Gaff - briang1@blueyonder.co.uk
    Note:- In order to reduce spam, any email without 'Brian Gaff'
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    Blind user, so no pictures please!
    "OwenBot" wrote in message
    news:9c031c0f-5b5c-49b1-a089-b8ca33edbccf@k7g2000hsd.googlegroups.com...
    > It may be that the MTX simply had different shaped pixels. Not all
    > pixels are square. I don't know what the native display of the MTX was
    > so I can't say if it was emulating the screen or not. The SAM had a
    > compatible native mode, but again its pixels may have been a different
    > shape. I believe modern emulators manage a pretty good approximation
    > of the original cruddy 1980s television screens for the ultra
    > nostalgic. I prefer my display crisp. FUSE has a widescreen mode that
    > trims the upper and lower borders to maintain proper pixel shape in
    > full screen mode on the newer 16:10 aspect ratio screens.




  4. Re: Question about screens

    On Tue, 19 Aug 2008 16:18:30 +0000, Brian Gaff wrote:
    > I was told that the problem with differently shaped pixels is to do with
    > the differing lines and frame rate in the states.


    Also cost reasons (RAM was expensive, plus some systems used a lot of
    extra hardware and/or a faster CPU to drive the display). Plus a specific
    display would usually be targetted, which had an impact - although
    typically for home machines this happened to be something which could
    also be substituted by a TV with little effort.

    There's been a few odd exceptions over the years - HP-250, or
    PERQ/Xerox/Apple machines with 'portrait' displays, for instance.



  5. Re: Question about screens

    Brian Gaff wrote:
    > The problem was that circles were oval, so the Gyroscope, was oval, the
    > wheels on buggies were oval etc, and the Scrabble board was stretched.


    It's all down to the pixel clock frequency. On the Sinclair machines,
    the pixel clock is twice the CPU clock, so a spectrum has a 7MHz pixel
    clock whereas a ZX81 has a 6.5MHz clock. Because of this, a ZX81 pixel
    takes slightly longer to draw and will be slightly wider than its
    spectrum equivalent (Despite having the same native resolution).

    I've just googled the MTX specifications and with its 4MHz CPU clock I'd
    guess it would have a native 8MHz pixel clock, making each pixel
    slightly narrower than the spectrum - that does mean it could fit more
    pixels across the screen though...

    Mike

  6. Re: Question about screens

    But that is not what we saw. It had wider than deep pixels which if the
    logic is right on your clock idea, ought have been the other way around!

    Brian

    --
    Brian Gaff - briang1@blueyonder.co.uk
    Note:- In order to reduce spam, any email without 'Brian Gaff'
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    Blind user, so no pictures please!
    "Mike Wynne" wrote in message
    newsPDqk.34967$ah4.31180@newsfe15.ams2...
    > Brian Gaff wrote:
    >> The problem was that circles were oval, so the Gyroscope, was oval, the
    >> wheels on buggies were oval etc, and the Scrabble board was stretched.

    >
    > It's all down to the pixel clock frequency. On the Sinclair machines, the
    > pixel clock is twice the CPU clock, so a spectrum has a 7MHz pixel clock
    > whereas a ZX81 has a 6.5MHz clock. Because of this, a ZX81 pixel takes
    > slightly longer to draw and will be slightly wider than its spectrum
    > equivalent (Despite having the same native resolution).
    >
    > I've just googled the MTX specifications and with its 4MHz CPU clock I'd
    > guess it would have a native 8MHz pixel clock, making each pixel slightly
    > narrower than the spectrum - that does mean it could fit more pixels
    > across the screen though...
    >
    > Mike




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