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Thread: M4 pixels not all the same size. really?

  1. #1

    Default M4 pixels not all the same size. really?

    Ok, so I've been trying to debug *why* the m4 graphics characters aren't correct.

    Then i find this;




    SO the M4 _really_ does have different sized pixels every 3rd line - or am i going mad!

    If this is true, is there any way to fix this?

    thanks.

  2. #2

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    I ran into this issue when developing TRSPic and TRSWiki. My conclusion was that when doing anything using standard character graphics on the M4, it's best to run in M3 mode. It's also makes portability easier for having your program work across Models I/III/4.

  3. #3
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    Quote Originally Posted by steaminghacker View Post
    If this is true, is there any way to fix this?
    The Model 4 uses the same NTSC frequency as the Model III, so there simply aren’t enough lines to keep the same 8x12 character matrix when you up the number of lines from 16 to 24. NTSC has 262 lines per field, and you need to use at least 4 lines for the vertical sync pulse and some padding for a front/back porch, so the 240 lines the Model 4 outputs with its 24*10 lines is pretty much the max possible without running the monitor at an oddball frequency.
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  4. #4

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    This is terrible news!

    M3 mode will work, but then i wanted to make use of the extra columns for the M4 version.

    I guess my best plan is to redesign a new set of sprites for M4 so that they are, at least, symmetrical.

    I'm seeing 4 lines + 4 lines + 2 lines. Horrible!

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    If Radio Shack had cared about preserving the "pixel graphics" in Model 4 mode they could have done something like, I dunno, used 9 scanlines per character so the six sub-pixels were all an even 3 pixel talls for a total of 216 total lines. (This also would have had the advantage of staying closer to the 192 total lines of the Model III. It always kind of bugged me a little bit how the Model III mode of the Model 4 looked a little "squished" because need to re-tune the monitor to eliminate basically all the vertical overscan.) But at that point I think they'd pretty thoroughly decided the B&W TRS-80 line were "Business Computers" and graphics didn't matter.)
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  6. #6
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    Quote Originally Posted by Eudimorphodon View Post
    But at that point I think they'd pretty thoroughly decided the B&W TRS-80 line were "Business Computers" and graphics didn't matter.)
    ... or because it was so much easier to add hi-res graphics to the Model 4 (e.g. compared to the III).

  7. #7

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    Quote Originally Posted by gonk23 View Post
    ... or because it was so much easier to add hi-res graphics to the Model 4 (e.g. compared to the III).
    True, and the hires interface on the III/4 is pretty much identical and OS agnostic which helps from a portability perspective. But, you can't write a well-performing arcade type interactive game with the hires on a TRS-80. And if your application interface is using hires, then just develop and provide the program in M3 mode because there is no real advantage to performing the extra work to develop a M4 mode version at that point.

  8. #8
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    Yes, at different times during history of TRS80, Radio Shack did reduce size.

    This reduced costs, weight, size and shipping costs. It is always about money and larger pixels added a lot to costs and shipping weight.

    Bean counters had a formula to represent relationship between pixel size/weight to costs.

    Hope this helps.

  9. #9

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    Quote Originally Posted by danielbooneamerica View Post
    Yes, at different times during history of TRS80, Radio Shack did reduce size.

    This reduced costs, weight, size and shipping costs. It is always about money and larger pixels added a lot to costs and shipping weight.

    Bean counters had a formula to represent relationship between pixel size/weight to costs.

    Hope this helps.
    danielbooneamerica, I assume you intended to add a or similar to this post? That is a traditional way of stating your post is in jest. Otherwise, people may be confused.

  10. #10

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    Quote Originally Posted by pski View Post
    But, you can't write a well-performing arcade type interactive game with the hires on a TRS-80.
    I've been doing some investigation on this, to see if this is actually possible. Results so far don't look great tho'

    So the 10 scan lines per cell mean 24*10 = 240 which is why that's the same for the hi-res card. bandwidth?

    Presumably there's no way to define user characters on a standard M4? Otherwise here goes my attempt to make M4 sprites that don't look lumpy

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