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Thread: Wanted: 8086 mandelbrot generator?

  1. #1
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    Default Wanted: 8086 mandelbrot generator?

    I'm looking for a nice Mandelbrot drawer for DOS to demonstrate the awesome power of my 5140's several megahertz 8088 processor. It needs to support CGA. Does anyone know of one?

    Strangely even simtelnet is coming up dry --- there's plenty of 32-bit ones, some of which support CGA; and plenty of 16-bit ones, all of which require VGA. I can't find anything which combines CGA and 16-bit code (and no FPU).

    I'm really surprised; I was totally expecting to find a realtime Mandelbrot rotozoomer using CGA composite colours coming out of the demoscene...

  2. #2

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    I'm pretty sure Fractint will work on CGA and on an 8088. I don't think it will do 320x200 in 4 colors, but 640x200 in B&W works if memory serves me right...
    https://fractint.org/

  3. #3
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    Have you looked at Mandelbrot Magic? Claims to run on a PC with CGA and 256K of memory. 8087 isn't required, but is used if detected.

  4. #4
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    Seconding Fractint, it does CGA and even some more esoteric 8088/8086-era GPUs like the AT&T 6300 chipset.

  5. #5

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    Another vote for Fractint here - I had a lot of fun with that on the family Amstrad PC1512 as a child. It will do 320x200x4 as well as 640x200x2 (but not composite as far as I recall). It had the fastest Mandelbrot code I had seen at the time - just 30 seconds to draw the initial Mandelbrot was absolutely stunning compared to the multi-hour runs my own BASIC programs had been taking.

    Real-time Mandelbrot zooming seems to me to be a bit too ambitious for a 4.77MHz 8088 even using all the tricks of the demoscene - I don't think that feat was achieved until significantly faster CPUs were available. The problem is that plotting Mandelbrot sets requires doing a lot of multiplications, and a single signed 16-bit multiply on the 8088/8086 takes ~141 cycles. We might be able to do better than that by using the "difference of squares" method but we're still talking about seconds per frame rather than frames per second.

  6. #6
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    Quote Originally Posted by MrArgent View Post
    Seconding Fractint, it does CGA and even some more esoteric 8088/8086-era GPUs like the AT&T 6300 chipset.
    Small nitpick here:
    I often see the term 'GPU' these days to indicate any kind of video chip and/or board.
    This is not correct. CGA, EGA, VGA and related technologies do not quality as a GPU, since they are not processing units. They are merely logic arrays that can be controlled by the CPU, but they cannot perform any functions independently, let alone a sequence of functions. CGA does not even have any arithmetic capabilities at all. EGA and VGA have a very basic ALU that can only perform an action when the CPU issues a read or write of a VRAM address.
    The first common GPU was the NVIDIA GeForce. What made it a GPU is that it actually is a standalone processing unit, much like a CPU. That is, you can place a series of commands in its video memory (a 'program'), and the GPU will execute these completely independently to generate an image on screen.
    In fact, GPU was NVIDIA's marketing term. When ATi launched its competitor, they used the term VPU: Visual Processing Unit. It never caught on though.
    https://www.nvidia.com/page/geforce256.html
    NV's definition is very strict, and requires full 3D processing and a minimum performance guideline.

    (Although one could probably argue that certain older display adapters, such as the IBM PGC, or perhaps the Amiga with its copper/blitter combination, would also qualify to some extent. However, the term 'GPU' was not coined yet, so they were never referred to as such, so it would be an anachronism to do so).
    Last edited by Scali; May 5th, 2018 at 01:08 AM.

  7. #7
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    I'll admit to have having previously found Mandelbrot Magic, but found it almost completely impenetrable even after reading the documentation --- the UI would make SAP/Concur cry tears of joy.

    Regarding Fractint: I thought that it was 386 only (given that it started life as FRACT386), but you're right, apparently it's not. Unfortunately it's a 1.4MB executable which means I can't physically fit it onto one of the 5140's 720kB floppies!

    I actually ended up finding this 88-byte 16-bit boot sector Mandelbrot which uses integer-only arithmetic:

    http://blog.nothinguntoward.eu/?p=38

    It's monochrome EGA and uses 186 instructions, but it wasn't hard to modify. On my 5140, a 320x200 image takes four minutes to render.


  8. #8

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    Quote Originally Posted by hjalfi View Post
    Regarding Fractint: I thought that it was 386 only (given that it started life as FRACT386), but you're right, apparently it's not. Unfortunately it's a 1.4MB executable which means I can't physically fit it onto one of the 5140's 720kB floppies!
    Try one of the older ones available from https://fractint.org/ftp/archive/ . I remember using Fractint 15.1 from 5.25" 360kB floppies, despite the fact that FRACTINT.EXE was 384kB. I coaxed DOS into formatting an 80 track disk (even though it was only DSDD media in a 40 track drive). After track 41 or 42 the head was hitting its stop but cancelling at that point yielded a disk that DOS would attempt to write a larger file to. The last few kB of the exe were not written successfully but all the parts of the program I wanted to use worked fine (I think printing may have been broken but I could use an external program for that). Anyway, if you have a 720kB drive then you can probably use an even more recent version and won't have to resort to formatting trickery.

    The newer versions have more fractal types but I don't think they have any speed improvements for 8088 machines.

  9. #9
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    Quote Originally Posted by Scali View Post
    Small nitpick here:
    I often see the term 'GPU' these days to indicate any kind of video chip and/or board.
    This is not correct. CGA, EGA, VGA and related technologies do not quality as a GPU, since they are not processing units. They are merely logic arrays that can be controlled by the CPU, but they cannot perform any functions independently, let alone a sequence of functions. CGA does not even have any arithmetic capabilities at all. EGA and VGA have a very basic ALU that can only perform an action when the CPU issues a read or write of a VRAM address.
    The first common GPU was the NVIDIA GeForce. What made it a GPU is that it actually is a standalone processing unit, much like a CPU. That is, you can place a series of commands in its video memory (a 'program'), and the GPU will execute these completely independently to generate an image on screen.
    In fact, GPU was NVIDIA's marketing term. When ATi launched its competitor, they used the term VPU: Visual Processing Unit. It never caught on though.
    https://www.nvidia.com/page/geforce256.html
    NV's definition is very strict, and requires full 3D processing and a minimum performance guideline.

    (Although one could probably argue that certain older display adapters, such as the IBM PGC, or perhaps the Amiga with its copper/blitter combination, would also qualify to some extent. However, the term 'GPU' was not coined yet, so they were never referred to as such, so it would be an anachronism to do so).
    Ah. I've always sort of retroactively dubbed any graphics/vdp/crtc hardware a GPU as a matter of phrase familiarity. I didn't know there was any specific marketing-related connotations to the phrase offhand - thanks!

  10. #10
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    I didn't find MM that confusing. I briefly skimmed the manual and loaded up a set. All under DOS emulation on Linux:mbrot.jpg

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