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Type: Posts; User: reenigne

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    Thanks! Yes, I have a lot of plans for it (more...

    Thanks! Yes, I have a lot of plans for it (more plans than time at the moment). Eventually I hope that it will be a full-fledged graphics editor as well as converter and renderer, and (as previously...
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    Yes, turn down "quality" (I think it should work...

    Yes, turn down "quality" (I think it should work with quality set to 0, the fastest setting). I previously thought quality 1 was needed when really it was a 640x200 input image that was needed.

    I...
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    Ah, I wondered if it might be something like...

    Ah, I wondered if it might be something like that. I'm pretty sure this is not going to work on CGA (at least one based on a 6845). Changing the start address on a 6845 only takes effect at the...
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    These links give me "invalid attachment...

    These links give me "invalid attachment specified". Are you talking about cgacal.png? (I thought by 320x200 you meant a 320x200x4 graphics mode image but there wasn't one of those in your archive)....
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    Can you show me the image that you're having...

    Can you show me the image that you're having trouble with?
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    That sounds like you're converting an image in a...

    That sounds like you're converting an image in a graphics mode, but using a value of 1 instead of 2 for scanlines per row. The image will look the same in CGAArt, but the memory format is different.
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    Ah, looks like I have a bug in the prescaler. If...

    Ah, looks like I have a bug in the prescaler. If you resize the screenshots to 640x200 in another program first (using nearest-neighbour scaling) then everything works. I will look into fixing this...
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    That's right. The CGAD format can represent...

    That's right. The CGAD format can represent mid-frame (and even mid-line) palette/background/mode changes but the current version of CGADView won't display them and the current version of CGAArt...
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    I have written something very similar to what you...

    I have written something very similar to what you describe (although my format is slightly more complicated). http://www.reenigne.org/misc/cgadview.zip . CGAArt...
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    Yes, you can do that. You can even disable the...

    Yes, you can do that. You can even disable the keyboard interrupt altogether via the mask register on the PIC. See lines 255-258 and 623-636 of...
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    Whoops, you're absolutely right. It's 18.432kHz...

    Whoops, you're absolutely right. It's 18.432kHz for MDA. I'm not sure where the 18.73kHz came from. EGA's mono mode (BIOS mode 0x0f) is also an (MDA compatible) 18.432kHz mode, and both EGA and MDA...
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    I find it helps to come up with some terminology...

    I find it helps to come up with some terminology for the various different time units of importance (thus avoiding confusion about exactly what "dot clock" you're talking about). The ones I use (I...
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    Do you know if any real software actually used...

    Do you know if any real software actually used "POP CS" or "MOV CS,rmw"? As well as being invalid after 8086, they also have the problem that they don't clear the prefetch queue, which means the next...
  14. How about INT 21h function 44h (IOCTL) with AL=8...

    How about INT 21h function 44h (IOCTL) with AL=8 (Device Removable Query)? I think this will return CF=1 if the drive letter doesn't exist. Ultima VI (when run on DOS 3.0+) will enumerate over all 26...
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    The patterns are nice but the colour reproduction...

    The patterns are nice but the colour reproduction isn't very accurate. It doesn't look like you're doing any kind of gamma correction, which may be part of this. It also looks like you're not taking...
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    It's definitely a problem with the CGA card. And...

    It's definitely a problem with the CGA card. And a really interesting one too! I'm scratching my head trying to figure out what failure could cause that particular pattern. It looks like something to...
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    I think that should work too. Intrigued to...

    I think that should work too.



    Intrigued to see what the application is!
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    You'll want to look at the source code of...

    You'll want to look at the source code of Fractint - that supports a lot of tweaked modes on standard VGA up to and including 800x600. It was also popular enough that the timings were probably tuned...
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    Yep, that's the one I was trying to point to!...

    Yep, that's the one I was trying to point to! Sorry for the copy/paste failure.



    Depends what you're doing! But I can't imagine that changing the clocking mode is something you're going to be...
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    There was a good thread...

    There was a good thread on this a few years ago. VGA wasn't mentioned specifically though. I'm fairly sure that the extra delays are never necessary when accessing VGA registers. One reason is that...
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    Perhaps that particular routine doesn't care...

    Perhaps that particular routine doesn't care about preserving the contents of VRAM, and therefore uses the faster asynchronous reset. Or (because it's tied to a particular piece of VGA hardware) it...
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    Well yes, standard VGA text mode is 720x400 at...

    Well yes, standard VGA text mode is 720x400 at 70Hz so that's not too surprising. But the video bandwidth requirements for text mode and 16 colour graphics modes are less than that of 256 colour...
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    Btw, if you used the 28.322MHz clock then you'd...

    Btw, if you used the 28.322MHz clock then you'd get up to 44.3Hz.



    The DRAM chips on my original IBM VGA card are 41464C-12. This has a minimum access cycle time of 220ns, which works out as...
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    Ooo let's see... Pixel clock of 25.175MHz divided...

    Ooo let's see... Pixel clock of 25.175MHz divided by 8*(0xad + 5)*(0x1bf + 2) == 39.37Hz. You'd need a good supply of ibuprofen as well as the multisync!
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    The missing piece of the puzzle here is memory...

    The missing piece of the puzzle here is memory bandwidth. If IBM had created a VGA card with 128kB (half as many DRAM chips) then the amount of data that can be transferred out of VRAM and onto the...
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