> -----Original Message-----
> From: M100 [mailto:[email protected]] On Behalf Of
> [email protected]
> Sent: Thursday, January 21, 2021 01:47
> To: [email protected]
> Subject: Re: [M100] vga monitor solutions
>
> CAUTION External Sender: Do not click links or open attachments unless
> you recognize the sender and know the content is safe.
>
>
> Hi,
>
> The web site at
>
> https://can01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgeoffg
> .net%2Fterminal.html&data=04%7C01%7CJim.Anderson%40kpu.ca%7C243eac70
> cb824a29a06f08d8bdf1744b%7C66b9f62d3042495eaab6db86f21500c0%7C0%7C0%7C63
> 7468192055341328%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2l
> uMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=B1ltiTld1tcwIf1LmP6
> 3MUhFIk%2FGWLo7Vo6Xs8TIqrI%3D&reserved=0
>
> says
>
> Graphics resolution is 480x288 pixels in VGA 25 line mode, 480x432
> pixels in VGA 36 line mode, 288x216 in PAL composite and 264x180 pixels
> in NTSC composite mode
>
> but maybe that's not the whole story.
AFAIK it's outputting a signal at the 640x480 scan rate, but seems to be
leaving some underscan space at least at the top and bottom, probably also the
sides but it may also not be modulating the horizontal signal as fast as would
be necessary to get 640 pixels across.
FYI the 480x288 figure is a bit misleading - for one thing, that's the
resolution you have available to address when using extended line/box/circle
drawing graphics codes. For another, it is always drawing the characters using
480x432 pixels whether you're in 24-line mode or 36-line mode, it's just that
in order to simplify things Geoff Graham (the original designer of the board
the MVT100 is based on) used the same font bitmap for both modes and
implemented a very simple 2:3 scaling mechanism for 24-line mode (every 3rd
scanline is a repeat of the one before it).
That's one of the reasons the font doesn't look great (why the middle element
of the H is so thick, or why X looks so weird, among many other things). The
other contributing factor for most people is that they're displaying it on an
LCD monitor which has to scale up from the 640x480 output signal. Even if you
have a modern OS output a 640x480 signal onto an LCD monitor, text is going to
look terrible because of the scaling. On a CRT monitor, it looks much better
because it doesn't have to try to map signal pixels onto discrete display
elements.
I started out offering Stephen a hand with creating the M100-specific extended
character bitmaps for the MVT100 firmware, but while I was at it I modified a
couple of the existing characters to make them easier to read (in particular, I
found the original shapes of 6 and 9 to be difficult to distinguish from 8, for
instance, and Q was just weird). In the process of creating the bitmaps for
the extended character set I realized Geoff's code was scaling up the font in a
non-linear manner because weird things were happening (I wasn't getting
on-screen exactly what I defined in the bitmap).
Because I'm a bit OCD and the font thing is bugging me, I'm making further
modifications to improve the appearance of the text (defining a clean font for
it to use in 24-line mode rather than scaling up the font used in 36-line
mode), and while I was at it I started to wonder about the odd shape of some of
the characters and whether it would be truer to the purpose of the MVT100 board
to model the characters after the font used in the DVI instead of sticking with
Geoff's characters.
I haven't seen the actual DVI display, though, so maybe that font is actually
worse? :)
jim
