🚀 go-pugleaf

In article <7cbvvv$9oc$1@winter.news.rcn.net>,
  Samir Wyszynski <samirw@connection.com> wrote:
> black_phantom@my-dejanews.com wrote:
> > =
>
> >   "TK - TBD" <PISS_OFF_SPAMMERS_Thomas_Kjoernes@phoenix.com> wrote:
> > > tunney <bigmacmeal@hotmail.com> wrote in article
> > > <7c6u0d$cue$1@winter.news.rcn.net>...
> > > > I know that this is a thick question, but could someone explain to =
> me
> > > > how to clear the screen in text and video mode, can't for the life =
> of me
> > > > figure out how. Please help me I have an exam in this soon.
> > > > Also could someone explain int 21h service 0Ah
> > > >
> > > > Thanks a million.
> > >
> > > Clearing the screen (TEXTMODE) is easy:
> > >
> > > mov ax, 3     ; set mode 3, voil=E0 screen is cleared.
> > > int 10h               ;
> > >
> > > For less flickering... you could clear it by filling video mem
> > > directly, like this:
> > >
> > > push 0B800h
> > > pop es
> > > xor ax, ax
> > > xor di, di
> > > mov cx, 16384
> > > rep stosw
> > >
> > > For video mode, ask someone else.
> > =
>
> > I think it should be "graphics" mode, not "video" mode. It's not a lot =
> harder.
> > For CGA graphics modes the above will also work. For chained modes (MCG=
> A 13h)
> > you clear 64k starting at 0A0000h:
> > =
>
> > clear_a0000:
> > mov ax, 0A000h
> > mov es, ax
> > sub ax, ax
> > sub di, di
> > mov cx, 32768
> > cld
> > rep stosw
> > =
>
> > For non-chained modes the above clears only bit plane selected in seque=
> ncer.
> > To clear screen you need to allow write to all 4 bit planes:
> > =
>
> > mov dx, 3c4h
> > mov ax, 0F02h
> > out dx, ax
> > =
>
> > Of course, it's a good idea to save previous bit plane write bitmask an=
> d later
>
> > That's all for standard VGA BIOS modes. I hope that you don't need to d=
> eal
> > with non-standard modes ('X' or how is it called now?) - it's no harder=
>  just
> > more dirty work.
> > =
>
> What do you mean nonstandard - the 32K 64K and true color where each
> pixel is described by 2 or 3 consecutive bytes? =

  Bit planes can be grouped in bytes rather than bits. Memory can be mapped
in defferent ranged between A0000h and BFFFFh. Bit planes can be accessed in
couples (odd/even modes) - that's what happens in text modes in fact. That's
all only standerd VGA; non-standard adapters can have 8 and more bit planes.
All those and other possibilities can be checked via VGA registers but I'd
rather support only standard BIOS modes.

>
> I was exited about planar video memory on Amigas when they first came
> out, and all I had was 4 color Commodore 64 but soon after I realized
> that it is very awkward to handle.
> Personaly I thing the new modes are much more elegant way of handling
> the display. There is no need to access 4 different locations while
> switching banks. Most high res VGAs have vesa BIOS or it is available as
> a TSR.
> Piece of cake.
>

-- Sclerosis cannot be healed but can be forgotten --

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