Writing text to screen border possible? 
Author Message
 Writing text to screen border possible?

        One can change the color of the border outside the normal screen
text area with INT 10h, AX=1001h.  However, I have seen no reference to
any way to write text to this border area (which would be a useful place
to display output from a TSR clock, for example, without overwriting any
of the background program's text).  Is it possible to do this?

                                                        --Donald Davis



Fri, 27 Aug 1999 03:00:00 GMT  
 Writing text to screen border possible?

Quote:
>    One can change the color of the border outside the normal screen
>text area with INT 10h, AX=1001h.  However, I have seen no reference to
>any way to write text to this border area (which would be a useful place
>to display output from a TSR clock, for example, without overwriting any
>of the background program's text).  Is it possible to do this?

>                                                    --Donald Davis

As a TSR? No, this would require using interrupts (timer) on which you
can't rely not to be changed.

You need to add an extra text line to the bottom of the screen (with
the crtc registers) to put your clock in. However, the data which
would be used to display that extra text line would be partially in
the range of the next page. As a TSR you can't rely on that next page
not to be used. So that option is out of the question (you could put
it to the far left but you would also see the data of the next page on
the right)

You could use the line compare register to get the data out of the
first line of page 0 but it would require some timing to have it set
and restored before it's being used to display the top line again.
This timing should be done by timer interrupts on which you cannot
rely to be free for use (a program could disable interrupts or use the
timer itself).

  "A compiler that generates better code than a good
   assembly programmer? That'll be the day."
  (Michael Abrash)




Sat, 28 Aug 1999 03:00:00 GMT  
 Writing text to screen border possible?


Quote:
>    One can change the color of the border outside the normal screen
>text area with INT 10h, AX=1001h.  However, I have seen no reference to
>any way to write text to this border area (which would be a useful place
>to display output from a TSR clock, for example, without overwriting any
>of the background program's text).  Is it possible to do this?

I guess if you could get the timing accurate enough (will be plagued
by interrupt latency etc), you could draw the text by changing the
colours from black to white rapidly.  People even managed this on the
zx spectrum, but the resolution was quite poor (4 pixels).

Jim



Sat, 28 Aug 1999 03:00:00 GMT  
 Writing text to screen border possible?


Quote:

>    One can change the color of the border outside the normal screen
>text area with INT 10h, AX=1001h.  However, I have seen no reference to
>any way to write text to this border area (which would be a useful place
>to display output from a TSR clock, for example, without overwriting any
>of the background program's text).  Is it possible to do this?

One simple answer: No. Forget it.
---
Feico Nater, Netherlands
---
In matters of trade the fault of the Dutch
is offering too little and asking too much.


Sat, 28 Aug 1999 03:00:00 GMT  
 Writing text to screen border possible?

Quote:

>         One can change the color of the border outside the normal screen
> text area with INT 10h, AX=1001h.  However, I have seen no reference to
> any way to write text to this border area (which would be a useful place
> to display output from a TSR clock, for example, without overwriting any
> of the background program's text).  Is it possible to do this?

Simply put, no.  That area is the overscan, and the overscan is
controlled by the timing registers.  For vertical size, it's controlled
by the Vertical Display End register, the Start Vertical Blanking
register, and the End Vertical Blanking register.  The horizontal size
is controlled by the Horizontal Display End register, the Start
Horizontal Blanking register, and the End Horizontal Blanking register.

That area doesn't have any actual memory mapped to it, so I doubt it's
even possible to put anything there than a solid color (as determined by
the overscan register).

Quote:
>                                                         --Donald Davis

--
Scott Earnest        | We now return you to our regularly |



Sat, 28 Aug 1999 03:00:00 GMT  
 Writing text to screen border possible?


Quote:

>        One can change the color of the border outside the normal screen
>text area with INT 10h, AX=1001h.  However, I have seen no reference to
>any way to write text to this border area (which would be a useful place
>to display output from a TSR clock, for example, without overwriting any
>of the background program's text).  Is it possible to do this?

No. There is no memory associated with the area, it's just scanned with a color
turned on.

--

leading x here and in the header (too much offensive junk mail))



Sat, 28 Aug 1999 03:00:00 GMT  
 Writing text to screen border possible?

Quote:

> >       One can change the color of the border outside the normal screen
> >text area with INT 10h, AX=1001h.  However, I have seen no reference to
> >any way to write text to this border area (which would be a useful place
> >to display output from a TSR clock, for example, without overwriting any
> >of the background program's text).  Is it possible to do this?

Not really. But maybe there is a way to tweak a text mode with a few
extra rows and columns and trick programs into using an 80x25 subset ?
But thats not an easy task if it is possible at all with programs
writing directly to video memory and all ...

   __/  __/   -  Christian Froeschlin
  /    /
 /     _/     * If you eliminate the impossible, whatever remains, *
___/ _/       * however improbable, must be the BUG !              *



Sun, 29 Aug 1999 03:00:00 GMT  
 Writing text to screen border possible?


:       One can change the color of the border outside the normal screen
: text area with INT 10h, AX=1001h.  However, I have seen no reference to
: any way to write text to this border area (which would be a useful place
: to display output from a TSR clock, for example, without overwriting any
: of the background program's text).  Is it possible to do this?

Nope.  That is an overscan area, the video card does not fetch characters
while displaying in that area.  Although you could possibly put the
thing in some graphics mode and make the overscan smaller so you can put text
there...

David
:
:                                                       --Donald Davis



Sun, 29 Aug 1999 03:00:00 GMT  
 Writing text to screen border possible?


   >Newsgroups: comp.os.msdos.programmer,comp.lang.asm.x86

   >I guess if you could get the timing accurate enough (will be plagued
   >by interrupt latency etc), you could draw the text by changing the
   >colours from black to white rapidly.  People even managed this on
   >the zx spectrum, but the resolution was quite poor (4 pixels).
   >Jim

   A point of note: You cannot get the timing accurate enough, nor can you
actualy perform the OUT's fast enough to use this technique on a PC.

   although this sorta technique would be good to simulate something like the
the Apple IIgs 3200 color graphics mode, the IIgs could update the entire
palette (16 colors) at each scanline in 320x200 mode.

   16 colors per line, 200 lines .. 3200 colors. It actualy was quite
impressive since at the time lousy EGA was all the rage on PC's =)


--: COMPUTERVREDEBREUK

Net-Tamer V 1.08 - Test Drive



Sun, 29 Aug 1999 03:00:00 GMT  
 Writing text to screen border possible?

Quote:


>   >Newsgroups: comp.os.msdos.programmer,comp.lang.asm.x86

>   >I guess if you could get the timing accurate enough (will be plagued
>   >by interrupt latency etc), you could draw the text by changing the
>   >colours from black to white rapidly.  People even managed this on
>   >the zx spectrum, but the resolution was quite poor (4 pixels).
>   >Jim

>   A point of note: You cannot get the timing accurate enough, nor can you
>actualy perform the OUT's fast enough to use this technique on a PC.

>   although this sorta technique would be good to simulate something like the
>the Apple IIgs 3200 color graphics mode, the IIgs could update the entire
>palette (16 colors) at each scanline in 320x200 mode.

>   16 colors per line, 200 lines .. 3200 colors. It actualy was quite
>impressive since at the time lousy EGA was all the rage on PC's =)

It's a shame that :-(  It was just an idea.  On the inner screen it's
easy to change the colour quickly (but not particularly accurately) -
exactly how many out's (etc) would be needed to change the colours in
the border area?

Jim



Mon, 30 Aug 1999 03:00:00 GMT  
 Writing text to screen border possible?

Quote:

> I guess if you could get the timing accurate enough (will be plagued
> by interrupt latency etc), you could draw the text by changing the
> colours from black to white rapidly.  People even managed this on the
> zx spectrum, but the resolution was quite poor (4 pixels).

> Jim

On most new monitors, it's possible to adjust the screen image so that
there is practically no screen border showing.  Certainly there would be
little room for any text there anyway.

-- Michael Best



Mon, 30 Aug 1999 03:00:00 GMT  
 Writing text to screen border possible?

James Shaw:

Quote:
> It's a shame that :-(  It was just an idea.  On the inner screen it's
> easy to change the colour quickly (but not particularly accurately) -
> exactly how many out's (etc) would be needed to change the colours in
> the border area?

  On the VGA?  It's just one, isn't it?  I think you can also switch banks
of 16 colours (in 16 colour mode) in one port, as well..


Sat, 04 Sep 1999 03:00:00 GMT  
 Writing text to screen border possible?

Quote:

> James Shaw:
> > It's a shame that :-(  It was just an idea.  On the inner screen it's
> > easy to change the colour quickly (but not particularly accurately) -
> > exactly how many out's (etc) would be needed to change the colours in
> > the border area?

>   On the VGA?  It's just one, isn't it?  I think you can also switch banks
> of 16 colours (in 16 colour mode) in one port, as well..

I'm not sure off the top of my head about color bank switching, but I
*do* know that setting the overscan register will require a few port
calls.

1 IN to reset the attribute controller flip-flop
1 OUT to set the address (16h)
1 OUT to write the color to the overscan register
1 OUT to return palette control to the video hardware

That's 4 ports by my reckoning.  :-)

Actually, the color banks may also be controlled in the attribute
controller registers, so it will probably be about the same, or
depending on how it's handled, more.

--
Scott Earnest        | We now return you to our regularly |



Sat, 04 Sep 1999 03:00:00 GMT  
 Writing text to screen border possible?



Quote:

>> >       One can change the color of the border outside the normal screen
>> >text area with INT 10h, AX=1001h.  However, I have seen no reference to
>> >any way to write text to this border area (which would be a useful place
>> >to display output from a TSR clock, for example, without overwriting any
>> >of the background program's text).  Is it possible to do this?

>Not really. But maybe there is a way to tweak a text mode with a few
>extra rows and columns and trick programs into using an 80x25 subset ?
>But thats not an easy task if it is possible at all with programs
>writing directly to video memory and all ...

Well considering that Windows runs such programs in a window it is
surely possible. One can set the adapter into 90x25 or 80x28 mode. In
the latter the three last lines might be relatively easy to use for
other purposes. (Just cheat the bios by telling that there are only 25
lines?). Of course programs that tried to use more than 25 rows could
cause problems.

Osmo



Sat, 04 Sep 1999 03:00:00 GMT  
 Writing text to screen border possible?

Quote:

> No. There is no memory associated with the area, it's just scanned with a color
> turned on.

I wonder how they did it on an Atari ST. I've seen a scroller in the
overscan. It was also possible (like the IIgs) to grab the HBL and
change the palette to fake 256 colour mode from 16 colours.

cheers
Dan

--
-- Dan Glastonbury, Software Resource Engineer      _--_|\
-- Motorola Australia Software Centre              / MASC \
-- 2 Second Avenue, Technology Park Adelaide 5095  \_.-*._/
-- Tel: +61 8 8203 3644, Fax: +61 8 8203 3501            v  



Sun, 05 Sep 1999 03:00:00 GMT  
 
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