Which function handles copying into the video ram?

Which function handles copying into the video ram?

[Ingo Brueckl]

Hi,

I have an old DOS programm that runs fine with dosemu, but the output of a
few characters is strange due to some reasons that aren't important to the
problem.

I assume that the program does its video output by copying directly into the
vga graphics memory (text mode), because it is (and always was) very speedy.

What I'd like to do now: If the programs is going to copy some certain
characters with some certain color attribute to the screen, I want to change
the character, e. g. I need to hook into the dosemu function that is called
for 'copying into the video ram'.

Could someone please tell me where I can find this function and what its name
is?

Thank you very much.

Re: Which function handles copying into the video ram?

[Bart Oldeman]

2009/5/28 Ingo Brueckl <ib@wupperonline.de>:
> I assume that the program does its video output by copying directly into the
> vga graphics memory (text mode), because it is (and always was) very speedy.
>
> What I'd like to do now: If the programs is going to copy some certain
> characters with some certain color attribute to the screen, I want to change
> the character, e. g. I need to hook into the dosemu function that is called
> for 'copying into the video ram'.
>
> Could someone please tell me where I can find this function and what its name
> is?

Perhaps you are looking for
src/env/video/text.c
static void draw_string(int x, int y, char *text, int len, Bit8u attr)

In this file are the routines that read the video ram. But DOS
programs just write into the video ram directly, there is no DOSEMU
routine involved there, it's just a chunk of memory that DOSEMU reads
at intervals to update the screen.

Bart

Which function handles copying into the video ram?

[Ingo Brueckl]

Bart Oldeman writes:

 > But DOS programs just write into the video ram directly, there is no
 > DOSEMU routine involved there, it's just a chunk of memory that DOSEMU
 > reads at intervals to update the screen.

I see. Now I understand why I couldn't find a routine to hook in.

 > Perhaps you are looking for
 > src/env/video/text.c
 > static void draw_string(int x, int y, char *text, int len, Bit8u attr)

This is exactly what I was looking for!

Thank you so very much for your kind help.

I could now make the desired screen output manipulation making my old dos
editor to run with dosemu under Linux as if it were written for Linux.

Again, thanks a lot.

Ingo

Which function handles copying into the video ram?

[Ingo Brueckl]

Manfred Scherer wrote:

 > maybe function tty_char_out() is the right place for your hook:

No, unfortunately it isn't. I already checked this, and output isn't done
there.

BTW, what I forgot to mention: I'm talking from xdosdemu, e. g. the program
runs in a X window (if that matters).

Ingo

Re: Which function handles copying into the video ram?

[Manfred Scherer]

Hi Ingo,

maybe function tty_char_out() is the right place for your hook: 

src/base/bios/int10.c
void tty_char_out(unsigned char ch, int s, int attr)


Manfred