Hi Tom,
>
> > The only reliable way is to trap int10, write a character using int21 and
> > see if it gets trapped.
>
> I've seen (N)ANSI.SYS implementations doing direct screen IO.
You're quite right about that so this is not good.
> however: talking about CLS, why not
>
> 1'st) write ESC J (or similar)
> 2'nd) clear the screen, using BIOS.
>
> ALL screens will be blank then - as intended.
No, if the output goes to COM1 and not CON then the screen should be
cleared on COM1 and not CON.
Keep it simple, checking two bits ought to be enough:
ax=4400, bx=1, int21
if (ax & 0x80) /* device */
if (ax & 0x10) /* fastcon */
use bios (int10)
else
use escape sequences
else /* file */
do nothing
MS COMMAND.COM actually does:
INT2F at 8d5e:3397: AX=1a00, BX=3391, CX=0000, DX=867e, DS=8d5e, ES=8d5e
INT21 (0) at 8d5e:33aa: AX=440c, BX=0001, CX=037f, DX=db6f, DS=8d5e,
INT21 (0) at 8d5e:33c0: AX=4400, BX=0001, CX=037f, DX=db6f, DS=8d5e,
INT10
(see also my previous email what happens if you clear the fastcon bit)
But NANSI.SYS doesn't support int2f/AX=1a00 or the device driver ioctl
corresponding to 440C, so the first two aren't that important -- on a
local display we can use int10 anyway.
Bart
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