Hi guys,
/* increment our line if paginating, display message at end of screen */
static int incline(void) {
if (!optP) return E_None;
if (++line >= MAX_Y) {
line = 0;
return pause();
}
return 0;
}
Now the obvious question of course is "what is MAX_Y?". And one grep
later, I've got the answer:
$ grep 'MAX_Y' -R *
cmd/dir.c: if (++line >= MAX_Y)
include/misc.h:#define MAX_Y (*(unsigned char far*)MK_FP(0x40, 0x84))
include/misc.h:#define SCREEN_ROWS (MAX_Y + 1)
(...)
Yes, I've also run into such phenomenon although in that case, the screen
_width_ was zero by buggy BIOS.
The Drivers unit in Borland Pascal's Turbo Vision fetches the screen
height like this (comments by me), SetCrtData() is to be called:
[...]
{ Save registers and call video interrupt }
procedure VideoInt; near; assembler;
asm
PUSH BP ; save registers that are destroyed in buggy BIOS'es
PUSH ES
INT 10H
POP ES
POP BP
end;
{ Return CRT mode in AX and dimensions in DX }
procedure GetCrtMode; near; assembler;
asm
MOV AH,0FH ; "get current video mode" function
CALL VideoInt ; video mode in AL, screen width in AH
PUSH AX
MOV AX,1130H ; "get font information" function
MOV BH,0 ; request for arbitrary pointer
MOV DL,0 ; pre-load with default value
CALL VideoInt ; last row number in DL
POP AX
MOV DH,AH ; screen width in DH
CMP DL,25 ; for more than 25 rows, hires screen is
SBB AH,AH ; marked in high byte of video mode
INC AH
end;
{ Set CRT data areas and mouse range }
procedure SetCrtData; near; assembler;
asm
CALL GetCrtMode
MOV CL,1 ; by default, hires screen
OR DL,DL
JNE @@1 ; for an invalue last row number of 0,
MOV CL,0 ; correct to to lores screen and last row
MOV DL,24 ; number of 24
@@1: INC DL ; convert last row number to screen height
MOV ScreenMode,AX ; store video mode, screen width/height,
MOV ScreenWidth,DH ; hires/lores screen
MOV ScreenHeight,DL
MOV HiResScreen,CL
XOR CL,1 ; set hires screen as non-snowing, lores
MOV BX,SegB800 ; as snowing, set color video segment
CMP AL,smMono
JNE @@2
MOV CL,0 ; for mono mode, non-snowing, set mono
MOV BX,SegB000 ; video segment
@@2: MOV CheckSnow,CL ; dis-/enable snow checking
[...]
The whole point is that CGA's (that need snow checking) can be detected
exactly by the invalid last row number of 0.
Joe
--
KOVÁCS Balázs alias Joe Forster/STA s...@c64.org; http://sta.c64.org
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