Atari 400 Technical Reference Manual page 203

B15 LOGCOL* [0063, lJ -- Cursor/logical line column number
LOGCOL contains the logical-line column number for the current
cursor position; note that a logical line can comprise up to
three
ph~sical
lines. This variable is for the internal use of
the Display Handler.
Split Screen
The Displav Handler and Screen Editor together support the
operation of a split-screen mode (see Section 5) in which the main
portion of the screen is in one of the graphics modes and is
controlled b~
the Display Handler, and there are 4
ph~sical lines in
the text window at the bottom of the screen which is controlled b~ the
Screen Editor.
B16 BOTSCR* [02BF, lJ -- Text screen lines count
BOTSCR contains the number of lines of text for the current
screen: 24 for mode 0 or 4 for a split-screen mode.
The Handler
also uses this variable as an indication of the split-screen
status; tests are made for the specific values 4 and 24.
DRAW/FILL Function
The DRAW function line drawing algorithm is shown below
translated to the PASCAL language from assembly language.
218
NEWROW
-
ROWCRS; NEWCOL
: =
COLCRS;
DEL TAR
. =
ABS ( NEWROW-OLDROW ) ;
ROW INC
.=
SIGN (NEWROW-OLDROW) ; {
+1
DELTAC
-
ABS (NEWCOL-OLDCOL) ;
COL INC
-
SIGN ( NEWC OL -OLDC OL )
i
{ +1
ROWAC
:= 0;
COLAC
:= 0;
ROWCRS OLDROWi COLCRS
:=
OLDCOLi
COUNTR := MAX (DELTAC,DELTAR);
ENDPT := eOUNTRi
IF COUNTR
=
DELTAC
THEN ROWAC ENDPT DIV
2
ELSE eOLAC
:=
ENDPT DIV 2;
WHILE COUNTR
>
0 DO
BEGIN
or -1 }
or -1
}
OPERATING SYSTEM C016555 -- Appendix L