Atari 400 Technical Reference Manual page 381

ERR LINE ADDR B1 B2 B3 B4 DISPLAY HANDLER
-- 10-30-78 -- DISPLC PAGE 120
5383
. PAGE
5384
5385
5386
;
DRAW -- DRAW A LINE FROM OLDROW,OLDCOL TO NEWROW,NEWCOL
5387
;
(THE AL MILLER METHOD FROM BASKETBALL)
5388 FCFC A2 00 DRAW: LDX #0
5389
FCFE
A5 22 LDA ICCOMZ ; TEST COMMAND: $ll=DRAW $12=FILL
5390 FDOO C9 11 CMP #$11
5391 FD02 FO 08 BEG DRAWA
5392 FD04 C9 12 CMP #$12
j
TEST FILL
5393 FD06 FO 03 BEG DRAWB
; YES
5394 FD08 AO 84 LDY #t\NALID
j
NO, SO RETURN INVALID COMMAND
5395
FDOA
60 RTS
5396 FDOB E8 DRAWB: INX
5397 FDOC 8E B7 02 DRAWA: STX FILFLG
5398 FDOF A5 54 LDA ROWCRS iPUT CURSOR INTO NEWROW,NEWCOL
5399 FDll 85 60
STA
NEWROW
5400 FD13 A5 55 LDA COLCRS
5401 FD15 85 61 STA NEWCOL
5402 FD17 A5 56 LDA COLCRS+1
5403 FD19 85 62 STA NEWCOL+1
5404 FD1B A9 01 LDA #1
5405 FDID 85 79 STA ROW INC
iSET UP INITIAL DIRECTIONS
5406 FDIF 85 7A STA COL INC
5407 FD21 38 SEC
5408 FD22
A5 60 LDA NEWROW iDETERMINE DELTA ROW
5409 FD24
E5 5A SBC
OLDRQW
5410 FD26
85 76 STA DEL TAR
5411 FD28 BO OD BCS DRAWl
iDO
DIRECTION AND ABSOLUTE VALUE
5412 FD2A A9 FF LDA #$FF iBORROW WAS ATTEMPTED
5413 FD2C 85 79 STA ROWINC iSET DIRECTION=DOWN
5414 FD2E A5 76 LDA DEL TAR
5415 FD30 49 FF EOR #$FF iDELTAR = IDELTARI
5416 FD32 18 CLC
5417 FD33 69 01 ADC #1
5418 FD35 85 76
STA DEL TAR
5419 FD37
38
DRAWl:
SEC
5420 FD38
A5 61 LDA NEWCOL iNOW DELTA COLUMN
5421 FD3A E5 5B SBC OLDCOL
5422 FD3C 85 77 STA DELTAC
5423 FD3E A5 62
LDA
NEWCOL+l
iTWO-BYTE GUANTITY
5424 FD40
E5 5C SBC OLDCOL+1
5425 FD42
85 78 STA DELTAC+l
5426
FD44
BO 16 BCS DRAW2 iDIRECTION AND ABSOLUTE VALUE
5427 FD46 A9 FF LDA #$FF iBORROW WAS ATTEMPTED
5428 FD48 85 7A STA COLINC iSET DIRECTION = LEFT
5429 FD4A A5 77 LDA DELTAC
5430 FD4C 49 FF EOR #$FF iDELTAC = IDELTACI
5431 FD4E 85 77 STA DELTAC
5432 FD50 A5 78 LDA DELTAC+1
5433 FD52 49 FF
EOR
#$FF
5434 FD54
85 78 STA DELTAC+l
5435 FD56 E6 77 INC DELTAC
iADD ONE FOR TWOS COMPLEMENT
5436 FD58 DO 02 BNE DRAW2