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drawline.asm
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Assembly Source File
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1983-07-27
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5KB
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150 lines
PAGE,132
PUBLIC DRAWLINE
; DAN ROLLINS (213) 246-5021
;
;8088 self-modifying program implements fast-vector algorithm
;described by Michalsky, Doctor Dobb's Journal #74, 12/82
;see also: FAST-LINE DRAWING TECHNIQUE, BYTE, Aug 81
;
;routine expects to be called with DS:SI pointing
;to a list of 2-byte arguments:
;
; si+0 = x1 starting clm (0-319)
; si+2 = y1 starting row (0-159)
; si+4 = x2 ending clm
; si+6 = y2 ending row
; si+8 = color (0,1,2,3)
; si+10 = length
; 0 = draw entire line
; else = draw sub- or super-set of this vector
; si+12 = skip length
; number of pels to go before starting to draw
; 0 = draw entire line
;destroys all registers execpt si and segment regs
code group cseg
cseg segment public 'code '
assume CS:cseg,DS:nothing,ES:nothing
;make it easier to acceess variables and arguments
x1 equ word ptr [si]
y1 equ word ptr [si+2]
x2 equ word ptr [si+4]
y2 equ word ptr [si+6]
color equ byte ptr [si+8]
len equ word ptr [si+10]
skip equ word ptr [si+12]
;these are values that will be overlayed in the code
INC_X EQU 41H
DEC_X EQU 49H
INC_Y EQU 42H
DEC_Y EQU 4AH
;these are the addresses where new code is overlayed
ADJ_LONG_AXIS EQU BYTE PTR CS:[DI]
ADJ_MASTER EQU WORD PTR CS:[DI+3]
TEST_MASTER EQU WORD PTR CS:[DI+7]
ALT_ADJ_MASTER EQU WORD PTR CS:[DI+13]
ADJ_SHRT_AXIS EQU BYTE PTR CS:[DI+15]
DRAWLINE PROC FAR
MOV BL,INC_X ;ASSUME XSTEP = +1
MOV AX,X2
SUB AX,X1
JGE DL1 ;IF X1 <= X2 THEN NO CHANGE
MOV BL,DEC_X ;XSTEP = -1
NEG AX ;Xdist = ABS(Xdist)
dl1:
MOV CX,AX ;SAVE XDIST
MOV BH,INC_Y ;ASSUME YSTEP = +1
MOV AX,Y2
SUB AX,Y1
JGE DL2 ;IF Y1 <= Y2 THEN NO CHANGE
MOV BH,DEC_Y ;YSTEP = -1
NEG AX ;YDIST = ABS(YDIST)
DL2:
MOV DX,AX ;SAVE YDIST
MOV DI,OFFSET CS:MODIFY_BASE ;POINT TO THE CODE
;TO MODIFY
CMP DX,CX ;DETERMINE LONGEST AXIS
JGE DL3 ;Y IS LONGER, SO SKIP
XCHG CX,DX ;SWAP XDIST, YDIST
XCHG BL,BH ;SWAP INC/DEC X/Y VALUES
DL3: ;MODIFY:
MOV ADJ_LONG_AXIS,BH ;THE 1st INC/DEC CODE
MOV ADJ_MASTER,CX ;MAIN DUTY MASTER ADJUSTMENT
SHR CX,1 ;SET UP CYCLE TESTER
MOV TEST_MASTER,CX ;TEST FOR CYCLING
MOV ALT_ADJ_MASTER,DX ;ALTERNATE ADJUSTMENT
MOV ADJ_SHRT_AXIS,BL ;ALTERNATE INC/DEC CODE
MOV DI,DX ;DI IS COUNTER: LONG AXIS LENGTH
CMP LEN,0 ;IF LENGTH ARG > 0
JE DL4
MOV DI,LEN ;THEN USE IT AS COUNTER
DL4:
MOV BP,SKIP ;GET SKIP COUNT
MOV CX,X1 ; AND OTHER ARGS
MOV DX,Y1
MOV AL,COLOR
XOR BX,BX ;DUTY MASTER STARTS = 0
;--------TOP OF VECTOR PLOTTING LOOP--------------------
DL5:
CMP BP,0 ;TEST SKIP COUNT
JE OK_PLOT
DEC BP
JMP SHORT NO_PLOT
OK_PLOT:
CALL PLOTDOT ;PLOT A DOT
;
;MOST OF THE FOLLOWING CODE IS MODIFIED BY THE PREVIOUS SEQUENCE.
;THE 1111H'S ARE DUMMY VALUES THAT ARE ALWAYS OVERLAYED.
;
MODIFY_BASE LABEL BYTE
NO_PLOT:
INC CX ;INC/DEC CX/DX: ADJUST LONG AXIS PTR
ADD BX,1111H ;XDIST OR YDIST: ADJUST DUTY MASTER
CMP BX,1111H ;YDIST OR XDIST: CHECK CYCLE POSITION
JLE DL6 ;SKIP IF SHORT AXIS IS STILL OK
SUB BX,1111H ;XDIST OR YDIST: ADJUST DUTY MASTER
INC DX ;INC/DEC DX/CX: ADJUST SHORT AXIS PTR
DL6:
DEC DI ;DI IS USED AS COUNTER
JGE DL5 ;DO NEXT DOT IF NOT FINISHED
;--------------------------------------------------
RET ;FAR RETURN BACK TO CALLER
DRAWLINE ENDP
;this routine plots the pixel at column CX (0-319) or (0-639)
; row DX (0-199)
; color AL (0-3) or (0-1) in high res
;note: a much faster routine
; can be wiritten to plot dots
;
PLOTDOT PROC NEAR
PUSH AX
PUSH DI ;BIOS DESTROYS THESE REGISTERS
PUSH BP
MOV AH,12 ;WRITE_DOT FUNCTION
INT 10H ; VIDEO I/O CALL
POP BP
POP DI
POP AX
RET ;NEAR RETURN TO DRAWLINE PROC
PLOTDOT ENDP
CSEG ENDS