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C/C++ Users Group Library 1996 July
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C-C++ Users Group Library July 1996.iso
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vol_200
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255_01
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gpline.asm
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Assembly Source File
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1988-03-28
|
10KB
|
434 lines
page 80,132
page
;
; Kent Cedola
; 2015 Meadow Lake Court
; Norfolk, Virginia 23518
;
dgroup group _data
_data segment word public 'data'
assume ds:dgroup
extrn _gdcolor:byte,_gdmerge:byte
extrn _gdcur_x:word,_gdcur_y:word
extrn _gdvw_x1:word,_gdvw_x2:word,_gdvw_x3:word
extrn _gdvw_y1:word,_gdvw_y2:word,_gdvw_y3:word
extrn _gdc_flg:byte,_gds_flg:byte
extrn _gdstyle:dword,_gdgseg:word
_data ends
_text segment byte public 'code'
assume cs:_text,ds:dgroup
public _gpline
_gpline proc near
push bp
mov bp,sp
push si
push di
mov cx,_gdcur_x ; Load starting X coordinate (X1)
mov bx,_gdcur_y ; Load starting Y coordinate (Y1)
mov si,[bp+4] ; Load ending X coordinate (X2)
mov di,[bp+6] ; Load ending Y coordinate (Y2)
mov _gdcur_x,si ; Store new current (X,Y) coordinates
mov _gdcur_y,di ; ...
mov _gdc_flg,0 ; Set the clipping flag to zero
; Perform the Cohen-Sutherland two-step clipping algorithm, in which a
; four-element code indicates the position of a point. From pages 36-37 of
; the book "Microcomputer Displays, Graphics, and Animation" by Bruce Atwick.
dline01:
XOR AX,AX
; Generate 4-element start and end point codes
CMP BX,_gdvw_y1
JGE $+5
OR AH,8
CMP BX,_gdvw_y2
JLE $+5
OR AH,4
CMP CX,_gdvw_x1
JGE $+5
OR AH,2
CMP CX,_gdvw_x2
JLE $+5
OR AH,1
CMP DI,_gdvw_y1
JGE $+4
OR AL,8
CMP DI,_gdvw_y2
JLE $+4
OR AL,4
CMP SI,_gdvw_x1
JGE $+4
OR AL,2
CMP SI,_gdvw_x2
JLE $+4
OR AL,1
OR AX,AX
JNZ dline15
JMP dline09
dline15:
mov _gdc_flg,1
TEST AH,AL
JZ dline02
mov _gdc_flg,2
jmp theend
dline02:
OR AL,AL
JNZ dline03
; Swap start and end points
XCHG CX,SI ;
XCHG BX,DI ;
XCHG AH,AL
dline03:
TEST AL,2
JNZ dline06
TEST AL,4
JNZ dline07
TEST AL,8
JNZ dline08
dline05:
MOV BP,DI
SUB BP,BX
MOV AX,_gdvw_x2
SUB AX,CX
IMUL BP
MOV BP,SI
SUB BP,CX
IDIV BP
ADD AX,BX
MOV SI,_gdvw_x2
MOV DI,AX
JMP dline01
dline06:
MOV BP,DI
SUB BP,BX
MOV AX,_gdvw_x1
SUB AX,CX
IMUL BP
MOV BP,SI
SUB BP,CX
IDIV BP
ADD AX,BX
MOV SI,_gdvw_x1
MOV DI,AX
JMP dline01
dline07:
MOV BP,SI
SUB BP,CX
MOV AX,_gdvw_y2
SUB AX,BX
IMUL BP
MOV BP,DI
SUB BP,BX
IDIV BP
ADD AX,CX
MOV SI,AX
MOV DI,_gdvw_y2
JMP dline01
dline08:
MOV BP,SI
SUB BP,CX
MOV AX,_gdvw_y1
SUB AX,BX
IMUL BP
MOV BP,DI
SUB BP,BX
IDIV BP
ADD AX,CX
MOV SI,AX
MOV DI,_gdvw_y1
JMP dline01
dline09:
mov dx,03CEh ; Load address of EGA graphic controller
mov ah,_gdmerge ; Load current merge setting
mov al,03h ; Load address of merge register
out dx,ax ; Set the graphic controller function
mov ax,00205h ; Load parameters for write mode #2
out dx,ax ; Set the graphic controller write mode
mov dx,si
cmp dx,cx ; Is X2 >= X1?
jae noxchg ; Yes, continue
xchg cx,dx ; No, then switch (X1,Y1) with (X2,Y2)
xchg bx,di ; ...
noxchg:
sub dx,cx ; Compute Delta X := X2 - X1;
sub di,bx ; Compute Delta Y := Y2 - Y1;
mov si,bx ; Compute SI = Y * 80 for row offset
shl si,1 ; ... (SI = Y * 2)
shl si,1 ; ... (SI = Y * 4)
add si,bx ; ... (SI = Y * 5)
shl si,1 ; ... (SI = Y * 10)
shl si,1 ; ... (SI = Y * 20)
shl si,1 ; ... (SI = Y * 40)
shl si,1 ; ... (SI = Y * 80)
mov bx,cx ; Compute BX = X / 8 for column offset
shr bx,1 ; ... (BX = X / 2)
shr bx,1 ; ... (BX = X / 4)
shr bx,1 ; ... (BX = X / 8)
add bx,si ; Compute BX = BX + SI, first byte
mov si,dx ; SI now contains delta X
mov dx,03CEh ;
mov al,8 ;
out dx,al ;
inc dx ;
and cl,7 ; Compute AL = starting bit mask
mov al,080h ; ... load default of bit 0
ror al,cl ; ... rotate to the starting bit mask
cmp _gds_flg,0 ; Do we use the current line style?
jne style
jmp line
style:
push si
les si,_gdstyle
cmp byte ptr es:[si],1
jne style00
mov ah,es:[si+1]
pop si
jmp line
style00:
pop si
mov [bp+4],si
mov [bp+6],di
or di,di
jns style02
neg di
cmp di,si
ja style01
jmp octant8
style01:
jmp octant7
style02:
cmp di,si
ja octant2
octant1:
mov cx,si ; Count Down = DX
mov di,si ; Error Register = -DX/2
shr di,1 ; ...
neg di ; ...
les si,_gdstyle
mov ah,es:[si]
inc si
octant1L:
call putdot
ror al,1 ; Compute X := X + 1;
adc bx,0 ; ...
add di,[bp+6] ;
jle octant1L ;
add bx,80 ; Compute Y := Y + 1;
sub di,[bp+4] ;
jmp short octant1L ;
octant2:
mov cx,di ; Count Down = DY
shr di,1 ; Error Register = -DX/2
neg di ; ...
les si,_gdstyle
mov ah,es:[si]
inc si
octant2L:
call putdot
add bx,80 ; Compute Y := Y + 1;
add di,[bp+4] ;
jle octant2L ;
ror al,1 ; Compute X := X + 1;
adc bx,0 ; ...
sub di,[bp+6] ;
jmp short octant2L ;
octant7:
mov cx,di ; Count Down = DY
shr di,1 ; Error Register = -DY/2
neg di ; ...
les si,_gdstyle
mov ah,es:[si]
inc si
octant7L:
call putdot
sub bx,80 ; Compute Y := Y + 1;
add di,[bp+4] ;
jle octant7L ;
ror al,1 ; Compute X := X + 1;
adc bx,0 ; ...
add di,[bp+6] ;
jmp short octant7L ;
octant8:
mov cx,si ; Count Down = DX
mov di,si ; Error Register = -DX/2
shr di,1 ; ...
neg di ; ...
les si,_gdstyle
mov ah,es:[si]
inc si
octant8L:
call putdot
ror al,1 ; Compute X := X + 1;
adc bx,0 ; ...
sub di,[bp+6] ;
jle octant8L ;
sub bx,80 ; Compute Y := Y + 1;
sub di,[bp+4] ;
jmp short octant8L ;
line:
mov ah,_gdcolor ; Load current color setting
push bp
mov es,_gdgseg
or di,di
jns line01
neg di
cmp di,si
ja lineoct7
jmp short lineoct8
line01:
cmp di,si
ja lineoct2
lineoct1:
mov cx,si ; Count Down = DX
mov bp,si ; Error Register = -DX/2
shr bp,1 ; ...
neg bp ; ...
lineoct1L:
out dx,al
cmp byte ptr es:[bx],0
mov es:[bx],ah
dec cx
js linedone
ror al,1
adc bx,0
add bp,di
jle lineoct1L
add bx,80
sub bp,si
jmp short lineoct1L
lineoct2:
mov cx,di ; Count Down = DY
mov bp,di ; Error Register = -DY/2
shr bp,1 ; ...
neg bp ; ...
lineoct2L:
out dx,al
cmp byte ptr es:[bx],0
mov es:[bx],ah
dec cx
js linedone
add bx,80
add bp,si
jle lineoct2L
ror al,1
adc bx,0
sub bp,di
jmp short lineoct2L
lineoct7:
mov cx,di ; Count Down = -DY
mov bp,di ; Error Register = DY/2
shr bp,1 ; ...
neg bp ;
lineoct7L:
out dx,al
cmp byte ptr es:[bx],0
mov es:[bx],ah
dec cx
js linedone
sub bx,80
add bp,si
jle lineoct7L
ror al,
