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CGAGRAFA.ASM
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Assembly Source File
|
1987-08-31
|
3KB
|
183 lines
;
; grafix --- cgagrafa.asm
;
; stuff to plot points fast in 8086 assembler (BLEECH!!!)
;
; Written 4/87 by Scott Snyder (ssnyder@romeo.caltech.edu or @citromeo.bitnet)
;
; Modified 5/29/87 by sss to allow for different memory models
;
title cgagrafa
include macros.ah
df CGA_point
df CGA_write_pix
sseg
endss
g_oddoff equ 02000h
g_linsiz equ 80
dseg
ex g_drawbuf, dword
ex g_pixbyte, word
ex g_bitpix, word
ex g_colormask, byte
ex g_cmask_tbl, byte
ex g_hicolormask, byte
ex g_xor, word
ex g_xcliplo, word
ex g_xcliphi, word
ex g_ycliplo, word
ex g_ycliphi, word
endds
cseg _cgagrafa
; plot a point. ax = y; bl = c; cx = x;
pBegin plot
les si, g_drawbuf ; get address of buffer
sar ax, 1 ; y /= 2
jnc p1 ; add in offset if it was odd
add si, g_oddoff
p1: mov dx, g_linsiz ; y * g_linsiz
mul dx
add si, ax ; add to offset
mov ax, cx ; x to AC (ohhh... what symmetry!)
mov dx, 0
div g_pixbyte
add si, ax ; add quotient to offset (now complete)
and bl, g_colormask ; get cmask
mov bl, g_cmask_tbl[bx]
mov cx, g_bitpix ; only works for bitpix = 0 or 1!
dec cx
shl dx, cl ; dx = mask shift count
mov cx, dx
mov dl, g_hicolormask ; get mask
shr dl, cl ; shift it
and bx, dx ; bx = cmask & mask
mov al, es:[si] ; get image byte
cmp g_xor, 0 ; xor mode?
jne p2
not dl ; no - (*ptr & ~mask) | (cmask & mask)
and al, dl
or al, bl
jmp p3
p2: xor al, bl ; yes - *ptr ^ (cmask & mask)
p3: mov es:[si], al ; done!
ret
pEnd plot
;
; C interface for point plotter
;
; CGA_point(x, y, c)
;
pBegin CGA_point
push bp
mov bp, sp
push si
push di
mov ax, [bp+argbase+2]
mov bx, [bp+argbase+4]
mov cx, [bp+argbase]
call plot
pop di
pop si
mov sp, bp
pop bp
ret
pEnd CGA_point
;
; write for pixels for circle drawing
;
; void CGA_write_pix(x1, y1, x2, y2, c)
;
pBegin CGA_write_pix
push bp
mov bp, sp
push si
push di
mov bx, [bp+argbase+8] ; bx = c (for plot)
mov cx, [bp+argbase] ; cx = x1
cmp cx, g_xcliplo ; check for clipping
jb w2
cmp cx, g_xcliphi
ja w2
mov ax, [bp+argbase+2] ; ax = y1
cmp ax, g_ycliplo ; do clipping
jb w1
cmp ax, g_ycliphi
ja w1
push bx ; plot (x1, y1)
push cx
call plot
pop cx
pop bx
w1: mov ax, [bp+argbase+6] ; ax = y2
cmp ax, g_ycliplo
jb w2
cmp ax, g_ycliphi
ja w2
push bx ; plot (x1, y2)
call plot
pop bx
w2: mov cx, [bp+argbase+4] ; cx = x2
cmp cx, g_xcliplo
jb w4
cmp cx, g_xcliphi
ja w4
mov ax, [bp+argbase+2] ; ax = y1
cmp ax, g_ycliplo ; do clipping
jb w3
cmp ax, g_ycliphi
ja w3
push bx ; plot (x2, y1)
push cx
call plot
pop cx
pop bx
w3: mov ax, [bp+argbase+6] ; ax = y2
cmp ax, g_ycliplo
jb w4
cmp ax, g_ycliphi
ja w4
call plot ; plot (x2, y2)
w4: pop di
pop si
mov sp, bp
pop bp
ret
pEnd CGA_write_pix
endcs _cgagrafa
end