Category : Assembly Language Source Code
Archive   : ASM-SUBR.ZIP
Filename : RCHAR

;-------------------------rchar routine begins--------------------------+
; NAME RCHAR
;
; ROUTINE TO PLOT A RASTER CHARACTER
;
; from BLUEBOOK OF ASSEMBLY ROUTINES FOR IBM PC & XT.
; page : 151
;
; FUNCTION: This routine plots a raster character. It uses a raster
; character table in the IBM ROM BIOS. Only ASCII codes 0 - 127 are
; supported/
;
; INPUT: Upon entry:
;
; ACSII code character is in AL
; x-coordinate of upper left corner of character cell is in x0
; y-coordinate of upper left corner of character cell is in y0
; horizontal magnitude is in xmagn
; vertical magnitude is in ymagn
; color of character is in color
;
; OUTPUT: Just to the screen.
;
; REGISTERS USED: No registers are modified.
;
; SEGMENTS REFERENCED: Upon entry ES must point to the video RAM at
; B8000h and DS must point to the data segment used by the box-fill
; routine.
;
; ROUTINES CALLED: SETBOX
;
; SPECIAL NOTES: No bounds checking is performed. Unpredictable results
; will be displayed if the horizontal or vertical magnitude is too large.
; A string of raster characters can be displayed using the GMESSOUT
; routine available on this disk.
;
; ROUTINE TO PLOT A RASTER CHARACTER
;
rchar proc far
;
push si ; save registers
push dx
push cx
push ax
;
; look up pattern for character
;
cbw ; convert from byte to word
sal ax,1 ; times 2
sal ax,1 ; times 4
sal ax,1 ; times 8
add ax,0FA6Eh+7 ; char table plus pattern end
mov si,ax ; here is the offset
;
mov dx,ds ; save old DS
mov ax,0F000h ; point DS to ROM segment
mov ds,ax ; load new data segment
;
; store pattern on the stack
mov cx,8 ; for a count of eight bytes
std ; backward direction
;
rchar1:
lodsb ; load
push ax ; push onto stack
loop rchar1
;
mov ds,dx ; restore orig data segment
;
; get the starting point
mov ax,x0 ; get x-coord
mov x1,ax
mov ax,y0 ; get y-coord
mov y1,ax
;
mov cx,8 ; for a count of 8 rows
;
rchar2:
pop dx ; get the next row
push cx ; save the count
;
mov al,ymagn ; vertical sizing
cbw
dec ax ; one less
add ax,y1 ; add to new dot position
mov y2,ax
;
mov cx,8 ; for a count of 8 dots
;
rchar3:
push cx ; save count
;
mov al,xmagn ; horiz sizing
cbw
dec ax ; one less
add ax,x1 ; add to new dot position
mov x2,ax
;
test al,80h ; check the dot
jz rchar4 ; skip it if zero
call setbox ; plot it if one
;
rchar4:
mov ax,x2 ; next column
inc ax ; one over from end of box
mov x1,ax ; into next dot posn
rol dl,1 ; next dot from pattern
pop cx ; restore dot count
loop rchar3 ; loop for next dot
;
mov ax,x0 ; restore to first column
mov x1,ax ; beginning of row
mov ax,y2 ; next row
inc ax ; one down from end of box
mov y1,ax ; into next row posn
pop cx ; restore row count
loop rchar2 ; loop for next row
;
pop ax ; restore registers
pop cx
pop dx
pop si
;
ret ; return
rchar endp
;-------------------------rchar routine ends---------------------------+