;-------------------------routine begins--------------------------+
; ROUTINE FOR plotting a point on med-res color screen
;
; FUNCTION: This routine plots a point on the medium resolution
; color screen.  The pixel at the specified location is given a
; specified color, overwriting the old color.
; INPUT: Upon entry:
;        x-coordinate (0-319) of the point is in SI
;	 y-coordinate (0-199) of the point is in DI
;	 color (0-3) is in DX
; OUTPUT: Just to the screen
; REGISTERS USED:  No registers modified.  SI,DI,DX are used for
;                  input.
; SEGMENTS REFERENCED:  Upon entry ES: must point to the video RAM
; at B8000h and DS: must point to a data segment containing the fol-
; lowing look-up table of rotated color masks:
;
ctable	dw	0003Fh,0403Fh,0803Fh,0C03Fh
	dw	000CFh,010CFh,020CFh,030CFh
	dw	000F3h,004F3h,008F3h,00CF3h
	dw	000FCh,001FCh,002FCh,003FCh
;
; ROUTINES CALLED:  None
; SPECIAL NOTES: No bounds checking is performed.  The user must
; make sure that the coordinates and the color are in the proper
; ranges.
;
setpt	proc	far
;
	push	bx		; save registers
	push	si
	push	ax
;
; multiply y-coord by bytes per row and adjust for even/odd lines
	mov	ax,di		; get y-coord into low part
	mov	ah,al		;   and into high part.
	and	ax,01FEh	; mask off unwanted parts
	sal	ax,1		; times 41
	sal	ax,1		; times 8
	sal	ax,1		; times 16
	mov 	bx,ax		; goes into adddress
	and	bx,7		; without adjustment
	sal	ax,1		; times 32
	sal	ax,1		; times 64
	add	bx,ax		; adress gets y-coord times 80
;
; compute rotated mask and color
	and	si,3		; adjust pixel position into the index
	sal	si,1		; index times 2
	sal	si,1		; index times 4
	add	si,dx		; 4*pixel position + color
	sal	si,1		; 8*pixel position + 2*color
	mov	ax,ctable[si]	; look up rotated color mask
;
; insert color into the video byte
	and	al,es:[bx]	; get the old byte and remove old pixel
	or	al,ah		; insert new color
	mov	es:[bx],al	; put the byte back
;
	pop	ax		; restore registers
	pop	si
	pop	bx
	ret			; return
;
setpt	endp
;-------------------------routine ends---------------------------+