	TITLE	Hercules Graphics Routines for FRACTINT

;			 required for compatibility if Turbo ASM
IFDEF ??version
	MASM51
	QUIRKS
ENDIF

	.MODEL	medium,c

	.8086
.data

HGCBase 	equ	0B000h		;segment for HGC regen buffer page 0

herc_index	equ	03B4h
herc_cntrl	equ	03B8h
herc_status	equ	03BAh
herc_config	equ	03BFh


; Hercules control/configuration register settings

scrn_on equ	08h
grph	equ	02h
text	equ	20h
enable	equ	03h

.code

;
;
; inithgc -  Initialize the HGC in graphics mode.
;	    Code mostly from the Hercules Graphics Card Owner's Manual.
;
inithgc PROC USES DI SI

	mov	al,enable		; enable mode changes
	mov	dx,herc_config		; same as HGC FULL command
	out	dx,al

	mov	al,grph 		; set graphic mode
	lea	si,gtable		; address of graphic parameters
	mov	bx,0
	mov	cx,4000h
	call	setmd			; call set mode common processing

	ret

inithgc ENDP

;
; termhgc -  Restore the Hercules Graphics Card to text mode.
;	    Code mostly from the Hercules Graphics Card Owner's Manual.
;
termhgc PROC USES DI SI

	mov	al,text 		; set text mode
	lea	si,ttable		; get address of text parameters
	mov	bx,720h
	mov	cx,2000
	call	setmd

	ret

termhgc ENDP

;
; setmd - sets mode to graphic or text depending on al
;	  si = address of parameter table
;	  cx = number of words to be cleared
;	  bx = blank value
;
;	  from Hercules Graphics Card Owner's Manual
;
setmd	PROC NEAR
;
	push	bp
	mov	bp,sp
	push	ax
	push	bx
	push	cx

;    change mode, but without screen on
	mov	dx,herc_cntrl		; get address of control register
	out	dx,al			; al has the mode byte

;    initialize the 6845
	mov	ax,ds
	mov	es,ax			; also point es:si to parameter table

	mov	dx,herc_index		; get index register address
	mov	cx,12			; 12 parameters to be output
	xor	ah,ah			; starting from register 0

parms:	mov	al,ah			; first output register number
	out	dx,al

	inc	dx			; get data register address
	lodsb				; get next byte from param. table
	out	dx,al			; output parameter data

	inc	ah			; increment register number
	dec	dx			; restore index register address
	loop	parms			; go do another one

;    now go clear the buffer
	pop	cx			; get number of words to clear
	mov	ax,HGCBase		; get address off video buffer
	cld				; set auto increment
	mov	es,ax			; set segment for string move
	xor	di,di			; start at offset 0
	pop	ax			; get blank value
	rep	stosw			; repeat store string

;   turn screen on with page 0 active
	mov	dx,herc_cntrl		; get control register address
	pop	ax			; get the mode byte
	add	al,scrn_on		; set the screen-on bit
	out	dx,al

	mov	sp,bp
	pop	bp
	ret

setmd	ENDP
;
; writehgc (x, y, c)  - write a dot at x, y in color color
;  x = x coordinate
;  y = y coordinate
;  color = color
;
writehgc	PROC USES DI SI, x, y, color

	cmp	y,348			; Clip for hardware boundaries
	jge	WtDot030
	cmp	x,720
	jge	WtDot030

	lea	bx,HGCRegen		;set up offset of regen scan line table
	mov	ax,HGCBase		;segment for regen buffer
	mov	es,ax

; calculate byte address of dot in regen buffer
	mov	si,y		;get y coordinate
	shl	si,1		;mult by 2 to get offset in Scan Line Table
	mov	si,[bx][si]	;get address of start of scan line from table
	mov	ax,x		;get x coordinate
	mov	cl,3
	shr	ax,cl		;divide by 8 to get byte offset
	add	si,ax		;es:si has address of byte with the bit
; build the bit mask for the specific dot in the byte
	mov	cx,x		;get x coordinate
	and	cx,0007h	;get bit number within the byte
	mov	al,80h		;prepare bit mask
	shr	al,cl		;al has bit mask
; either turn on the bit or turn it off, depending on the color
	cmp	word ptr color,0	;turn off bit?
	je	WtDot020	;yes -- branch
; turn on the bit
	or	byte ptr es:[si],al
	jmp	short WtDot030
WtDot020:
; turn off the bit
	xor	al,0FFh
	and	byte ptr es:[si],al
WtDot030:
	ret

writehgc	ENDP
;
; readhgc (x,y) - read a dot at x,y
;  x = x coordinate
;  y = y coordinate
;
;  dot value is to be returned in AX
;
readhgc PROC USES DI SI, x,y

	lea	bx,HGCRegen		;set up offset of regen scan line table
	mov	ax,HGCBase		;segment for regen buffer
	mov	es,ax

; calculate byte address of dot in regen buffer
	mov	si,y		;get y coordinate
	shl	si,1		;mult by 2 to get offset in Scan Line Table
	mov	si,[bx][si]	;get address of start of scan line from table
	mov	ax,x		;get x coordinate
	mov	cl,3
	shr	ax,cl		;divide by 8 to get byte offset
	add	si,ax		;es:si has address of byte with the bit

; build the bit mask for the specific dot in the byte
	mov	cx,x		;get x coordinate
	and	cx,0007h	;get bit number within the byte
	mov	al,80h		;prepare bit mask
	shr	al,cl		;al has bit mask

; pick up the bit from the regen buffer
	test	byte ptr es:[si],al
	jz	readhgc020	;branch if bit is zero
	mov	ax,1		;else return foreground bit value
	jmp	short readhgc030
readhgc020:
	xor	ax,ax		;bit is zero
readhgc030:
	ret

readhgc ENDP


.data

gtable	db	35h,2dh,2eh,07h
	db	5bh,02h,57h,57h
	db	02h,03h,00h,00h

ttable	db	61h,50h,52h,0fh
	db	19h,06h,19h,19h
	db	02h,0dh,0bh,0ch

		;offsets into HGC regen buffer for each scan line
HGCRegen	dw	0,8192,16384,24576,90,8282,16474,24666
		dw	180,8372,16564,24756,270,8462,16654,24846
		dw	360,8552,16744,24936,450,8642,16834,25026
		dw	540,8732,16924,25116,630,8822,17014,25206
		dw	720,8912,17104,25296,810,9002,17194,25386
		dw	900,9092,17284,25476,990,9182,17374,25566
		dw	1080,9272,17464,25656,1170,9362,17554,25746
		dw	1260,9452,17644,25836,1350,9542,17734,25926
		dw	1440,9632,17824,26016,1530,9722,17914,26106
		dw	1620,9812,18004,26196,1710,9902,18094,26286
		dw	1800,9992,18184,26376,1890,10082,18274,26466
		dw	1980,10172,18364,26556,2070,10262,18454,26646
		dw	2160,10352,18544,26736,2250,10442,18634,26826
		dw	2340,10532,18724,26916,2430,10622,18814,27006
		dw	2520,10712,18904,27096,2610,10802,18994,27186
		dw	2700,10892,19084,27276,2790,10982,19174,27366
		dw	2880,11072,19264,27456,2970,11162,19354,27546
		dw	3060,11252,19444,27636,3150,11342,19534,27726
		dw	3240,11432,19624,27816,3330,11522,19714,27906
		dw	3420,11612,19804,27996,3510,11702,19894,28086
		dw	3600,11792,19984,28176,3690,11882,20074,28266
		dw	3780,11972,20164,28356,3870,12062,20254,28446
		dw	3960,12152,20344,28536,4050,12242,20434,28626
		dw	4140,12332,20524,28716,4230,12422,20614,28806
		dw	4320,12512,20704,28896,4410,12602,20794,28986
		dw	4500,12692,20884,29076,4590,12782,20974,29166
		dw	4680,12872,21064,29256,4770,12962,21154,29346
		dw	4860,13052,21244,29436,4950,13142,21334,29526
		dw	5040,13232,21424,29616,5130,13322,21514,29706
		dw	5220,13412,21604,29796,5310,13502,21694,29886
		dw	5400,13592,21784,29976,5490,13682,21874,30066
		dw	5580,13772,21964,30156,5670,13862,22054,30246
		dw	5760,13952,22144,30336,5850,14042,22234,30426
		dw	5940,14132,22324,30516,6030,14222,22414,30606
		dw	6120,14312,22504,30696,6210,14402,22594,30786
		dw	6300,14492,22684,30876,6390,14582,22774,30966
		dw	6480,14672,22864,31056,6570,14762,22954,31146
		dw	6660,14852,23044,31236,6750,14942,23134,31326
		dw	6840,15032,23224,31416,6930,15122,23314,31506
		dw	7020,15212,23404,31596,7110,15302,23494,31686
		dw	7200,15392,23584,31776,7290,15482,23674,31866
		dw	7380,15572,23764,31956,7470,15662,23854,32046
		dw	7560,15752,23944,32136,7650,15842,24034,32226
		dw	7740,15932,24124,32316

	END
