| ------------------------------------------------------------------------------
| vwputs.s -- output a character string to a 2-bit per pixel graphics window
| Version 9 -- 1987-07-28 -- D.N. Lynx Crowe
| (c) Copyright 1987 -- D.N. Lynx Crowe
| ------------------------------------------------------------------------------

|	vwputs(obase, nw, fg, bg, row, col, str)
|	int *obase, nw, fg, bg, row, col;
|	char *str;

|		Outputs characters from the string at 'str' to an 'nw'
|		character wide 2-bit per pixel graphics window at 'obase'
|		at ('row','col'), using 'fg' as the foreground color, and
|		'bg' as the background color.  Uses cgtable[][256] as the
|		VSDD formatted character generator table.
|		No error checks are done.
| ------------------------------------------------------------------------------

		.text
		.xdef	_vwputs

		.xref	_cgtable

| Argument offsets from a6:

OBASE		=	8		| L:  Output area base address
NW		=	12		| W:  Character width of output area
FG		=	14		| W:  Foreground color
BG		=	16		| W:  Background color
ROW		=	18		| W:  Row
COL		=	20		| W:  Column
STR		=	22		| L:  String base address

| Miscellaneous constants:

HPIX		=	8		| Horizontal pixels in the character

NVPIX		=	12		| Vertical pixels in the character
VPITCH		=	12		| Vertical pitch between characters

| Register usage:

|	d0	output word and scratch
|	d1	CG word and scratch
|	d2	pixel counter
|	d3	foreground color (in the 2 ms bits)
|	d4	background color (in the 2 ms bits)
|	d5	width of the area in bytes
|	d6	scan line counter

|	a0	CG table pointer
|	a1	output area scan line pointer
|	a2	input character pointer
|	a3	output area character pointer

		.page

_vwputs:	link	a6,#0		| Link stack frames
		movem.l	d3-d6/a3,-(a7)	| Save registers we use
		move.w	#14,d1		| Set shift constant
		move.w	FG(a6),d3	| Setup foreground color
		lsl.w	d1,d3		| ... in ms 2 bits of d3
		move.w	BG(a6),d4	| Setup background color
		lsl.w	d1,d4		| ... in ms 2 bits of d4
		move.w	NW(a6),d5	| Get width in characters in d5
		lsl.w	#1,d5		| ... make it words
		move.w	ROW(a6),d0	| Calculate output address
		move.w	#VPITCH,d1	| ...
		mulu	d1,d0		| ... ROW * VPITCH
		add.w	#NVPIX-1,d0	| ... + NVPIX-1
		mulu	d5,d0		| ... * NW
		clr.l	d1		| ...
		move.w	COL(a6),d1	| ... + (COL * 2)
		lsl.l	#1,d1		| ...
		add.l	d1,d0		| ...
		add.l	OBASE(a6),d0	| ... + OBASE
		movea.l	d0,a3		| Leave output address in a3
		movea.l	STR(a6),a2	| Put string address in a2

		.page
cgl0:		clr.l	d0		| Clear out upper bits of d0
		move.b	(a2)+,d0	| Get next character
		beq	cgl5		| Done if character EQ 0

		movea.l	a3,a1		| Establish output pointer in a1
		adda.l	#2,a3		| Update output pointer for next char.
		lea	_cgtable,a0	| Establish CG pointer in a0
		lsl.w	#1,d0		| ... 2 * character
		adda.w	d0,a0		| ... + _cgtable address
		move.w	#NVPIX-1,d6	| Set scan line counter in d6

cgl1:		move.w	#HPIX-1,d2	| Set pixel counter in d2
		move.w	(a0),d1		| Get character generator word in d1

cgl2:		lsr.w	#2,d0		| Shift output word right 1 pixel
		btst.l	#0,d1		| Check CG word ls bit
		beq	cgl3		| Set background color if bit EQ 0

		or.w	d3,d0		| OR foreground color into output word
		bra	cgl4		| Go update CG word

cgl3:		or.w	d4,d0		| OR background color into  output word

cgl4:		lsr.w	#1,d1		| Shift CG word right 1 pixel
		dbf	d2,cgl2		| Loop for all 8 pixels

		move.w	d0,(a1)		| Store output word in output bitmap
		suba.w	d5,a1		| Update output pointer
		adda.l	#512,a0		| Update CG pointer for next scan line
		dbf	d6,cgl1		| Loop for all scan lines

		bra	cgl0		| Loop for next character

cgl5:		movem.l	(a7)+,d3-d6/a3	| Restore registers
		unlk	a6		| Unlink stack frames
		rts			| Return to caller

		.end