TITLE	"MP4 by Douglas Jones"
;	program to print a fractal pattern
;	output should be centered on the screen
	USE	"hawk.h"
	USE	"monitor.h"

; use of this array eliminates the need to
; compute the dimensions on the fly.
; in general, ROWS[i] = 2*ROWS[i-1] + ROWS[i-2]

; array of height versus  order
ROWS:   W	0	; 0
        W	1	; 1
        W	2	; 2
        W	5	; 3
        W	12	; 4
        W	29	; 5
        W	70	; 6
        W	169	; 7
        W	408	; 8
        W	985	; 9

	SUBTITLE "PLOT: The recursive fractal plotter"
; activation record for PLOT,
;retad	=	0
R8SV	=	4
R9SV	=	8
R10SV	=	12
R11SV	=	16
R12SV	=	20
ARSIZE	=	24

PLOT:   ; expects R3 = order of figure
	; expects R4 = x coordinate of upper left of figure
	; expects R5 = y     "      "    "    "   "    "
	STORES	R1,R2
	ADDSI	R3,-1		; order = order - 1;
	BLT	PLOTQT		; if (order >= 0) {
	BGT	PLOTEL		;   if (order = 0) { -- basis case

	ADDI	R2,R2,ARSIZE
	MOVE	R3,R4
	MOVE	R4,R5
	LIL	R1,PUTAT
	JSRS	R1,R1		;     putat(x,y)
	LIS	R3,'['
	LIL	R1,PUTCHAR
	JSRS	R1,R1		;     putchar('[')
	LIS	R3,']'
	LIL	R1,PUTCHAR
	JSRS	R1,R1		;     putchar(']')
	ADDI	R2,R2,-ARSIZE

	BR	PLOTQT
PLOTEL:				;   } else { -- order > 0, fun case
	STORE	R8,R2,R8SV
	STORE	R9,R2,R9SV
	STORE	R10,R2,R10SV
	STORE	R11,R2,R11SV
	STORE	R12,R2,R12SV

	MOVE	R8,R3		;     -- order in R8
	MOVE	R9,R4		;     -- X in R9
	MOVE	R10,R5		;     -- Y in R10
	LEA	R12,ROWS
	MOVESL  R11,R8,2
	ADD	R12,R11,R12
	LOADS	R11,R12		;     big = ROWS[order] -- in R11
	ADDSI	R12,-4
	LOADS	R12,R12		;     lit = ROWS[order-1] -- in R12

	ADDI	R2,R2,ARSIZE
				;     -- upper left
	JSR	R1,PLOT		;     plot(order,x,y)

				;     -- lower left
	MOVE	R3,R8
	MOVE	R4,R9
	ADD	R5,R11,R12
	ADD	R5,R5,R10
	JSR	R1,PLOT		;     plot(order,x,big+lit+y)

				;     -- upper right
	MOVE	R3,R8
	ADD	R4,R11,R12
	ADDSL   R4,R9,1
	MOVE	R5,R10
	JSR	R1,PLOT		;     plot(order,(big+lit)*2+x,y)
	
				;     -- lower right
	MOVE	R3,R8
	ADD	R4,R11,R12
	ADDSL   R4,R9,1
	ADD	R5,R11,R12
	ADD	R5,R5,R10
	JSR	R1,PLOT		;     plot(order,(big+lit)*2+x,big+lit+y)
	
				;     -- middle
	MOVE	R3,R8
	ADDSI	R3,-1
	MOVE	R4,R11
	ADDSL   R4,R9,1
	ADD	R5,R11,R10
	JSR	R1,PLOT		;     plot(order-1,(big)*2+x,big+y)
	
	ADDI	R2,R2,-ARSIZE

	LOAD	R8,R2,R8SV
	LOAD	R9,R2,R9SV
	LOAD	R10,R2,R10SV
	LOAD	R11,R2,R11SV
	LOAD	R12,R2,R12SV
PLOTQT:				; } }
	LOADS	R1,R2
	JUMPS	R1		; return

	SUBTITLE "main program"
	S	MAIN
	INT	MAIN

	SUBTITLE "MAIN: position the fractal on screen"
; activation record for MAIN
;retad	=	0
ARSIZE	=	4
MAIN:   ; expects R3 = w -- screen width
	; expects R4 = h -- screen height
	STORES	R1,R2

				; -- find d, the limiting screen dimension
	MOVE	R5,R3
	SR	R5,1		; d = w/2 -- in R5

	CMP	R4,R5
	BGE	MAGOTD		; if (h < d)
	MOVE	R5,R4		;   d = h;
MAGOTD:				; }

				; -- find order, limited by d
	LEA	R6,ROWS
	LIS	R7,0		; order = 0
MAGETO:				; loop {
	LOADS	R8,R6
	CMP	R8,R5
	BGT	MAGOTO		;   if (ROWS[order] > d) break;

	ADDSI	R7,1		;   order = order + 1
	ADDSI	R6,4

	BR	MAGETO		; }
MAGOTO:
	ADDSI	R7,-1		; order = order - 1
	ADDSI	R6,-4		; -- above loop overshoots by one

	LOADS	R6,R6		; r = ROWS[order] -- in R6

				; -- compute midpoint of screen
	SR	R3,1		; x = width/2
	SR	R4,1		; y = height/2

				; -- compute upper left corner of figure
	SUB	R3,R3,R6	; x = x - rows
	SR	R6,1
	SUB	R4,R4,R6	; y = y - rows/2

				; -- plot the figure
	MOVE	R5,R4	
	MOVE	R4,R3	
	MOVE	R3,R7
	ADDI	R2,R2,ARSIZE
	JSR	R1,PLOT		; plot(order,x,y)
	ADDI	R2,R2,-ARSIZE

	
	LOADS	R1,R2
	JUMPS	R1		; return