;===========
; CONSTANTS
;===========

NUMSTARS	EQU	16



;	Plan:
;		Ship at rest		0 - 4
;		Flash			5
;		Ship at warp		25
;		Crazy background
;		Ship moves off
;		Back to stars
;		Rasterbars+credits
;		Done

	;=====================
	;=====================
	;=====================
	; Starfield Demo
	;=====================
	;=====================
	;=====================

starfield_demo:

	;================================
	; Clear screen and setup graphics
	;================================

	jsr	clear_screens_notext	 ; clear top/bottom of page 0/1
	jsr     set_gr_page0
	bit	FULLGR

	;===============
	; Init Variables
	;===============
	lda	#0							; 2
	sta	DRAW_PAGE						; 3
	sta	RANDOM_POINTER						; 3
	; always multiply with low byte as zero
	sta	NUM2L							; 3
	sta	FRAME_COUNT

	ldy	#(NUMSTARS-1)						; 2
init_stars:
	jsr	random_star						; 6
	dey								; 2
	bpl	init_stars						; 2nt/3

	;===========================
	;===========================
	; Main Loop
	;===========================
	;===========================

starfield_loop:

	;===============
	; clear screen
	;===============
	jsr	clear_all						; 6+
									; 6047

	;===============
	; draw the stars
	;===============
	jsr	draw_stars

	;================
	; draw the ship
	;================

	lda	#>ship_forward
	sta	INH
	lda	#<ship_forward
	sta	INL

	lda	#15
	sta	XPOS
	lda	#30
	sta	YPOS
	jsr	put_sprite


	;==================
	; flip pages
	;==================

	jsr	page_flip						; 6

	inc	FRAME_COUNT
	lda	FRAME_COUNT
	cmp	#$ff
	beq	done_stars

	;==================
	; loop
	;==================

	jmp	starfield_loop						; 3
done_stars:
	rts



	;=====================
	;=====================
	;=====================
	; Starfield Credits
	;=====================
	;=====================
	;=====================
starfield_credits:

	;================================
	; Clear screen and setup graphics
	;================================

	jsr	clear_screens		; clear top/bottom of page 0/1
	jsr     set_gr_page0

	lda	#0							; 2
	sta	DRAW_PAGE
	jsr	credits_draw_text_background
	lda	#4							; 2
	sta	DRAW_PAGE
	jsr	credits_draw_text_background

	;===============
	; Init Variables
	;===============
	lda	#0							; 2
	sta	DRAW_PAGE						; 3
	sta	RANDOM_POINTER						; 3
	sta	SCREEN_Y
	; always multiply with low byte as zero
	sta	NUM2L							; 3
	sta	FRAME_COUNT
	sta	YY		; which credit
	sta	LOOP		; delay loop

	lda	#>credits	; load credits pointer
	sta	OUTH
	lda	#<credits
	sta	OUTL

	; Initialize stars

	ldy	#(NUMSTARS-1)						; 2
init_stars2:
	jsr	random_star						; 6
	dey								; 2
	bpl	init_stars2						; 2nt/3

	; Initialize the credits

	jsr	init_credits

	;===========================
	;===========================
	; StarCredits Loop
	;===========================
	;===========================

starcredits_loop:

	;===============
	; clear screen
	;===============
	jsr	clear_top						; 6+


	;===============
	; draw the stars
	;===============
	jsr	draw_stars

	;====================
	; draw the rasterbars
	;====================

	jsr	draw_rasters

	;====================
	; draw the credits
	;====================

	jsr	draw_credits
	jsr	credits_draw_bottom

	;==================
	; flip pages
	;==================

	jsr	page_flip						; 6

	inc	FRAME_COUNT

	lda	YY
	cmp	#15				; NUMBER OF CREDITS
	beq	done_star_credits

	;==================
	; loop
	;==================

	jmp	starcredits_loop						; 3
done_star_credits:
	rts




	;======================================================
	;======================================================
	; draw stars
	;======================================================
	;======================================================
	; draws stars

draw_stars:
	; start at 15 and count down (rather than 0 and count up)
	ldx	#(NUMSTARS-1)						; 2

draw_stars_loop:
	stx	XX							; 3

	;================
	; calculate color
	;================

	lda	#$ff		; want if z<16, color = 5		; 2
	sta	COLOR		; 	if 16<z<32 color = 13		; 3
				;	if 32<z<64 color = 15

	lda	star_z,X						; 4
	tay			; put star_z[i] in X for later		; 2

	cmp	#32							; 2
	bpl	done_color						; 2nt/3

	cmp	#16		; 15 -1 16 0 17 1			; 2
	bpl	second_color						; 2nt/3

	lda	#$55							; 2
	sta	COLOR							; 3

	jmp	done_color						; 3
second_color:
	lda	#$dd							; 2
	sta	COLOR							; 3

done_color:


	; calculate x value, stars[i].x/stars[i].z

	; put 1/stars[i].z in NUM1H:NUM1L and multiply

	lda	z_table,Y						; 4
	sta	NUM1L		; F					; 3

	; adjust spacez for 58+
	; all this logic to avoid having a 128 byte table of mostly zero

	lda	#0		; I					; 2
	clc								; 2
	cpy	#60		; 59 -1 60 0 61 1			; 2
	bmi	no_adjust						; 2nt/3
	adc	#1		; 60, 61 = 1				; 2
	cpy	#62		; 61 -1 62 0 63 1			; 2
	bmi	no_adjust						; 2nt/3
	adc	#1		; 62 = 2				; 2
	cpy	#63		; 62 = -1 63 = 0 64 = not possible	; 2
	bne	no_adjust						; 2nt/3
	adc	#2		; 63 = 4				; 2
no_adjust:
	sta	NUM1H		; store int part of spacez		; 3

	; load stars[i].x into NUM2H:NUM2L
	; NUM2L is always zero
	ldy	XX							; 3

	lda	star_x,Y						; 4
	sta	NUM2H							; 3


	sec			; don't reuse old values		; 2
	jsr	multiply						; 6+?

	; integer result in X
	txa								; 2
	clc								; 2
	adc	#20		; center on screen			; 2

	sta	XPOS		; save for later			; 3

	; calculate y value, stars[i].y/stars[i].z

	; 1/stars[i].z is still in NUM1H:NUM1L

	ldy	XX		; reload index				; 3

	lda	star_y,Y	; load integer part of star_		; 4
	sta	NUM2H							; 3
	clc			; reuse old values			; 2
	jsr	multiply						; 6+

	; integer result in X
	txa								; 2
	clc								; 2
	adc	#20		; center the value			; 2

	tay			; Y is YPOS				; 2
	sty	YPOS		; put Y value in Y to plot		; 3


	;============================
	; Check Limits
	;============================

	bmi	new_star						; 2nt/3
y_limit_smc:
	cpy	#40							; 2
	bpl	new_star		; if < 0 or > 40 then done	; 2nt/3

	lda	XPOS							; 3
	bmi	new_star						; 2nt/3
	cmp	#40							; 2
	bpl	new_star		; if < 0 or > 40 then done	; 2nt/3

	; FIXME: sort out all of these jumps to be more efficient
	bmi	plot_star						; 2

new_star:
	ldy	XX							; 3
	jsr	random_star						; 6

	jmp	plot_star_continue					; 3

plot_star:
	jsr	plot							; 6

plot_star_continue:

	;==============================
	ldx	XX							; 3

	dex								; 2
	bmi	move_stars						; 2nt/3
	bpl	draw_stars_loop						; 2nt/3

	;=============================
	; Move stars
move_stars:
	ldy	#(NUMSTARS-1)						; 2
move_stars_loop:
				; increment z
	clc			; if z >= 64 new star			; 2
	lda	star_z,Y						; 4
	adc	#1							; 2
	sta	star_z,Y						; 4
	and	#64							; 2
	beq	move_loop_skip						; 2nt/3

	jsr	random_star	; new random star			; 6

move_loop_skip:
	dey								; 2
	bpl	move_stars_loop						; 2nt/3

	rts


	;==================================================
	;==================================================
	; Random Star
	;==================================================
	;==================================================
	; star number in Y
	; FIXME: increment at end?
	; X trashed
random_star:
	; random x location
	ldx	RANDOM_POINTER						; 3

	lda	random_table,X						; 4
	sta	star_x,Y						; 5
	inx								; 2

	; random y location
	lda	random_table,X						; 4
	sta	star_y,Y						; 5
	inx								; 2

	; random z location
	lda	random_table,X						; 4
	and	#$3f							; 2
	sta	star_z,Y						; 5
	inx								; 2

	stx	RANDOM_POINTER						; 3

	rts								; 6

;======================
; some "random" numbers
;======================
random_table:
	.byte	103,198,105,115, 81,255, 74,236, 41,205,186,171,242,251,227, 70
	.byte	124,194, 84,248, 27,232,231,141,118, 90, 46 ,99, 51,159,201,154
	.byte	102, 50, 13,183, 49, 88,163, 90, 37, 93,  5, 23, 88,233, 94,212
	.byte	171,178,205,198,155,180, 84, 17, 14,130,116, 65, 33, 61,220,135
	.byte	112,233, 62,161, 65,225,252,103, 62,  1,126,151,234,220,107,150
	.byte	143, 56, 92, 42,236,176, 59,251, 50,175, 60, 84,236, 24,219, 92
	.byte     2, 26,254, 67,251,250,170, 58,251, 41,209,230,  5, 60,124,148
	.byte	117,216,190, 97,137,249, 92,187,168,153, 15,149,177,235,241,179
	.byte	  5,239,247,  0,233,161, 58,229,202, 11,203,208, 72, 71,100,189
	.byte	 31, 35, 30,168, 28,123,100,197, 20,115, 90,197, 94, 75,121, 99
	.byte	 59,112,100, 36, 17,158,  9,220,170,212,172,242, 27, 16,175, 59
	.byte	 51,205,227, 80, 72, 71, 21, 92,187,111, 34, 25,186,155,125,245
	.byte	 11,225, 26, 28,127, 35,248, 41,248,164, 27, 19,181,202, 78,232
	.byte	152, 50, 56,224,121, 77, 61, 52,188, 95, 78,119,250,203,108,  5
	.byte	172,134, 33, 43,170, 26, 85,162,190,112,181,115, 59,  4, 92,211
	.byte	 54,148,179,175,226,240,228,158, 79, 50, 21, 73,253,130, 78,169

z_table:
	; 1/16.0 - 1/12.25
	.byte	$10,$10,$10,$10,$11,$11,$11,$11,$12,$12,$12,$13,$13,$14,$14,$14
	; 1/12.0 - 1/8.25
	.byte	$15,$15,$16,$16,$17,$17,$18,$18,$19,$1A,$1A,$1B,$1C,$1D,$1E,$1F
	; 1/8.0 - 1/4.25
	.byte	$20,$21,$22,$23,$24,$25,$27,$28,$2A,$2C,$2E,$30,$33,$35,$38,$3C
	; 1/4.0 - 1/0.25
	.byte	$40,$44,$49,$4E,$55,$5D,$66,$71,$80,$92,$AA,$CC,$00,$55,$00,$00