hgr: plasma: forgot a file

graphics/hgr/plasma/twist.s

@@ -0,0 +1,136 @@
+; Ovals
+
+; zero page
+GBASL	= $26
+GBASH	= $27
+YY	= $69
+ROW_SUM = $70
+
+HGR_X           = $E0
+HGR_XH          = $E1
+HGR_Y           = $E2
+HGR_COLOR       = $E4
+HGR_PAGE        = $E6
+
+FRAME	= $FC
+SUM	= $FD
+SAVEX	= $FE
+SAVEY	= $FF
+
+; soft-switches
+FULLGR	= $C052
+PAGE1	= $C054
+
+; ROM routines
+
+HGR2	= $F3D8
+HPOSN	= $F411		; (Y,X),(A)  (values stores in HGRX,XH,Y)
+
+	;================================
+	; Clear screen and setup graphics
+	;================================
+oval:
+
+	jsr	HGR2		; set hi-res 140x192, page2, fullscreen
+
+draw_oval:
+	inc	FRAME
+
+	ldx	#191		; YY
+	stx	HGR_Y
+
+create_yloop:
+	lda	HGR_Y
+	ldx	#39
+	ldy	#0
+
+	jsr	HPOSN		; (Y,X),(A)  (values stores in HGRX,XH,Y)
+
+	; restore values
+
+	ldy	#39		; XX
+
+	lda	FRAME
+	sta	SUM
+
+	lda	HGR_Y		; YY
+	jsr	calcsine_div2
+
+	ldx	HGR_Y		; YY
+
+	sta	ROW_SUM
+create_xloop:
+
+	tya			; XX
+	jsr	calcsine
+
+	lsr				; double colors
+	and	#$7			; mask
+	tax
+	lda	colorlookup,X
+	sta	SAVEY
+
+	tya
+	ror
+	bcc	noshift
+	ror	SAVEY
+noshift:
+	lda	SAVEY
+;	and	#$7f
+	sta	(GBASL),Y
+
+	dey
+	bpl	create_xloop
+
+	dec	HGR_Y
+	bne	create_yloop
+
+	; X and Y both $FF
+
+	beq	draw_oval
+
+
+	;==============================
+	; calcsine
+	;==============================
+	; looks up sine of value in A
+	; accumulates it with ROW_SUM
+	; returns result in A
+	; Y preserved
+
+calcsine_div2:
+	lsr							; 2
+calcsine:
+	and	#$3f	; wrap sine at 63 entries		; 2
+
+	tax							; 2
+	cmp	#$20	; see if negative			; 2
+	bcc	sinadd						; 2/3
+
+sinsub:
+	; carry already set
+	lda	ROW_SUM						; 3
+	sbc	sinetable-32,X					; 4+
+	jmp	sindone						; 3
+
+sinadd:
+	; carry already clear
+	lda	ROW_SUM						; 3
+	adc	sinetable,X					; 4+
+
+sindone:
+	rts							; 6
+
+
+colorlookup:
+
+.byte $11,$55,$5d,$7f,$5d,$55,$11	; use 00 from sinetable
+;.byte $00
+
+sinetable:
+; this is actually (32*sin(x))
+
+.byte $00,$03,$06,$09,$0C,$0F,$11,$14
+.byte $16,$18,$1A,$1C,$1D,$1E,$1F,$1F
+.byte $20,$1F,$1F,$1E,$1D,$1C,$1A,$18
+.byte $16,$14,$11,$0F,$0C,$09,$06,$03