; Twoerl v4 (with vsync and different palette)
; /mic, 2008 | micol972@gmail.com | http://jiggawatt.org/badc0de
;
; Press [ESC] to exit the program.
;
; How to compile:
;  nasm -o twoerl4.com twoerl4.asm
;


%define delta bp
%define temp bp+4
%define p1 0x300
%define p2 0x302
%define pos 0x304

[org 0x100]		

start:
mov 	al,0x13	
int 	0x10

mov	bp,0x200
mov	bh,0xF0
mov 	cx,0x100
@@setup_sine:
	mov 	word [bp],cx
	fild 	word [bp]
	fmul 	dword [foo]
	fsin
	fmul 	dword [foo+2]
	fistp 	word [bx]
	inc	bx
	inc	bx
	loop 	@@setup_sine

mov 	dx,0x3C8
xor 	ax,ax
xor 	bx,bx
out 	dx,al
inc 	dx
mov 	ch,1
@@1:
	mov	al,bl
	shr	al,2
	out 	dx,al
	xchg	al,ah
	out 	dx,al
	mov 	ax,bx
	cmp 	al,63
	jna 	@@2
	mov 	al,63
	@@2:
	out 	dx,al
	inc 	bx
	loop 	@@1

@@mainloop:
	push	0xa000
	pop	es

	mov 	ax,[pos]
	mov 	[p2],ax
	shl 	ax,8
	mov 	[p1],ax

	mov 	dx,0x3DA
	@@wait1:
		in 	ax,dx
		and 	al,8
		jnz 	short @@wait1
	@@wait2:
		in 	ax,dx
		and 	al,8
		jz 	short @@wait2
	
	mov 	si,0xF000

	xor 	di,di
	mov 	cl,200
	@@yloop:
		push 	cx

		movzx 	bx,byte [p1+1]
		add 	bx,bx
		mov 	ax,[bx+si]	; sa
		
		movzx 	bx,byte [p2]
		add 	bl,64
		add 	bx,bx
		mov 	dx,[bx+si]	; ca
		
		movzx 	bx,byte [pos]
		add 	bx,bx
		mov 	bp,[bx+si]	; t
		lea	ebp,[ebp+edx*8]
		sub	bp,dx
		
		mov	dx,ax
		sar 	dx,5
		
		mov 	al,cl
		
		push 	ax
		mov 	cl,128
		add     cx,dx
		mov	dx,320
		sub	dx,cx
		rep 	stosb
		
		mov 	cl,64
		@@xloop:
			mov 	ax,bp
			sar 	ax,8
			and 	ax,15
			sub 	al,7
			jns 	@@3
			neg 	al
			@@3:
			shl 	al,3
			stosb
			add 	bp,0x55
			loop 	@@xloop
		
		sub 	dl,64
		mov 	cx,dx
		pop 	ax
		rep 	stosb
		
		inc 	byte [p2]
		mov 	ax,[ddp]
		add 	word [p1],ax
		pop 	cx
		loop 	@@yloop
		
        inc 	word [pos]
	sar	bp,1
	mov 	[ddp],bp
 
	in 	al,60h
	dec 	al
	jnz 	@@mainloop

ret

foo:
dd 0x3CC90FDB
dw 0x4380 
ddp: