Porting from BASIC

[stefano]

There are few differences to deal with, like the inverted Y coordinate when drawing graphics, but it is definitely possible

https://github.com/z88dk/z88dk/blob/mas ... /hangman.c

hangman.png

[stefano]

zx81 port, the one in the picture has an internal mod for memory expansion and wrx

[Timmy]

I've ported a relatively simple game from BASIC to C a while ago. The exercise is covered in these two threads over at WoS:

BASIC version: https://worldofspectrum.org/forums/disc ... e-tutorial

C version: https://worldofspectrum.org/forums/disc ... rial-z88dk

(No graphical commands, just simple character usage.)

[stefano]

interesting, you chose a C/asm mixture, surely a fun project.
I'm wondering if, in example, it could be ported to the zx81 in text mode., the scroll functions should be available.

[Timmy]

I'm wondering if, in example, it could be ported to the zx81 in text mode., the scroll functions should be available.

I remember someone saying in the basic thread that he wanted to port to zx81, but never did.

I personally know too little about the zx81 that I have no idea how to port it. I don't even know what emulator to use (at the moment of writing).

What do you mean by "scroll functions" by the way? Does the zx81 have specific scroll functions in z88dk?

[stefano]

Yes, it does, look at zx81.h.
By the way I remembered something better than the actual ones, horizontal scrolling is not available (while I think there's already something for the Spectrum and possibly the TS2068). The scroll down must be somewhat delicate, because I had trouble calling it from BASIC.
rollchr() is an impressive effect but does not have to do with scrolling.

[Timmy]

I'm wondering if, in example, it could be ported to the zx81 in text mode., the scroll functions should be available.

So I just spent a part of a weekend to do something...

(Now this could be better and smaller and use conio and other libraries, but this is quicker and it's enough for now.)

Code: Select all

#include <input.h>
#include <zx81.h>

int __FASTCALL__ scroll_left()
// works on all models, untested.
{
	#asm
	ld	hl,(16396)	; D_FILE
	inc	hl			
	
	ld b, 21		; scrolling 20 lines for now
	
.loop1
	ld a, (hl)
	cp 0x76
	jp z, empty_line
	
	ld d, h
	ld e, l		; de -> previous char
	inc hl		; hl -> current char
	
.first
	ld a, (hl)
	cp 0x76
	jr nz, copying
	
	ld a, 0
	ld (de), a		; fill last char with space
	jr empty_line
	
.copying
	ld (de), a
	inc de
	inc hl
	
	jr first
	
.empty_line

	inc hl
	djnz loop1
	
	#endasm
}

// combine 2 chars into 1 int
int combine(uchar y, uchar x)
{
	int p;
	p = (y<<8) + x;
	return p;
}


int __FASTCALL__ init_screen(uchar i)
{
	// fill the screen with spaces, so that i don't have to create new lines
	// does the same as filltxt, but i might decide to change resolution later
	#asm
	ld a, l
	ld hl,(16396)	; D_FILE
	inc	hl	
	
	ld b, 23		
	
.loop_init
	push bc
	ld b, 32
	
.loop_row1
	ld (hl), a
	inc hl
	djnz loop_row1
	
	ld (hl), 0x76
	inc hl
	pop bc

	djnz loop_init
	#endasm
}


int __FASTCALL__ zx81_saddr(int yx)
// only works for 4k+ models, and only after using filltxt
{
	#asm
	ld b, h
	ld c, l
	
	ld hl,(16396)	; D_FILE
	inc hl
	ld de, 33		; line size (might change later), this only works for 4k+ models

	ld a, b
	and a
	jr z, no_rows1
	
.loop_rows1
	add hl, de
	djnz loop_rows1
	
.no_rows1
	ld b, 0
	add hl, bc
	
	#endasm
}

void print_string(int address, uchar *string_address)
{
	uchar *s;
	int a;
	
	a = address;
	s = string_address;
	
	while (s[0]!=0x99)
	{
		bpoke(a, s[0]);
		s++;
		a++;
	}
}

void __CALLEE__ i16toa(uint number, char* dest)
{
	#asm

		pop bc
		pop de				; de = dest
		pop hl				; hl = number
		push bc

		ld bc,-10000
		call num1
		ld bc,-1000
		call num1
		ld bc,-100
		call num1
		ld c,-10
		call num1
		ld c,b

.num1	ld	a, 0x1c - 1	; '0'-1
.num2	inc	a

		add hl,bc
		jr c, num2
		sbc hl,bc

		ld (de),a
		inc de
		ret
	#endasm

}

int main()
{
	char y;
	int addr, bottom;
	char game_over;
	int score;
	char score_str[16] = { 0x38, 0x28, 0x34, 0x37, 0x2a, 0, 0xe, 0, 0x1c, 0x1c, 0x1c, 0x1c, 0x1c, 0, 0x99 }; // score string but now in zx81 chars, obviously can't end with 0 now.
	
	init_screen(0);
	
	y = 10;
	game_over = 0;
	score = 0;
	bottom = zx81_saddr(combine(21,0));
	
	while (!game_over)
	{
		scroll_left();
		
		i16toa(score, &(score_str[8]) );
		print_string(bottom, score_str);
		
		bpoke (zx81_saddr(combine(rand()%21,30)), 0x17); // '*'
		
		y = y + (in_Inkey()=='6') - (in_Inkey()=='7');
		y = y + (y<0)-(y>20);
		
		addr = zx81_saddr(combine(y,3));
		
		bpoke (addr, 0x12); // '>'	
		
		game_over = bpeek(addr+1) == 0x17;
		
		score = score + 10;
	}
	
	return score;
}

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