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games/md: interlacing, sort of

--- a/sys/src/games/md/dat.h

+++ b/sys/src/games/md/dat.h

@@ -23,7 +23,7 @@

 extern u16int vram[32768], vsram[40];

 extern u32int cramc[64];

 extern u16int vdpstat;

-extern int vdpx, vdpy;

+extern int vdpx, vdpy, frame, intla;

 extern u8int ym[512], ymstat;

--- a/sys/src/games/md/mem.c

+++ b/sys/src/games/md/mem.c

@@ -180,6 +180,8 @@

 				v = vdpx - (vdpx >= 360 ? 406 : 0);

 			else

 				v = vdpx - (vdpx >= 296 ? 342 : 0);

+			if(intla)

+				return vdpy - (vdpy >= 234 ? 5 : 0) << 8 & 0xfe00 | frame << 8 | v >> 1 & 0xff;

 			return vdpy - (vdpy >= 234 ? 5 : 0) << 8 | v >> 1 & 0xff;

 		default:

 			goto invalid;

--- a/sys/src/games/md/vdp.c

+++ b/sys/src/games/md/vdp.c

@@ -6,11 +6,12 @@

 u8int pic[320*224*4*3];

 u16int vdpstat = 0x3400;

-int vdpx, vdpy;

+int vdpx, vdpy, vdpyy, frame, intla;

 u16int hctr;

-static int xmax, xdisp, ymax = 262, yvbl = 234;

+static int xmax, xdisp;

 static int sx, snx, col, pri, lum;

 enum { DARK, NORM, BRIGHT };

+enum { ymax = 262, yvbl = 234 };

 void

 vdpmode(void)

@@ -22,6 +23,7 @@

 		xdisp = 256;

 		xmax = 342;

 	}

+	intla = (reg[MODE4] & 6) == 6;

 }

 static void

@@ -43,6 +45,8 @@

 	u.b[2] = v;

 	u.b[3] = 0;

 	if(scale == 2){

+		if(intla)

+			y = y << 1 | frame;

 		q = (u32int*)pic + (x + y * 320) * 2;

 		q[0] = u.w;

 		q[1] = u.w;

@@ -97,9 +101,15 @@

 	a += p->tx;

 	p->t = vram[a];

 	y = p->tny;

-	if((p->t & 0x1000) != 0)

-		y = 7 - y;

-	a = (p->t & 0x7ff) << 4 | y << 1;

+	if(intla){

+		if((p->t & 0x1000) != 0)

+			y = 15 - y;

+		a = (p->t & 0x7ff) << 5 | y << 1;

+	}else{

+		if((p->t & 0x1000) != 0)

+			y = 7 - y;

+		a = (p->t & 0x7ff) << 4 | y << 1;

+	}

 	p->c = vram[a] << 16 | vram[a+1];

 }

@@ -129,9 +139,15 @@

 		v = -(vram[a + i] & 0x3ff);

 		p->tnx = v & 7;

 		p->tx = v >> 3 & pctxt[i].w - 1;

-		v = vsram[i] + vdpy;

-		p->tny = v & 7;

-		p->ty = v >> 3 & pctxt[i].h - 1;

+		if(intla){

+			v = vsram[i] + vdpyy;

+			p->tny = v & 15;

+			p->ty = v >> 4 & pctxt[i].h - 1;

+		}else{

+			v = vsram[i] + vdpy;

+			p->tny = v & 7;

+			p->ty = v >> 3 & pctxt[i].h - 1;

+		}

 		tile(p);

 		if(p->tnx != 0)

 			if((p->t & 0x800) != 0)

@@ -237,9 +253,15 @@

 	np = 0;

 	nt = 0;

 	do{

-		q->y = (p[0] & 0x3ff) - 128;

-		q->h = (p[1] >> 8 & 3) + 1 << 3;

-		dy = vdpy - q->y;

+		if(intla){

+			q->y = (p[0] & 0x3ff) - 256;

+			q->h = (p[1] >> 8 & 3) + 1 << 4;

+			dy = vdpyy - q->y;

+		}else{

+			q->y = (p[0] & 0x3ff) - 128;

+			q->h = (p[1] >> 8 & 3) + 1 << 3;

+			dy = vdpy - q->y;

+		}

 		if(dy >= q->h)

 			continue;

 		q->t = p[2];

@@ -249,7 +271,7 @@

 		if(q->x == 0xff80)

 			break;

 		q->w = (p[1] >> 10 & 3) + 1 << 3;

-		c = ((q->t & 0x7ff) << 4) + (dy << 1);

+		c = ((q->t & 0x7ff) << 4+intla) + (dy << 1);

 		for(i = 0; i < q->w >> 3 && np < xdisp; i++){

 			v = vram[c] << 16 | vram[(u16int)(c+1)];

 			c += q->h << 1;

@@ -354,6 +376,8 @@

 			vdpstat &= ~(STATINT | STATVBL | STATOVR | STATCOLL);

 			flush();

 		}

+		if(intla)

+			vdpyy = vdpy << 1 | frame;

 		if(vdpy == 0 || vdpy >= 225)

 			hctr = reg[HORCTR];

 		else

@@ -364,6 +388,7 @@

 			}

 		if(vdpy == yvbl){

 			vdpstat |= STATVBL | STATINT;

+			frame ^= 1;

 			z80irq = 1;

 			if((reg[MODE2] & IE0) != 0)

 				irq |= INTVBL;