@@ -24,6 +24,15 @@ static Uint8 blending[4][16] = {

 	{1, 2, 3, 1, 1, 2, 3, 1, 1, 2, 3, 1, 1, 2, 3, 1},

 	{2, 3, 1, 2, 2, 3, 1, 2, 2, 3, 1, 2, 2, 3, 1, 2}};

+static void

+screen_change(UxnScreen *s, Uint16 x1, Uint16 y1, Uint16 x2, Uint16 y2)

+{

+	if(x1 < s->x1) s->x1 = x1;

+	if(y1 < s->y1) s->y1 = y1;

+	if(x2 > s->x2) s->x2 = x2;

+	if(y2 > s->y2) s->y2 = y2;

+}

+

 static void

 screen_fill(UxnScreen *s, Uint8 *pixels, Uint16 x1, Uint16 y1, Uint16 x2, Uint16 y2, Uint8 color)

 {

@@ -63,7 +72,7 @@ screen_palette(UxnScreen *p, Uint8 *addr)

 		p->palette[i] = 0x0f000000 | r << 16 | g << 8 | b;

 		p->palette[i] |= p->palette[i] << 4;

 	}

-	p->fg.changed = p->bg.changed = 1;

+	screen_change(&uxn_screen, 0, 0, p->width, p->height);

 }

 void

@@ -90,13 +99,19 @@ screen_resize(UxnScreen *p, Uint16 width, Uint16 height)

 void

 screen_redraw(UxnScreen *p)

 {

-	Uint32 i, size = p->width * p->height, palette[16], *pixels = p->pixels;

+	Uint32 i, x, y, w = p->width, palette[16], *pixels = p->pixels;

 	Uint8 *fg = p->fg.pixels, *bg = p->bg.pixels;

+	int x1 = p->x1, y1 = p->y1;

+	int x2 = p->x2 > p->width ? p->width : p->x2, y2 = p->y2 > p->height ? p->height : p->y2;

 	for(i = 0; i < 16; i++)

 		palette[i] = p->palette[(i >> 2) ? (i >> 2) : (i & 3)];

-	for(i = 0; i < size; i++)

-		pixels[i] = palette[fg[i] << 2 | bg[i]];

-	p->fg.changed = p->bg.changed = 0;

+	for(y = y1; y < y2; y++)

+		for(x = x1; x < x2; x++) {

+			i = x + y * w;

+			pixels[i] = palette[fg[i] << 2 | bg[i]];

+		}

+	p->x1 = p->y1 = 0xffff;

+	p->x2 = p->y2 = 0;

 }

 Uint8

@@ -134,7 +149,7 @@ screen_deo(Uint8 *ram, Uint8 *d, Uint8 port)

 			if(ctrl & 0x10) x2 = x, x = 0;

 			if(ctrl & 0x20) y2 = y, y = 0;

 			screen_fill(&uxn_screen, layer->pixels, x, y, x2, y2, color);

-			layer->changed = 1;

+			screen_change(&uxn_screen, x, y, x2, y2);

 		}

 		/* pixel mode */

 		else {

@@ -142,7 +157,7 @@ screen_deo(Uint8 *ram, Uint8 *d, Uint8 port)

 			Uint16 height = uxn_screen.height;

 			if(x < width && y < height)

 				layer->pixels[x + y * width] = color;

-			layer->changed = 1;

+			screen_change(&uxn_screen, x, y, x + 1, y + 1);

 			if(d[0x6] & 0x1) POKE2(d + 0x8, x + 1); /* auto x+1 */

 			if(d[0x6] & 0x2) POKE2(d + 0xa, y + 1); /* auto y+1 */

 		}

@@ -164,7 +179,7 @@ screen_deo(Uint8 *ram, Uint8 *d, Uint8 port)

 			screen_blit(&uxn_screen, layer->pixels, x + dy * i, y + dx * i, ram, addr, ctrl & 0xf, ctrl & 0x10, ctrl & 0x20, twobpp);

 			addr += (move & 0x04) << (1 + twobpp);

 		}

-		layer->changed = 1;

+		screen_change(&uxn_screen, x, y, x + dy * length + 8, y + dx * length + 8);

 		if(move & 0x1) POKE2(d + 0x8, x + dx); /* auto x+8 */

 		if(move & 0x2) POKE2(d + 0xa, y + dy); /* auto y+8 */

 		if(move & 0x4) POKE2(d + 0xc, addr);   /* auto addr+length */

@@ -11,12 +11,12 @@ WITH REGARD TO THIS SOFTWARE.

 */

 typedef struct Layer {

-	Uint8 *pixels, changed;

+	Uint8 *pixels;

 } Layer;

 typedef struct UxnScreen {

 	Uint32 palette[4], *pixels;

-	Uint16 width, height;

+	Uint16 width, height, x1, y1, x2, y2;

 	Layer fg, bg;

 } UxnScreen;

@@ -84,7 +84,7 @@ system_deo(Uxn *u, Uint8 *d, Uint8 port)

 		system_cmd(u->ram, PEEK2(d + 2));

 		break;

 	case 0x5:

-		if(PEEK2(d + 4)){

+		if(PEEK2(d + 4)) {

 			Uxn friend;

 			uxn_boot(&friend, u->ram);

 			uxn_eval(&friend, PEEK2(d + 4));

@@ -262,7 +262,7 @@ start(Uxn *u, char *rom, int queue)

 static void

 set_zoom(Uint8 z)

 {

-	if (z >= 1) {

+	if(z >= 1) {

 		zoom = z;

 		set_window_size(gWindow, (uxn_screen.width + PAD * 2) * zoom, (uxn_screen.height + PAD * 2) * zoom);

 	}

@@ -467,7 +467,7 @@ run(Uxn *u)

 			return 0;

 		screen_vector = PEEK2(&u->dev[0x20]);

 		uxn_eval(u, screen_vector);

-		if(uxn_screen.fg.changed || uxn_screen.bg.changed)

+		if(uxn_screen.x2)

 			redraw();

 		now = SDL_GetPerformanceCounter();

 		if(screen_vector) {