@@ -19,6 +19,14 @@ static Uint8 blending[5][16] = {

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

 	{1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 0}};

+void

+ppu_frame(Ppu *p)

+{

+	p->redraw = 0;

+	p->i0 = p->width / PPW + p->height * p->stride;

+	p->i1 = 0;

+}

+

 static void

 ppu_clear(Ppu *p)

 {

@@ -27,55 +35,55 @@ ppu_clear(Ppu *p)

 		p->dat[i] = 0;

 }

-unsigned int

+void

 ppu_pixel(Ppu *p, int fg, Uint16 x, Uint16 y, Uint8 color)

 {

-	unsigned int ret, i = x / PPW + y * p->stride, shift = x % PPW * 4;

+	unsigned int v, i = x / PPW + y * p->stride, shift = x % PPW * 4;

 	if(x >= p->width || y >= p->height)

-		return 0;

-	ret = p->dat[i];

+		return;

+	v = p->dat[i];

 	if(fg) shift += 2;

 	p->dat[i] &= ~(3 << shift);

 	p->dat[i] |= color << shift;

-	return ret ^ p->dat[i];

+	if((v ^ p->dat[i]) != 0){

+		p->redraw = 1;

+		p->i0 = p->i0 < i ? p->i0 : i;

+		p->i1 = p->i1 > i ? p->i1 : i;

+	}

 }

-unsigned int

+void

 ppu_1bpp(Ppu *p, int fg, Uint16 x, Uint16 y, Uint8 *sprite, Uint8 color, Uint8 flipx, Uint8 flipy)

 {

 	Uint16 v, h;

-	int ret = 0;

 	for(v = 0; v < 8; v++)

 		for(h = 0; h < 8; h++) {

 			Uint8 ch1 = (sprite[v] >> (7 - h)) & 0x1;

 			if(ch1 || blending[4][color])

-				ret |= ppu_pixel(p,

+				ppu_pixel(p,

 					fg,

 					x + (flipx ? 7 - h : h),

 					y + (flipy ? 7 - v : v),

 					blending[ch1][color]);

 		}

-	return ret;

 }

-unsigned int

+void

 ppu_2bpp(Ppu *p, int fg, Uint16 x, Uint16 y, Uint8 *sprite, Uint8 color, Uint8 flipx, Uint8 flipy)

 {

 	Uint16 v, h;

-	int ret = 0;

 	for(v = 0; v < 8; v++)

 		for(h = 0; h < 8; h++) {

 			Uint8 ch1 = ((sprite[v] >> (7 - h)) & 0x1);

 			Uint8 ch2 = ((sprite[v + 8] >> (7 - h)) & 0x1);

 			Uint8 ch = ch1 + ch2 * 2;

 			if(ch || blending[4][color])

-				ret |= ppu_pixel(p,

+				ppu_pixel(p,

 					fg,

 					x + (flipx ? 7 - h : h),

 					y + (flipy ? 7 - v : v),

 					blending[ch][color]);

 		}

-	return ret;

 }

 /* output */

@@ -89,5 +97,6 @@ ppu_set_size(Ppu *p, Uint16 width, Uint16 height)

 	p->dat = realloc(p->dat, p->stride * p->height * sizeof(unsigned int));

 	if(p->dat == NULL) return 0;

 	ppu_clear(p);

+	ppu_frame(p);

 	return 1;

-}

\ No newline at end of file

+}

@@ -23,10 +23,12 @@ typedef unsigned int Uint32;

 typedef struct Ppu {

 	Uint16 width, height;

+	int i0, i1, redraw;

 	unsigned int *dat, stride;

 } Ppu;

+void ppu_frame(Ppu *p);

 int ppu_set_size(Ppu *p, Uint16 width, Uint16 height);

-unsigned int ppu_pixel(Ppu *p, int fg, Uint16 x, Uint16 y, Uint8 color);

-unsigned int ppu_1bpp(Ppu *p, int fg, Uint16 x, Uint16 y, Uint8 *sprite, Uint8 color, Uint8 flipx, Uint8 flipy);

-unsigned int ppu_2bpp(Ppu *p, int fg, Uint16 x, Uint16 y, Uint8 *sprite, Uint8 color, Uint8 flipx, Uint8 flipy);

+void ppu_pixel(Ppu *p, int fg, Uint16 x, Uint16 y, Uint8 color);

+void ppu_1bpp(Ppu *p, int fg, Uint16 x, Uint16 y, Uint8 *sprite, Uint8 color, Uint8 flipx, Uint8 flipy);

+void ppu_2bpp(Ppu *p, int fg, Uint16 x, Uint16 y, Uint8 *sprite, Uint8 color, Uint8 flipx, Uint8 flipy);

@@ -122,17 +122,25 @@ get_pixel(int x, int y)

 static void

 redraw(Uxn *u)

 {

-	Uint16 x, y;

+	Uint16 x, y, y0 = 0, y1 = ppu.height;

+	SDL_Rect up = gRect;

 	if(devsystem->dat[0xe])

 		inspect(&ppu, u->wst.dat, u->wst.ptr, u->rst.ptr, u->ram.dat);

-	for(y = 0; y < ppu.height; ++y)

+	if(ppu.redraw) {

+		y0 = ppu.i0 / ppu.stride;

+		y1 = ppu.i1 / ppu.stride + 1;

+		up.y += y0;

+		up.h = y1 - y0;

+	}

+	for(y = y0; y < y1; ++y)

 		for(x = 0; x < ppu.width; ++x)

 			ppu_screen[x + y * ppu.width] = palette[get_pixel(x, y)];

-	SDL_UpdateTexture(gTexture, &gRect, ppu_screen, ppu.width * sizeof(Uint32));

+	SDL_UpdateTexture(gTexture, &up, ppu_screen + y0 * ppu.width, ppu.width * sizeof(Uint32));

 	SDL_RenderClear(gRenderer);

 	SDL_RenderCopy(gRenderer, gTexture, NULL, NULL);

 	SDL_RenderPresent(gRenderer);

 	reqdraw = 0;

+	ppu_frame(&ppu);

 }

 static void

@@ -353,7 +361,7 @@ screen_talk(Device *d, Uint8 b0, Uint8 w)

 			Uint16 x = peek16(d->dat, 0x8);

 			Uint16 y = peek16(d->dat, 0xa);

 			Uint8 layer = d->dat[0xe] & 0x40;

-			reqdraw |= ppu_pixel(&ppu, layer, x, y, d->dat[0xe] & 0x3);

+			ppu_pixel(&ppu, layer, x, y, d->dat[0xe] & 0x3);

 			if(d->dat[0x6] & 0x01) poke16(d->dat, 0x8, x + 1); /* auto x+1 */

 			if(d->dat[0x6] & 0x02) poke16(d->dat, 0xa, y + 1); /* auto y+1 */

 			break;

@@ -364,10 +372,10 @@ screen_talk(Device *d, Uint8 b0, Uint8 w)

 			Uint8 layer = d->dat[0xf] & 0x40;

 			Uint8 *addr = &d->mem[peek16(d->dat, 0xc)];

 			if(d->dat[0xf] & 0x80) {

-				reqdraw |= ppu_2bpp(&ppu, layer, x, y, addr, d->dat[0xf] & 0xf, d->dat[0xf] & 0x10, d->dat[0xf] & 0x20);

+				ppu_2bpp(&ppu, layer, x, y, addr, d->dat[0xf] & 0xf, d->dat[0xf] & 0x10, d->dat[0xf] & 0x20);

 				if(d->dat[0x6] & 0x04) poke16(d->dat, 0xc, peek16(d->dat, 0xc) + 16); /* auto addr+16 */

 			} else {

-				reqdraw |= ppu_1bpp(&ppu, layer, x, y, addr, d->dat[0xf] & 0xf, d->dat[0xf] & 0x10, d->dat[0xf] & 0x20);

+				ppu_1bpp(&ppu, layer, x, y, addr, d->dat[0xf] & 0xf, d->dat[0xf] & 0x10, d->dat[0xf] & 0x20);

 				if(d->dat[0x6] & 0x04) poke16(d->dat, 0xc, peek16(d->dat, 0xc) + 8); /* auto addr+8 */

 			}

 			if(d->dat[0x6] & 0x01) poke16(d->dat, 0x8, x + 8); /* auto x+8 */

@@ -529,7 +537,7 @@ run(Uxn *u)

 			}

 		}

 		uxn_eval(u, peek16(devscreen->dat, 0));

-		if(reqdraw || devsystem->dat[0xe])

+		if(reqdraw || ppu.redraw || devsystem->dat[0xe])

 			redraw(u);

 		if(!BENCH) {

 			elapsed = (SDL_GetPerformanceCounter() - start) / (double)SDL_GetPerformanceFrequency() * 1000.0f;