diff --git a/Makefile b/Makefile
index a7b23a8..33cb62a 100644
--- a/Makefile
+++ b/Makefile
@@ -249,7 +249,7 @@ bin/menu.o: src/menu.c $(TIC80_H) $(TIC_H)
 bin/surf.o: src/surf.c $(TIC80_H) $(TIC_H)
 	$(CC) $< $(OPT) $(INCLUDES) -c -o $@
 
-bin/system.o: src/system.c src/keycodes.c $(TIC80_H) $(TIC_H)
+bin/system.o: src/system.c src/keycodes.c src/ext/shader/* $(TIC80_H) $(TIC_H)
 	$(CC) $< $(OPT) $(INCLUDES) -c -o $@
 
 SDL_NET = \
diff --git a/src/ext/shader/crt-lottes.frag b/src/ext/shader/crt-lottes.frag
index aa7fe10..76a4708 100644
--- a/src/ext/shader/crt-lottes.frag
+++ b/src/ext/shader/crt-lottes.frag
@@ -4,12 +4,15 @@ precision highp float;
 
 varying vec2 texCoord;
 uniform sampler2D source;
+uniform float trg_x;
+uniform float trg_y;
 uniform float trg_w;
 uniform float trg_h;
+uniform float scr_w;
+uniform float scr_h;
 
 // Emulated input resolution.
 vec2 res=vec2(256.0,144.0);
-vec2 trg=vec2(trg_w, trg_h);
 
 // Hardness of scanline.
 //  -8.0 = soft
@@ -45,83 +48,86 @@ vec3 ToSrgb(vec3 c){return vec3(ToSrgb1(c.r),ToSrgb1(c.g),ToSrgb1(c.b));}
 // Nearest emulated sample given floating point position and texel offset.
 // Also zero's off screen.
 vec3 Fetch(vec2 pos,vec2 off){
-  pos=(floor(pos*res+off)+vec2(0.5,0.5))/res;
-  return ToLinear(1.2 * texture2D(source,pos.xy,-16.0).rgb);}
+	pos=(floor(pos*res+off)+vec2(0.5,0.5))/res;
+	return ToLinear(1.2 * texture2D(source,pos.xy,-16.0).rgb);}
 
 // Distance in emulated pixels to nearest texel.
 vec2 Dist(vec2 pos){pos=pos*res;return -((pos-floor(pos))-vec2(0.5));}
-    
+		
 // 1D Gaussian.
 float Gaus(float pos,float scale){return exp2(scale*pos*pos);}
 
 // 3-tap Gaussian filter along horz line.
 vec3 Horz3(vec2 pos,float off){
-  vec3 b=Fetch(pos,vec2(-1.0,off));
-  vec3 c=Fetch(pos,vec2( 0.0,off));
-  vec3 d=Fetch(pos,vec2( 1.0,off));
-  float dst=Dist(pos).x;
-  // Convert distance to weight.
-  float scale=hardPix;
-  float wb=Gaus(dst-1.0,scale);
-  float wc=Gaus(dst+0.0,scale);
-  float wd=Gaus(dst+1.0,scale);
-  // Return filtered sample.
-  return (b*wb+c*wc+d*wd)/(wb+wc+wd);}
+	vec3 b=Fetch(pos,vec2(-1.0,off));
+	vec3 c=Fetch(pos,vec2( 0.0,off));
+	vec3 d=Fetch(pos,vec2( 1.0,off));
+	float dst=Dist(pos).x;
+	// Convert distance to weight.
+	float scale=hardPix;
+	float wb=Gaus(dst-1.0,scale);
+	float wc=Gaus(dst+0.0,scale);
+	float wd=Gaus(dst+1.0,scale);
+	// Return filtered sample.
+	return (b*wb+c*wc+d*wd)/(wb+wc+wd);}
 
 // 5-tap Gaussian filter along horz line.
 vec3 Horz5(vec2 pos,float off){
-  vec3 a=Fetch(pos,vec2(-2.0,off));
-  vec3 b=Fetch(pos,vec2(-1.0,off));
-  vec3 c=Fetch(pos,vec2( 0.0,off));
-  vec3 d=Fetch(pos,vec2( 1.0,off));
-  vec3 e=Fetch(pos,vec2( 2.0,off));
-  float dst=Dist(pos).x;
-  // Convert distance to weight.
-  float scale=hardPix;
-  float wa=Gaus(dst-2.0,scale);
-  float wb=Gaus(dst-1.0,scale);
-  float wc=Gaus(dst+0.0,scale);
-  float wd=Gaus(dst+1.0,scale);
-  float we=Gaus(dst+2.0,scale);
-  // Return filtered sample.
-  return (a*wa+b*wb+c*wc+d*wd+e*we)/(wa+wb+wc+wd+we);}
+	vec3 a=Fetch(pos,vec2(-2.0,off));
+	vec3 b=Fetch(pos,vec2(-1.0,off));
+	vec3 c=Fetch(pos,vec2( 0.0,off));
+	vec3 d=Fetch(pos,vec2( 1.0,off));
+	vec3 e=Fetch(pos,vec2( 2.0,off));
+	float dst=Dist(pos).x;
+	// Convert distance to weight.
+	float scale=hardPix;
+	float wa=Gaus(dst-2.0,scale);
+	float wb=Gaus(dst-1.0,scale);
+	float wc=Gaus(dst+0.0,scale);
+	float wd=Gaus(dst+1.0,scale);
+	float we=Gaus(dst+2.0,scale);
+	// Return filtered sample.
+	return (a*wa+b*wb+c*wc+d*wd+e*we)/(wa+wb+wc+wd+we);}
 
 // Return scanline weight.
 float Scan(vec2 pos,float off){
-  float dst=Dist(pos).y;
-  return Gaus(dst+off,hardScan);}
+	float dst=Dist(pos).y;
+	return Gaus(dst+off,hardScan);}
 
 // Allow nearest three lines to effect pixel.
 vec3 Tri(vec2 pos){
-  vec3 a=Horz3(pos,-1.0);
-  vec3 b=Horz5(pos, 0.0);
-  vec3 c=Horz3(pos, 1.0);
-  float wa=Scan(pos,-1.0);
-  float wb=Scan(pos, 0.0);
-  float wc=Scan(pos, 1.0);
-  return a*wa+b*wb+c*wc;}
+	vec3 a=Horz3(pos,-1.0);
+	vec3 b=Horz5(pos, 0.0);
+	vec3 c=Horz3(pos, 1.0);
+	float wa=Scan(pos,-1.0);
+	float wb=Scan(pos, 0.0);
+	float wc=Scan(pos, 1.0);
+	return a*wa+b*wb+c*wc;}
 
 // Distortion of scanlines, and end of screen alpha.
 vec2 Warp(vec2 pos){
-  pos=pos*2.0-1.0;    
-  pos*=vec2(1.0+(pos.y*pos.y)*warp.x,1.0+(pos.x*pos.x)*warp.y);
-  return pos*0.5+0.5;}
+	pos=pos*2.0-1.0;    
+	pos*=vec2(1.0+(pos.y*pos.y)*warp.x,1.0+(pos.x*pos.x)*warp.y);
+	return pos*0.5+0.5;}
 
 // Shadow mask.
 vec3 Mask(vec2 pos){
-  pos.x+=pos.y*3.0;
-  vec3 mask=vec3(maskDark,maskDark,maskDark);
-  pos.x=fract(pos.x/6.0);
-  if(pos.x<0.333)mask.r=maskLight;
-  else if(pos.x<0.666)mask.g=maskLight;
-  else mask.b=maskLight;
-  return mask;}    
+	pos.x+=pos.y*3.0;
+	vec3 mask=vec3(maskDark,maskDark,maskDark);
+	pos.x=fract(pos.x/6.0);
+	if(pos.x<0.333)mask.r=maskLight;
+	else if(pos.x<0.666)mask.g=maskLight;
+	else mask.b=maskLight;
+	return mask;}    
 
 void main() {
-    vec2 pos = gl_FragCoord.xy/trg.xy;
-    hardScan=-12.0;
-//      maskDark=maskLight;
-    pos=Warp(gl_FragCoord.xy/trg.xy);
-    gl_FragColor.rgb=Tri(vec2(pos.s, 1.0 - pos.t))*Mask(gl_FragCoord.xy);
-  gl_FragColor = vec4(ToSrgb(gl_FragColor.rgb), 1.0);
+	hardScan=-12.0;
+//  maskDark=maskLight;
+	vec2 start=gl_FragCoord.xy-vec2(trg_x, trg_y);
+	start.y=scr_h-start.y;
+
+	vec2 pos=Warp(start/vec2(trg_w, trg_h));
+
+	gl_FragColor.rgb=Tri(pos)*Mask(gl_FragCoord.xy);
+	gl_FragColor = vec4(ToSrgb(gl_FragColor.rgb), 1.0);
 })
\ No newline at end of file
diff --git a/src/system.c b/src/system.c
index da95572..816f9f2 100644
--- a/src/system.c
+++ b/src/system.c
@@ -23,6 +23,8 @@ static struct
 {
 	Studio* studio;
 
+	bool useShader;
+
 	SDL_Window* window;
 	SDL_Renderer* renderer;
 	SDL_Texture* texture;
@@ -213,45 +215,60 @@ static void initTouchGamepad()
 }
 
 static void calcTextureRect(SDL_Rect* rect)
-{
-	s32 w, h;
-	SDL_GetWindowSize(platform.window, &w, &h);
-
-	rect->x = OFFSET_LEFT * w / TIC80_FULLWIDTH;
-	rect->y = OFFSET_TOP * h / TIC80_FULLHEIGHT;
-	rect->w = TIC80_WIDTH * w / TIC80_FULLWIDTH;
-	rect->h = TIC80_HEIGHT * h / TIC80_FULLHEIGHT;
-}
-
-static void calcTextureRect2(SDL_Rect* rect)
 {
 	SDL_GetWindowSize(platform.window, &rect->w, &rect->h);
 
-	if (rect->w * TIC80_HEIGHT < rect->h * TIC80_WIDTH)
+	if(platform.useShader)
 	{
-		s32 discreteWidth = rect->w - rect->w % TIC80_WIDTH;
-		s32 discreteHeight = TIC80_HEIGHT * discreteWidth / TIC80_WIDTH;
+		enum{Width = TIC80_FULLWIDTH, Height = TIC80_FULLHEIGHT};
 
-		rect->x = (rect->w - discreteWidth) / 2;
+		if (rect->w * Height < rect->h * Width)
+		{
+			rect->x = 0;
+			rect->y = 0;
 
-		rect->y = rect->w > rect->h 
-			? (rect->h - discreteHeight) / 2 
-			: OFFSET_LEFT*discreteWidth/TIC80_WIDTH;
+			rect->h = Height * rect->w / Width;
+		}
+		else
+		{
+			s32 width = Width * rect->h / Height;
 
-		rect->w = discreteWidth;
-		rect->h = discreteHeight;
+			rect->x = (rect->w - width) / 2;
+			rect->y = 0;
 
+			rect->w = width;
+		}
 	}
 	else
 	{
-		s32 discreteHeight = rect->h - rect->h % TIC80_HEIGHT;
-		s32 discreteWidth = TIC80_WIDTH * discreteHeight / TIC80_HEIGHT;
+		enum{Width = TIC80_WIDTH, Height = TIC80_HEIGHT};
 
-		rect->x = (rect->w - discreteWidth) / 2;
-		rect->y = (rect->h - discreteHeight) / 2;
+		if (rect->w * Height < rect->h * Width)
+		{
+			s32 discreteWidth = rect->w - rect->w % Width;
+			s32 discreteHeight = Height * discreteWidth / Width;
 
-		rect->w = discreteWidth;
-		rect->h = discreteHeight;
+			rect->x = (rect->w - discreteWidth) / 2;
+
+			rect->y = rect->w > rect->h 
+				? (rect->h - discreteHeight) / 2 
+				: OFFSET_TOP*discreteWidth/Width;
+
+			rect->w = discreteWidth;
+			rect->h = discreteHeight;
+
+		}
+		else
+		{
+			s32 discreteHeight = rect->h - rect->h % Height;
+			s32 discreteWidth = Width * discreteHeight / Height;
+
+			rect->x = (rect->w - discreteWidth) / 2;
+			rect->y = (rect->h - discreteHeight) / 2;
+
+			rect->w = discreteWidth;
+			rect->h = discreteHeight;
+		}
 	}
 }
 
@@ -268,8 +285,16 @@ static void processMouse()
 		SDL_Rect rect = {0, 0, 0, 0};
 		calcTextureRect(&rect);
 
-		if(rect.w) input->mouse.x = (mx - rect.x) * TIC80_WIDTH / rect.w;
-		if(rect.h) input->mouse.y = (my - rect.y) * TIC80_HEIGHT / rect.h;
+		if(platform.useShader)
+		{
+			if(rect.w) input->mouse.x = (mx - rect.x) * TIC80_FULLWIDTH / rect.w - OFFSET_LEFT;
+			if(rect.h) input->mouse.y = (my - rect.y) * TIC80_FULLHEIGHT / rect.h - OFFSET_TOP;
+		}
+		else
+		{
+			if(rect.w) input->mouse.x = (mx - rect.x) * TIC80_WIDTH / rect.w;
+			if(rect.h) input->mouse.y = (my - rect.y) * TIC80_HEIGHT / rect.h;
+		}
 	}
 
 	{
@@ -659,6 +684,14 @@ static void blitTexture()
 	}
 }
 
+// static void blitGpuTexture(GPU_Target* screen, GPU_Image* texture)
+// {
+// 	SDL_Rect rect = {0, 0, 0, 0};
+// 	calcTextureRect(&rect);
+
+// 	GPU_BlitScale(texture, NULL, platform.gpu.screen, rect.x, rect.y, (float)rect.w / TIC80_FULLWIDTH, (float)rect.h / TIC80_FULLHEIGHT);
+// }
+
 static void blitGpuTexture(GPU_Target* screen, GPU_Image* texture)
 {
 	SDL_Rect rect = {0, 0, 0, 0};
@@ -1057,13 +1090,31 @@ static void gpuTick()
 		GPU_UpdateImageBytes(platform.gpu.texture, NULL, (const u8*)tic->screen, TIC80_FULLWIDTH * sizeof(u32));
 
 		{
-			s32 w, h;
-			SDL_GetWindowSize(platform.window, &w, &h);
 
-			GPU_SetUniformf(GPU_GetUniformLocation(platform.gpu.crt_shader, "trg_w"), w);
-			GPU_SetUniformf(GPU_GetUniformLocation(platform.gpu.crt_shader, "trg_h"), h);
+			if(platform.useShader)
+			{
+				SDL_Rect rect = {0, 0, 0, 0};
+				calcTextureRect(&rect);
+
+				GPU_SetUniformf(GPU_GetUniformLocation(platform.gpu.crt_shader, "trg_x"), rect.x);
+				GPU_SetUniformf(GPU_GetUniformLocation(platform.gpu.crt_shader, "trg_y"), rect.y);
+				GPU_SetUniformf(GPU_GetUniformLocation(platform.gpu.crt_shader, "trg_w"), rect.w);
+				GPU_SetUniformf(GPU_GetUniformLocation(platform.gpu.crt_shader, "trg_h"), rect.h);
+
+				{
+					s32 w, h;
+					SDL_GetWindowSize(platform.window, &w, &h);
+					GPU_SetUniformf(GPU_GetUniformLocation(platform.gpu.crt_shader, "scr_w"), w);
+					GPU_SetUniformf(GPU_GetUniformLocation(platform.gpu.crt_shader, "scr_h"), h);
+				}
+
+				GPU_BlitScale(platform.gpu.texture, NULL, platform.gpu.screen, rect.x, rect.y, (float)rect.w / TIC80_FULLWIDTH, (float)rect.h / TIC80_FULLHEIGHT);
+			}
+			else
+			{
+				blitGpuTexture(platform.gpu.screen, platform.gpu.texture);				
+			}
 
-			GPU_BlitScale(platform.gpu.texture, NULL, platform.gpu.screen, 0, 0, (float)w / TIC80_FULLWIDTH, (float)h / TIC80_FULLHEIGHT);
 		}
 	}
 
@@ -1124,13 +1175,11 @@ static void emsGpuTick()
 
 u32 load_shader_program()
 {
-	Uint32 v, f;
-
 	static const char* VertexShader = 
 		#include "ext/shader/common.vert"
 	;
 
-	v = GPU_CompileShader(GPU_VERTEX_SHADER, VertexShader);
+	u32 v = GPU_CompileShader(GPU_VERTEX_SHADER, VertexShader);
 	
 	if(!v)
 		GPU_LogError("Failed to load vertex shader: %s\n", GPU_GetShaderMessage());
@@ -1139,7 +1188,7 @@ u32 load_shader_program()
 		#include "ext/shader/crt-lottes.frag"
 	;
 
-	f = GPU_CompileShader(GPU_PIXEL_SHADER, PixelShader);
+	u32 f = GPU_CompileShader(GPU_PIXEL_SHADER, PixelShader);
 	
 	if(!f)
 		GPU_LogError("Failed to load fragment shader: %s\n", GPU_GetShaderMessage());
@@ -1189,7 +1238,10 @@ static s32 start(s32 argc, char **argv, const char* folder)
 	GPU_SetAnchor(platform.gpu.texture, 0, 0);
 	GPU_SetImageFilter(platform.gpu.texture, GPU_FILTER_NEAREST);
 
-	platform.gpu.crt_shader = load_shader_program();
+	platform.useShader = true;
+
+	if(platform.useShader)
+		platform.gpu.crt_shader = load_shader_program();
 
 #if defined(__EMSCRIPTEN__)