Play around with upscaling pixel filtering

shader/texture/antia.frag

@@ -3,19 +3,35 @@ in vec2 vTexPos;
 out vec4 fColor;
 layout (location = 0) uniform vec2 screensize;
 layout(binding = 0) uniform sampler2D screenTexture;
-float xoff = 2 / screensize.x;
-float yoff = 2 / screensize.y;
 vec3 f (float x, float y)
-{ return texture(screenTexture, vTexPos + vec2(x*xoff,y*yoff)).xyz; 
+//{ return texture(screenTexture, vTexPos + vec2((x+0.5)/screensize.x,(y+0.5)/screensize.y)).xyz; 
+{ return texture(screenTexture, vTexPos + vec2(x/screensize.x,y/screensize.y)).xyz; 
+}
+bool t (vec3 x, vec3 y)
+{ return dot(x-y,x-y) < 0.1;
+}
+bool t3 (vec3 x, vec3 y, vec3 z)
+{ return t(x,y) && t(y,z);
 }
 void main() 
 {
 vec3 tl = f(-1, 1);
-vec3 tt = f( 0, 1);
+vec3 tt = f( 0, 2);
 vec3 tr = f( 1, 1);
-vec3 mr = f( 1, 0);
+vec3 mr = f( 2, 0);
 vec3 br = f( 1,-1);
-    if (tl == tt && tt == tr && tr == mr && mr == br)
+vec3 bb = f( 0,-2);
+vec3 bl = f(-1,-1);
+vec3 ml = f(-2, 0);
+    if (t3(tt,tr,mr))
+        { fColor = vec4(tr,1);}
+    else if (t3(mr,br,bb))
+        { fColor = vec4(br,1);}
+    else if (t3(bb,bl,ml))
+        { fColor = vec4(bl,1);}
+    else if (t3(ml,tl,tt))
         { fColor = vec4(tl,1);}
-    else {fColor = texture(screenTexture, vTexPos); }
+    else 
+        //{fColor = texture(screenTexture, vTexPos); }
+        {fColor = vec4(f(0,0),1); }
 }