New update:

- Added Paint filter.
 - Tweaked order of shaders.
 - Allow more grain parameters to be configured.

shaders/glsl/mfx_paint_pass1.fp

@@ -0,0 +1,52 @@
+/*
+   Paint filter from MariENB (first pass Kuwahara filter)
+   (C)2012-2021 Marisa Kirisame
+*/
+
+void main()
+{
+	vec2 coord = TexCoord;
+	vec4 res = texture(InputTexture,coord);
+	vec2 bresl = textureSize(InputTexture,0);
+	vec2 bof = 1./bresl;
+	float n = 16.;
+	vec3 m[4] = vec3[](vec3(0.),vec3(0.),vec3(0.),vec3(0.)),
+		s[4] = vec3[](vec3(0.),vec3(0.),vec3(0.),vec3(0.)),
+		c;
+	int i, j;
+	for ( i=-3; i<=0; i++ ) for ( j=-3; j<=0; j++ )
+	{
+		c = texture(InputTexture,coord+vec2(i,j)*bof).rgb;
+		m[0] += c;
+		s[0] += c*c;
+	}
+	for ( i=-3; i<=0; i++ ) for ( j=0; j<=3; j++ )
+	{
+		c = texture(InputTexture,coord+vec2(i,j)*bof).rgb;
+		m[1] += c;
+		s[1] += c*c;
+	}
+	for ( i=0; i<=3; i++ ) for ( j=-3; j<=0; j++ )
+	{
+		c = texture(InputTexture,coord+vec2(i,j)*bof).rgb;
+		m[2] += c;
+		s[2] += c*c;
+	}
+	for ( i=0; i<=3; i++ ) for ( j=0; j<=3; j++ )
+	{
+		c = texture(InputTexture,coord+vec2(i,j)*bof).rgb;
+		m[3] += c;
+		s[3] += c*c;
+	}
+	float min_sigma2 = 1e+2, sigma2;
+	for ( i=0; i<4; i++ )
+	{
+		m[i] /= n;
+		s[i] = abs(s[i]/n-m[i]*m[i]);
+		sigma2 = s[i].r+s[i].g+s[i].b;
+		if ( sigma2 >= min_sigma2 ) continue;
+		min_sigma2 = sigma2;
+		res.rgb = m[i];
+	}
+	FragColor = res;
+}