Anisotropic Filter

“But!” I hear you say, “Godot already has built in anisotropy!”

Well that only works if you stick with their built in ShaderMaterial3D. If you are doing custom effects, you will most likely want to add anisotropy to stop your pixels from swimming around distractingly.

Shader code

//Taken from https://www.shadertoy.com/view/ltXfRr

// --- alternate direct computation of ellipse geometry. Which is cheaper ? ( both have 5 sqrt +  5 div )
void ellips(in mat2 M, out vec2 A0, out vec2 A1, out float r0, out float r1) {
    vec2 I = M[0], J = M[1];                        // ellipse: P = cos(u).I + sin(u).J
    float a = ( dot(J,J) - dot(I,I) ) / dot (I,J),  // -> search for extrema of length(P)
          D = sqrt(a*a+4.),                         // get tan(u) -> s, c, axis*radii
          t0 = (a+D)/2., t1 = (a-D)/2.;
    A0 = (I + t0*J) / sqrt(1.+t0*t0);               // c = 1/sqrt(1+t²), s = t/sqrt(1+t²)
    A1 = (I + t1*J) / sqrt(1.+t1*t1);               // axis also encodes radius
    r0 = length(A0); A0 /= r0;
    r1 = length(A1); A1 /= r1;
    if (r1>r0){
		a=r0; r0=r1; r1=a;
		 I=A0;A0=A1;A1=I;    // sort eigenV
		}

}
// --- compute texture average on pixel footprint
vec4 anisotropic(sampler2D T, vec2 viewSize, vec2 uv) {
	float s = float(sampleCount);
    mat2 J = mat2(dFdx(uv), dFdy(uv));       // dFdxy: pixel footprint in texture space
    vec2 A,a; float M,m,l;
    ellips(J, A,a,M,m);
    A *= M;
    l = log2( m * viewSize.y );                            // MIPmap level corresponding to min radius
    //if (M/m>s) l = log2(M/s*R.y);               // optional
    vec4 O = vec4(0);
	float halfS = s / 2.0;
    for (float i = -halfS + 0.5; i<halfS; i++)                 // sample x16 along main axis at LOD min-radius
        O += textureLod(T, uv+(i/s)*A, l);
    return O/s;
}

Tags