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full SDF code:

float sdGoursat(vec3 position, float radius) // 0 <= radius < .75 { float p4 = dot(position * position, position * position); float p2 = dot(position, position); // f(x,y,z) = x^4 + y^4 + z^4 - x^2 - y^2 - z^2 + radius float f = p4 - p2 + radius; // ∇f(x,y,z) = {4x^3 - 2x, 4y^3 - 2y, 4z^3 - 2z} vec3 df = 4. * position * position * position - 2. * position; return max(min(.7 * f / length(df), .1), length(position) - 1.7); } float map(in vec3 position) { return sdGoursat(position / 45., 5. / 12.) * 45.; }