Eliminating invisible meshes before sending draw calls to the GPU:

Extract the 6 frustum planes (Left, Right, Bottom, Top, Near, Far) from the 4x4 View-Projection Matrix ($M = V \times P$):

// Distance from bounding sphere center to frustum plane
float DistanceToPlane(const Plane& p, const Vector3& center) {
    return p.a * center.x + p.b * center.y + p.c * center.z + p.d;
}

bool IsSphereInFrustum(const Vector3& center, float radius, const Plane planes[6]) {
    for (int i = 0; i < 6; i++) {
        if (DistanceToPlane(planes[i], center) < -radius)
            return false; // Completely outside frustum!
    }
    return true; // Visible!
}

Skips 60-80% of world scene objects, saving massive GPU rasterization time!

The plane extraction formula from the ViewProjection matrix is elegant and requires zero matrix inversion.

Vectorizing the 6 plane tests with AVX2 allows culling 50,000 objects in < 1 millisecond on CPU.