The union operator also produces incorrect distances for the interior of the union volume, which is a problem for things like shadow cone tracing. See http://iq

The union operator also produces incorrect distances for the interior of the union volume, which is a problem for things like shadow cone tracing. See http://iquilezles.org/www/articles/interiordistance/interiordistance.htm http://iquilezles.org/www/articles/interiordistance/interior..., I've actually been struggling with this in my SDF implementation. I'm still a big fan of the union operation since GPU rasterizers can trivially hardware accelerate it, which means you can render a bunch of objects in one go and know that it will be performed at near-optimal efficiency by the GPU. I've been combining that with a packing technique to render 3 depth slices at once in RGB (plus an extra duplicate slice in A) so that I can accurately sample any point in space with a single bilinear texture read.