Clipping for Sprite and Billboard patches

When using Sprite and Billboard within a 3D Transformation patch, it isn't straightforward to determine if the Sprite/Billboard will be onscreen. Perhaps make a patch that, given the same positioning coordinates as a Sprite or Billboard, provides a boolean output indicating whether anything is onscreen? (i.e., you could then feed the output to an actual Sprite/Billboard's Enable input, to improve performances.)

See this thread for discussion: