A new hidden feature algorithm in UNIGRAFIX was inspired by Hamlin and Gear's STACK algorithm. It is a scan-line, image space algorithm that exploits depth ordering of faces to produce the visible spans for each scanline. Detection and correct display of intersecting objects is efficiently achieved by checking only visible faces, and comparing each one with a minimal set of potential penetrators.
The resulting rendering program also features smooth shading of faces. It is robust and fast, and this makes it a good choice for interactive design where other renderers might fail or take too much time.