UniQuadrix is a simple graphics modeling program for objects represented as the intersection of quadric and planar half-spaces. It runs under the 4.2 BSD UNIX operating system on the DEC VAX superminicomputer and the M68000-based Sun Workstation. The program accepts scene descriptions in a language much like that of Unigrafix, a polygon-based modeler developed at UC Berkeley, and generates black-and-white, smooth-shaded, smooth-edged images on several output devices. UniQuadrix uses implicit equations to represent the surfaces and boundaries of objects throughout the rendering process. This allows a "scanline" hidden surface algorithm to efficiently identify visible "spans". The algorithm exploits scan line as well as object coherence. An efficient incremental algorithm shades pixels within spans. Images of one hundred half-spaces with one-million shaded pixels commonly require three minutes of VAX time.