This document discusses software-defined and high-fidelity visualization rendering techniques that run exclusively on CPUs. It introduces OpenSWR, an open-source software rasterizer that provides a drop-in replacement for OpenGL, and OSPRay, a ray tracing library that is not limited by legacy APIs. OpenSWR implements a subset of OpenGL to work with existing visualization applications and focuses on performance through threading and vectorization. OSPRay allows for more flexibility in rendering capabilities but requires more effort for existing apps to use. Both aim to provide scalable, flexible CPU-based rendering that can run on various system types and sizes.