  We present a novel method for the interactive construction and rendering of
extremely large molecular scenes, capable of representing multiple biological
cells in atomistic detail. Our method is tailored for scenes, which are
procedurally constructed, based on a given set of building rules. Rendering of
large scenes normally requires the entire scene available in-core, or
alternatively, it requires out-of-core management to load data into the memory
hierarchy as a part of the rendering loop. Instead of out-of-core memory
management, we propose to procedurally generate the scene on-demand on the fly.
The key idea is a positional- and view-dependent procedural scene-construction
strategy, where only a fraction of the atomistic scene around the camera is
available in the GPU memory at any given time. The atomistic detail is
populated into a uniform-space partitioning using a grid that covers the entire
scene. Most of the grid cells are not filled with geometry, only those are
populated that are potentially seen by the camera. The atomistic detail is
populated in a compute shader and its representation is connected with
acceleration data structures for hardware ray-tracing of modern GPUs. Objects
which are far away, where atomistic detail is not perceivable from a given
viewpoint, are represented by a triangle mesh mapped with a seamless texture,
generated from the rendering of geometry from atomistic detail. The algorithm
consists of two pipelines, the construction-compute pipeline, and the rendering
pipeline, which work together to render molecular scenes at an atomistic
resolution far beyond the limit of the GPU memory containing trillions of
atoms. We demonstrate our technique on multiple models of SARS-CoV-2 and the
red blood cell.
