1. A shadowing subsystem of a ray tracing system implemented on a grid structure of cells, comprising: one or more processors with memory, a data structure of a scene, based on a grid of cells, a volumetric shadow stencil map at each cell having registration of all light blocking objects; wherein in run time, for each light source in the scene each hit point in each cell is tested for shadowing by analyzing its surrounding fragments at the stencil map; while in the case of a shadow uncertainty, intersection tests are performed with the light blocking objects.