The problem of rendering3D graphics can be conceptually presented as finding all intersections between a set of "primitives" and a set of "rays". Up to 2010, all typical graphic acceleration boards, called graphics processing units, use rasterization algorithms. The ray tracing algorithm solves the rendering problem in a different way. In each step, it finds all intersections of a ray with a set of relevant primitives of the scene. Both approaches have their own benefits and drawbacks. Rasterization can be performed using devices based on a stream computing model, one triangle at the time, and access to the complete scene is needed only once. The drawback of rasterization is that non-local effects, required for an accurate simulation of a scene, such as reflections and shadows are difficult; and refractions nearly impossible to compute. The ray tracing algorithm is inherently suitable for scaling by parallelization of individual ray renders. However anything other than ray casting requires recursion of the ray tracing algorithm to complete their analysis, since reflected, refracted, and scattered rays require that various parts of the scene be re-accessed in a way not easily predicted. But it can easily compute various kinds of physically correct effects, providing much more realistic impression than rasterization. The complexity of a well implemented ray tracing algorithm scales logarithmically; this is due to objects being placed into BSP trees or similar structures, and only being analyzed if a ray intersects with the bounding volume of the binary space partition.
Implementations
Various implementations of ray tracing hardware have been created, both experimental and commercial:
Researchers at Princeton university proposed using DSPs to build a hardware unit for ray tracing acceleration, named "TigerSHARK".
ART VPS company, situated in the UK, sold ray tracing hardware for off-line rendering. The hardware used multiple specialized processors that accelerated ray-triangle intersection tests. Software provided integration with Autodesk Maya and Max data formats, and utilized the Renderman scene description language for sending data to the processors. As of 2010, ARTVPS no longer produces ray tracing hardware but continues to produce rendering software.
Siliconarts developed a dedicated real-time ray tracing hardware. RayCore, which is the world's first real-time ray tracing semiconductor IP, was announced.
Caustic Graphics have produced a plug in card, the "CausticOne", that accelerates global illumination and other ray based rendering processes when coupled to a PC CPU and GPU. The hardware is designed to organize scattered rays into more coherent sets for further processing by an external processor.
Imagination Technologies, after acquiring Caustic Graphics, produced the Caustic Professional's R2500 and R2100 plug in cards containing RT2 ray trace units. Each RTU was capable of calculating up to 50 million incoherent rays per second.
Nvidia, partnering with Microsoft DirectX, announced the Nvidia RTX developer library in 2018, which promised fast real-time ray tracing solutions powered by hardware accelerated ray tracing found in the new Volta-generation GPUs.
