Ray-tracing hardware is special-purpose computer hardware designed for accelerating ray tracing calculations.
The problem of rendering 3D graphics can be conceptually presented as finding all intersections between a set of "primitives" (typically triangles or polygons) and a set of "rays" (typically one or more per pixel). [1]
Up to 2010, all typical graphic acceleration boards, called graphics processing units (GPUs), used 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. [a] 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 [2] nearly impossible to compute.
The ray tracing algorithm is inherently suitable for scaling by parallelization of individual ray renders. [3] However, anything other than ray casting requires recursion of the ray tracing algorithm (and random access to the scene graph) to complete their analysis, [4] 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. [b]
The complexity of a well implemented ray tracing algorithm scales logarithmically; [c] this is due to objects (triangles and collections of triangles) 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. [5] [d]
Various implementations of ray tracing hardware have been created, both experimental and commercial:
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