Ray Tracing Contexts

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'Modern Hall, at dusk', based on a model by NewSee2l035

Nearly all physically based rendering algorithms necessitate to perform ray tracing queries against some geometry. In Fermat this happens through a ray tracing context, which provides the following interface:

// A class defining core ray tracing functionality, ranging from geometry setup to
// performing actual ray tracing queries.
//
struct RTContext
{
   // create a ray tracing context on the given triangle mesh
   //
   void create_geometry(
       const uint32    tri_count,
       const int*      index_ptr,
       const uint32    vertex_count,
       const float*    vertex_ptr,
       const int*      normal_index_ptr,
       const float*    normal_vertex_ptr,
       const int*      tex_index_ptr,
       const float*    tex_vertex_ptr,
       const int*      material_index_ptr);

   // trace a set of rays, returning a full hit
   //
   void trace(const uint32 count, const Ray* rays, Hit* hits);

   // trace a set of masked rays, returning a full hit
   //
   void trace(const uint32 count, const MaskedRay* rays, Hit* hits);

   // trace a set of masked shadow rays, returning a full primitive hit
   //
   void trace_shadow(const uint32 count, const MaskedRay* rays, Hit* hits);

   // trace a set of masked shadow rays, returning a single bool hit|no hit bit for each ray
   //
   void trace_shadow(const uint32 count, const MaskedRay* rays, uint32* binary_hits);
};

Notice how there are two types of rays that can be traced: Ray and MaskedRay. The first is specified by an origin, a direction, and a full [tmin, tmax] range specifying valid intersection distances.
The second is specified by an origin, a direction, a mask, and a single maximum intersection distance, tmax. The mask is used to allow masking out geometry at ray tracing time: the ray's mask is OR'ed against the triangles masks, and triangles which result in a non-zero mask get discarded.
The other difference is in the type of tracing queries that can be performed: regular trace() queries return the closest hit among all geometries, while trace_shadow() queries may return upon the first hit encountered during the traversal process, in practice simply answering the question: "is the given ray segment shadowed?".

Next: The Rendering Context