rtcSetGeometryIntersectFunction - sets the callback function to
  intersect a user geometry


#include <embree3/rtcore.h>

struct RTCIntersectFunctionNArguments
  int* valid;
  void* geometryUserPtr;
  unsigned int primID;
  struct RTCIntersectContext* context;
  struct RTCRayHitN* rayhit;
  unsigned int N;
  unsigned int geomID;

typedef void (*RTCIntersectFunctionN)(
  const struct RTCIntersectFunctionNArguments* args

void rtcSetGeometryIntersectFunction(
  RTCGeometry geometry,
  RTCIntersectFunctionN intersect


The rtcSetGeometryIntersectFunction function registers a ray/primitive intersection callback function (intersect argument) for the specified user geometry (geometry argument).

Only a single callback function can be registered per geometry and further invocations overwrite the previously set callback function. Passing NULL as function pointer disables the registered callback function.

The registered callback function is invoked by rtcIntersect-type ray queries to calculate the intersection of a ray packet of variable size with one user-defined primitive. The callback function of type RTCIntersectFunctionN gets passed a number of arguments through the RTCIntersectFunctionNArguments structure. The value N specifies the ray packet size, valid points to an array of integers that specify whether the corresponding ray is valid (-1) or invalid (0), the geometryUserPtr member points to the geometry user data previously set through rtcSetGeometryUserData, the context member points to the intersection context passed to the ray query, the rayhit member points to a ray and hit packet of variable size N, and the geomID and primID member identifies the geometry ID and primitive ID of the primitive to intersect.

The ray component of the rayhit structure contains valid data, in particular the tfar value is the current closest hit distance found. All data inside the hit component of the rayhit structure are undefined and should not be read by the function.

The task of the callback function is to intersect each active ray from the ray packet with the specified user primitive. If the user-defined primitive is missed by a ray of the ray packet, the function should return without modifying the ray or hit. If an intersection of the user-defined primitive with the ray was found in the valid range (from tnear to tfar), it should update the hit distance of the ray (tfar member) and the hit (u, v, Ng, instID, geomID, primID members). In particular, the currently intersected instance is stored in the instID field of the intersection context, which must be deep copied into the instID member of the hit.

As a primitive might have multiple intersections with a ray, the intersection filter function needs to be invoked by the user geometry intersection callback for each encountered intersection, if filtering of intersections is desired. This can be achieved through the rtcFilterIntersection call.

Within the user geometry intersect function, it is safe to trace new rays and create new scenes and geometries.


On failure an error code is set that can be queried using rtcGetDeviceError.


[rtcSetGeometryOccludedFunction], [rtcSetGeometryUserData], [rtcFilterIntersection]


Embree Ray Tracing Kernels 3