Manpages - rtcSetGeometryPointQueryFunction.3embree3

  rtcSetGeometryPointQueryFunction - sets the point query callback function
    for a geometry

  #include <embree3/rtcore.h>

  struct RTCPointQueryFunctionArguments
  {
    // the (world space) query object that was passed as an argument of rtcPointQuery.
    struct RTCPointQuery* query;

    // used for user input/output data. Will not be read or modified internally.
    void* userPtr;

    // primitive and geometry ID of primitive
    unsigned int  primID;        
    unsigned int  geomID;    

    // the context with transformation and instance ID stack
    struct RTCPointQueryContext* context;

    // scaling factor indicating whether the current instance transformation
    // is a similarity transformation.
    float similarityScale;
  };

  typedef bool (*RTCPointQueryFunction)(
    struct RTCPointQueryFunctionArguments* args
  );

  void rtcSetGeometryPointQueryFunction(
    RTCGeometry geometry,
    RTCPointQueryFunction queryFunc
  );

The rtcSetGeometryPointQueryFunction function registers a point query callback function (queryFunc argument) for the specified 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 [rtcPointQuery] for every primitive of the geometry that intersects the corresponding point query domain. The callback function of type RTCPointQueryFunction gets passed a number of arguments through the RTCPointQueryFunctionArguments structure. The query object is the original point query object passed into [rtcPointQuery], usrPtr is an arbitrary pointer to pass input into and store results of the callback function. The primID, geomID and context (see [rtcInitPointQueryContext] for details) can be used to identify the geometry data of the primitive.

A RTCPointQueryFunction can also be passed directly as an argument to [rtcPointQuery]. In this case the callback is invoked for all primitives in the scene that intersect the query domain. If a callback function is passed as an argument to [rtcPointQuery] and (a potentially different) callback function is set for a geometry with [rtcSetGeometryPointQueryFunction] both callback functions are invoked and the callback function passed to [rtcPointQuery] will be called before the geometry specific callback function.

If instancing is used, the parameter simliarityScale indicates whether the current instance transform (top element of the stack in context) is a similarity transformation or not. Similarity transformations are composed of translation, rotation and uniform scaling and if a matrix M defines a similarity transformation, there is a scaling factor D such that for all x,y: dist(Mx, My) = D * dist(x, y). In this case the parameter scalingFactor is this scaling factor D and otherwise it is 0. A valid similarity scale (similarityScale > 0) allows to compute distance information in instance space and scale the distances into world space (for example, to update the query radius, see below) by dividing the instance space distance with the similarity scale. If the current instance transform is not a similarity transform (similarityScale is 0), the distance computation has to be performed in world space to ensure correctness. In this case the instance to world transformations given with the context should be used to transform the primitive data into world space. Otherwise, the query location can be transformed into instance space which can be more efficient. If there is no instance transform, the similarity scale is 1.

The callback function will potentially be called for primitives outside the query domain for two resons: First, the callback is invoked for all primitives inside a BVH leaf node since no geometry data of primitives is determined internally and therefore individual primitives are not culled (only their (aggregated) bounding boxes). Second, in case non similarity transformations are used, the resulting ellipsoidal query domain (in instance space) is approximated by its axis aligned bounding box internally and therefore inner nodes that do not intersect the original domain might intersect the approximative bounding box which results in unneccessary callbacks. In any case, the callbacks are conservative, i.e. if a primitive is inside the query domain a callback will be invoked but the reverse is not neccessarily true.

For efficiency, the radius of the query object can be decreased (in world space) inside the callback function to improve culling of geometry during BVH traversal. If the query radius was updated, the callback function should return true to issue an update of internal traversal information. Increasing the radius or modifying the time or position of the query results in undefined behaviour.

Within the callback function, it is safe to call [rtcPointQuery] again, for example when implementing instancing manually. In this case the instance transformation should be pushed onto the stack in context. Embree will internally compute the point query information in instance space using the top element of the stack in context when [rtcPointQuery] is called.

For a reference implementation of a closest point traversal of triangle meshes using instancing and user defined instancing see the tutorial [ClosestPoint].

[rtcPointQuery], [rtcInitPointQueryContext]