1rtcSetGeometryPointQueryFuEnmcbtrieoen(R3a)y TracingrKtecrSneetlGseo3metryPointQueryFunction(3)
2 NAME
6 rtcSetGeometryPointQueryFunction - sets the point query callback function
7 for a geometry
8 SYNOPSIS
10 #include <embree3/rtcore.h>
11 struct RTCPointQueryFunctionArguments
13 {
14 // the (world space) query object that was passed as an argument of rtcPointQuery.
15 struct RTCPointQuery* query;
16 // used for user input/output data. Will not be read or modified internally.
18 void* userPtr;
19 // primitive and geometry ID of primitive
21 unsigned int primID;
22 unsigned int geomID;
23 // the instance stack with instance IDs and transformation information
25 struct RTCPointQueryInstanceStack* instStack;
26 // scaling factor indicating whether the current instance transformation
28 // is a similarity transformation.
29 float similarityScale;
30 };
31 typedef bool (*RTCPointQueryFunction)(
33 struct RTCPointQueryFunctionArguments* args
34 );
35 void rtcSetGeometryPointQueryFunction(
37 RTCGeometry geometry,
38 RTCPointQueryFunction queryFunc
39 );
40 DESCRIPTION
42 The rtcSetGeometryPointQueryFunction function registers a point query
43 callback function (queryFunc argument) for the specified geometry
44 (geometry argument).
45 Only a single callback function can be registered per geometry and fur‐
47 ther invocations overwrite the previously set callback function. Pass‐
48 ing NULL as function pointer disables the registered callback function.
49 The registered callback function is invoked by [rtcPointQuery] for
51 every primitive of the geometry that intersects the corresponding point
52 query domain. The callback function of type RTCPointQueryFunction gets
53 passed a number of arguments through the RTCPointQueryFunctionArguments
54 structure. The query object is the original point query object passed
55 into [rtcPointQuery], usrPtr is an arbitrary pointer to pass input into
56 and store results of the callback function. The primID, geomID and
57 instStack (see [rtcInitPointQueryInstanceStack] for details) can be
58 used to identify the geometry data of the primitive.
59 A RTCPointQueryFunction can also be passed directly as an argument to
61 [rtcPointQuery]. In this case the callback is invoked for all primi‐
62 tives in the scene that intersect the query domain. If a callback
63 function is passed as an argument to [rtcPointQuery] and (a potentially
64 different) callback function is set for a geometry with [rtcSetGeome‐
65 tryPointQueryFunction] both callback functions are invoked.
66 If instancing is used, the parameter simliarityScale indicates whether
68 the current instance transform (top element of instStack) is a similar‐
69 ity transformation or not. Similarity transformations are composed of
70 translation, rotation and uniform scaling and if a matrix M defines a
71 similarity transformation, there is a scaling factor D such that for
72 all x,y: dist(Mx, My) = D * dist(x, y). In this case the parameter
73 scalingFactor is this scaling factor D and otherwise it is 0. A valid
74 similarity scale (similarityScale > 0) allows to compute distance
75 information in instance space and scale the distances accordingly into
76 world space (for example, to update the query radius, see below). If
77 the current instance transform is not a similarity transform (similari‐
78 tyScale is 0), the distance computation has to be performed in world
79 space to ensure correctness. In this case the instance to world trans‐
80 formations given with the instStack should be used to transform the
81 primitive data into world space. Otherwise, the query location can be
82 transformed into instance space which can be more efficient. If there
83 is no instance transform, the similarity scale is 1.
84 The callback function will potentially be called for primitives outside
86 the query domain for two resons: First, the callback is invoked for all
87 primitives inside a BVH leaf node since no geometry data of primitives
88 is determined internally and therefore individual primitives are not
89 culled (only their (aggregated) bounding boxes). Second, in case non
90 similarity transformations are used, the resulting ellipsoidal query
91 domain (in instance space) is approximated by its axis aligned bounding
92 box internally and therefore inner nodes that do not intersect the
93 original domain might intersect the approximative bounding box which
94 results in unneccessary callbacks. In any case, the callbacks are con‐
95 servative, i.e. if a primitive is inside the query domain a callback
96 will be invoked but the reverse is not neccessarily true.
97 For efficiency, the radius of the query object can be decreased (in
99 world space) inside the callback function to improve culling of geome‐
100 try during BVH traversal. If the query radius was updated, the call‐
101 back function should return true to issue an update of internal traver‐
102 sal information. Increasing the radius or modifying the time or posi‐
103 tion of the query results in undefined behaviour.
104 Within the callback function, it is safe to call [rtcPointQuery] again,
106 for example when implementing instancing manually. In this case the
107 instance transformation should be pushed onto the instStack. Embree
108 will internally compute the point query information in instance space
109 using the top element of instStack when [rtcPointQuery] is called.
110 For a reference implementation of a closest point traversal of triangle
112 meshes using instancing and user defined instancing see the tutorial
113 [ClosestPoint].
114 SEE ALSO
116 [rtcPointQuery], [rtcInitPointQueryInstanceStack]
117 rtcSetGeometryPointQueryFunction(3)