rtcBuildBVH(3)

  NAME

        rtcBuildBVH - builds a BVH

  SYNOPSIS

        #include <embree4/rtcore.h>

        struct RTC_ALIGN(32) RTCBuildPrimitive
        {
          float lower_x, lower_y, lower_z;
          unsigned int geomID;
          float upper_x, upper_y, upper_z;
          unsigned int primID;
        };

        typedef void* (*RTCCreateNodeFunction) (
          RTCThreadLocalAllocator allocator,
          unsigned int childCount,
          void* userPtr
        );

        typedef void (*RTCSetNodeChildrenFunction) (
          void* nodePtr,
          void** children,
          unsigned int childCount,
          void* userPtr
        );

        typedef void (*RTCSetNodeBoundsFunction) (
          void* nodePtr,
          const struct RTCBounds** bounds,
          unsigned int childCount,
          void* userPtr
        );

        typedef void* (*RTCCreateLeafFunction) (
          RTCThreadLocalAllocator allocator,
          const struct RTCBuildPrimitive* primitives,
          size_t primitiveCount,
          void* userPtr
        );

        typedef void (*RTCSplitPrimitiveFunction) (
          const struct RTCBuildPrimitive* primitive,
          unsigned int dimension,
          float position,
          struct RTCBounds* leftBounds,
          struct RTCBounds* rightBounds,
          void* userPtr
        );

        typedef bool (*RTCProgressMonitorFunction)(
          void* userPtr, double n
        );

        enum RTCBuildFlags
        {
          RTC_BUILD_FLAG_NONE,
          RTC_BUILD_FLAG_DYNAMIC
        };

        struct RTCBuildArguments
        {
          size_t byteSize;

          enum RTCBuildQuality buildQuality;
          enum RTCBuildFlags buildFlags;
          unsigned int maxBranchingFactor;
          unsigned int maxDepth;
          unsigned int sahBlockSize;
          unsigned int minLeafSize;
          unsigned int maxLeafSize;
          float traversalCost;
          float intersectionCost;

          RTCBVH bvh;
          struct RTCBuildPrimitive* primitives;
          size_t primitiveCount;
          size_t primitiveArrayCapacity;

          RTCCreateNodeFunction createNode;
          RTCSetNodeChildrenFunction setNodeChildren;
          RTCSetNodeBoundsFunction setNodeBounds;
          RTCCreateLeafFunction createLeaf;
          RTCSplitPrimitiveFunction splitPrimitive;
          RTCProgressMonitorFunction buildProgress;
          void* userPtr;
        };

        struct RTCBuildArguments rtcDefaultBuildArguments();

        void* rtcBuildBVH(
          const struct RTCBuildArguments* args
        );

  DESCRIPTION
The rtcBuildBVH function can be used to build a BVH in a user-defined format over arbitrary primitives. All arguments to the function are provided through the RTCBuildArguments structure. The first member of that structure must be set to the size of the structure in bytes (bytesSize member) which allows future extensions of the structure. It is recommended to initialize the build arguments structure using the rtcDefaultBuildArguments function.

The rtcBuildBVH function gets passed the BVH to build (bvh member), the array of primitives (primitives member), the capacity of that array (primitiveArrayCapacity member), the number of primitives stored inside the array (primitiveCount member), callback function pointers, and a user-defined pointer (userPtr member) that is passed to all callback functions when invoked. The primitives array can be freed by the application after the BVH is built. All callback functions are typically called from multiple threads, thus their implementation must be thread-safe.

Four callback functions must be registered, which are invoked during build to create BVH nodes (createNode member), to set the pointers to all children (setNodeChildren member), to set the bounding boxes of all children (setNodeBounds member), and to create a leaf node (createLeaf member).

The function pointer to the primitive split function (splitPrimitive member) may be NULL, however, then no spatial splitting in high quality mode is possible. The function pointer used to report the build progress (buildProgress member) is optional and may also be NULL.

Further, some build settings are passed to configure the BVH build. Using the build quality settings (buildQuality member), one can select between a faster, low quality build which is good for dynamic scenes, and a standard quality build for static scenes. One can also specify the desired maximum branching factor of the BVH (maxBranchingFactor member), the maximum depth the BVH should have (maxDepth member), the block size for the SAH heuristic (sahBlockSize member), the minimum and maximum leaf size (minLeafSize and maxLeafSize member), and the estimated costs of one traversal step and one primitive intersection (traversalCost and intersectionCost members). When enabling the RTC_BUILD_FLAG_DYNAMIC build flags (buildFlags member), re-build performance for dynamic scenes is improved at the cost of higher memory requirements.

To spatially split primitives in high quality mode, the builder needs extra space at the end of the build primitive array to store split primitives. The total capacity of the build primitive array is passed using the primitiveArrayCapacity member, and should be about twice the number of primitives when using spatial splits.

The RTCCreateNodeFunc and RTCCreateLeafFunc callbacks are passed a thread local allocator object that should be used for fast allocation of nodes using the rtcThreadLocalAlloc function. We strongly recommend using this allocation mechanism, as alternative approaches like standard malloc can be over 10× slower. The allocator object passed to the create callbacks may be used only inside the current thread. Memory allocated using rtcThreadLocalAlloc is automatically freed when the RTCBVH object is deleted. If you use your own memory allocation scheme you have to free the memory yourself when the RTCBVH object is no longer used.

The RTCCreateNodeFunc callback additionally gets the number of children for this node in the range from 2 to maxBranchingFactor (childCount argument).

The RTCSetNodeChildFunc callback function gets a pointer to the node as input (nodePtr argument), an array of pointers to the children (childPtrs argument), and the size of this array (childCount argument).

The RTCSetNodeBoundsFunc callback function gets a pointer to the node as input (nodePtr argument), an array of pointers to the bounding boxes of the children (bounds argument), and the size of this array (childCount argument).

The RTCCreateLeafFunc callback additionally gets an array of primitives as input (primitives argument), and the size of this array (primitiveCount argument). The callback should read the geomID and primID members from the passed primitives to construct the leaf.

The RTCSplitPrimitiveFunc callback is invoked in high quality mode to split a primitive (primitive argument) at the specified position (position argument) and dimension (dimension argument). The callback should return bounds of the clipped left and right parts of the primitive (leftBounds and rightBounds arguments).

The RTCProgressMonitorFunction callback function is called with the estimated completion rate n in the range [0, 1]. Returning true from the callback lets the build continue; returning false cancels the build.

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

  SEE ALSO
[rtcNewBVH]