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|RTC_GEOMETRY_TYPE_INSTANCE(3)||Embree Ray Tracing Kernels 3||RTC_GEOMETRY_TYPE_INSTANCE(3)|
RTC_GEOMETRY_TYPE_INSTANCE - instance geometry type
#include <embree3/rtcore.h> RTCGeometry geometry = rtcNewGeometry(device, RTC_GEOMETRY_TYPE_INSTANCE);
DESCRIPTION¶Embree supports instancing of scenes using affine transformations (3×3 matrix plus translation). As the instanced scene is stored only a single time, even if instanced to multiple locations, this feature can be used to create very complex scenes with small memory footprint.
Embree supports both single-level instancing and multi-level instancing. The maximum instance nesting depth is RTC_MAX_INSTANCE_LEVEL_COUNT; it can be configured at compile-time using the constant EMBREE_MAX_INSTANCE_LEVEL_COUNT. Users should adapt this constant to their needs: instances nested any deeper are silently ignored in release mode, and cause assertions in debug mode.
Instances are created by passing RTC_GEOMETRY_TYPE_INSTANCE to the rtcNewGeometry function call. The instanced scene can be set using the rtcSetGeometryInstancedScene call, and the affine transformation can be set using the rtcSetGeometryTransform function.
Please note that rtcCommitScene on the instanced scene should be called first, followed by rtcCommitGeometry on the instance, followed by rtcCommitScene for the top-level scene containing the instance.
If a ray hits the instance, the geomID and primID members of the hit are set to the geometry ID and primitive ID of the hit primitive in the instanced scene, and the instID member of the hit is set to the geometry ID of the instance in the top-level scene.
The instancing scheme can also be implemented using user geometries. To achieve this, the user geometry code should set the instID member of the intersection context to the geometry ID of the instance, then trace the transformed ray, and finally set the instID field of the intersection context again to -1. The instID field is copied automatically by each primitive intersector into the instID field of the hit structure when the primitive is hit. See the [User Geometry] tutorial for an example.
For multi-segment motion blur, the number of time steps must be first specified using the rtcSetGeometryTimeStepCount function. Then a transformation for each time step can be specified using the rtcSetGeometryTransform function.
See tutorials [Instanced Geometry] and [Multi Level Instancing] for examples of how to use instances.