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02_scene_intersection.md

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02_scene_intersection


This demo illustrates the usage of the hiprtScene object in the HIPRT API, focusing on creating, building, and using a scene for ray tracing.
The triangle mesh is the basic primitive of HIPRT from which we build hiprtGeometry. In general, scenes are comprised of many meshes. Developers can utilize hiprtScene support on top of these meshes to create an acceleration structure which can be used to search for a mesh efficiently when there are many meshes.

img

The geometry setup of this demo is close to the previous demo. We are just creating 2 triangles instead of 1.



The difference compared to the previous demo is that we use hiprtScene. First, we need to set the sceneInput that will be used to create and build the hiprtScene. An instance of the geometry is created and added to the scene. The sceneInput is configured with this instance, and transformation parameters are set:

  hiprtInstance instance;
  instance.type    = hiprtInstanceTypeGeometry;
  instance.geometry = geom;

  hiprtSceneBuildInput sceneInput;
  sceneInput.instanceCount      = 1;
  sceneInput.instanceMasks      = nullptr;
  sceneInput.instanceTransformHeaders = nullptr;
  oroMalloc( reinterpret_cast<oroDeviceptr*>( &sceneInput.instances ), sizeof( hiprtInstance ) );
  oroMemcpyHtoD( reinterpret_cast<oroDeviceptr>( sceneInput.instances ), &instance, sizeof( hiprtInstance ) );

  hiprtFrameSRT frame;
  frame.translation    = make_hiprtFloat3( 0.0f, 0.0f, 0.0f );
  frame.scale        = make_hiprtFloat3( 0.5f, 0.5f, 0.5f );
  frame.rotation      = make_hiprtFloat4( 0.0f, 0.0f, 1.0f, 0.0f );
  sceneInput.frameCount = 1;
  oroMalloc( reinterpret_cast<oroDeviceptr*>( &sceneInput.instanceFrames ), sizeof( hiprtFrameSRT ) );
  oroMemcpyHtoD( reinterpret_cast<oroDeviceptr>( sceneInput.instanceFrames ), &frame, sizeof( hiprtFrameSRT ) );

If there are more meshes in a scene, we need to create many geometries.



The scene is built using HIPRT functions. Note that we need to create a temporary buffer. Temporary buffers are intermediate memory allocations used during the construction of the geometry and scene in HIPRT. These buffers are necessary for storing intermediate data required by the HIPRT API to build complex structures, such as BVHs or other acceleration structures, but are not needed once the build process is complete. Therefore, we can release it after the build.

  size_t       sceneTempSize;
  hiprtDevicePtr sceneTemp = nullptr;
  hiprtGetSceneBuildTemporaryBufferSize( ctxt, sceneInput, options, sceneTempSize );
  oroMalloc( reinterpret_cast<oroDeviceptr*>( &sceneTemp ), sceneTempSize );

  hiprtScene scene = nullptr;
  hiprtCreateScene( ctxt, sceneInput, options, scene );
  hiprtBuildScene( ctxt, hiprtBuildOperationBuild, sceneInput, options, sceneTemp, 0, scene );

  // we can free the Temporary Buffer just after hiprtBuildScene, as this buffer is only used during the build.
  oroFree( reinterpret_cast<oroDeviceptr>( sceneTemp ) );
  sceneTemp = nullptr;


Concerning the kernel it is also close to the previous demo, but instead of manipulating hiprtGeometry, it uses hiprtScene.
so, hiprtGeometry is replaced by hiprtScene, and hiprtGeomTraversalClosest is replaced by hiprtSceneTraversalClosest.