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Intel® Embree

High Performance Ray Tracing Kernels

We recently released Intel® Embree v3.6.1!

Embree Tutorials

Embree comes with a set of tutorials aimed at helping users understand how Embree can be used and extended. There is a very basic minimal that can be compiled as both C and C++, which should get new users started quickly. All other tutorials exist in an ISPC and C++ version to demonstrate the two versions of the API. Look for files named tutorialname_device.ispc for the ISPC implementation of the tutorial, and files named tutorialname_device.cpp for the single ray C++ version of the tutorial. To start the C++ version use the tutorialname executables, to start the ISPC version use the tutorialname_ispc executables. All tutorials can print available command line options using the --help command line parameter.

For all tutorials except minimal, you can select an initial camera using the --vp (camera position), --vi (camera look-at point), --vu (camera up vector), and --fov (vertical field of view) command line parameters:

./triangle_geometry --vp 10 10 10 --vi 0 0 0

You can select the initial window size using the --size command line parameter, or start the tutorials in full screen using the --fullscreen parameter:

./triangle_geometry --size 1024 1024
./triangle_geometry --fullscreen

The initialization string for the Embree device (rtcNewDevice call) can be passed to the ray tracing core through the --rtcore command line parameter, e.g.:

./triangle_geometry --rtcore verbose=2,threads=1

The navigation in the interactive display mode follows the camera orbit model, where the camera revolves around the current center of interest. With the left mouse button you can rotate around the center of interest (the point initially set with --vi). Holding Control pressed while clicking the left mouse button rotates the camera around its location. You can also use the arrow keys for navigation.

You can use the following keys:

F1
Default shading
F2
Gray EyeLight shading
F3
Traces occlusion rays only.
F4
UV Coordinate visualization
F5
Geometry normal visualization
F6
Geometry ID visualization
F7
Geometry ID and Primitive ID visualization
F8
Simple shading with 16 rays per pixel for benchmarking.
F9
Switches to render cost visualization. Pressing again reduces brightness.
F10
Switches to render cost visualization. Pressing again increases brightness.
f
Enters or leaves full screen mode.
c
Prints camera parameters.
ESC
Exits the tutorial.
q
Exits the tutorial.

Minimal

This tutorial is designed to get new users started with Embree. It can be compiled as both C and C++. It demonstrates how to initialize a device and scene, and how to intersect rays with the scene. There is no image output to keep the tutorial as simple as possible.

Triangle Geometry

This tutorial demonstrates the creation of a static cube and ground plane using triangle meshes. It also demonstrates the use of the rtcIntersect1 and rtcOccluded1 functions to render primary visibility and hard shadows. The cube sides are colored based on the ID of the hit primitive.

Dynamic Scene

This tutorial demonstrates the creation of a dynamic scene, consisting of several deforming spheres. Half of the spheres use the RTC_BUILD_QUALITY_REFIT geometry build quality, which allows Embree to use a refitting strategy for these spheres, the other half uses the RTC_BUILD_QUALITY_LOW geometry build quality, causing a high performance rebuild of their spatial data structure each frame. The spheres are colored based on the ID of the hit sphere geometry.

User Geometry

This tutorial shows the use of user-defined geometry, to re-implement instancing, and to add analytic spheres. A two-level scene is created, with a triangle mesh as ground plane, and several user geometries that instance other scenes with a small number of spheres of different kinds. The spheres are colored using the instance ID and geometry ID of the hit sphere, to demonstrate how the same geometry instanced in different ways can be distinguished.

Viewer

This tutorial demonstrates a simple OBJ viewer that traces primary visibility rays only. A scene consisting of multiple meshes is created, each mesh sharing the index and vertex buffer with the application. It also demonstrates how to support additional per-vertex data, such as shading normals.

You need to specify an OBJ file at the command line for this tutorial to work:

./viewer -i model.obj

Stream Viewer

This tutorial is a simple OBJ viewer that demonstrates the use of ray streams. You need to specify an OBJ file at the command line for this tutorial to work:

./viewer_stream -i model.obj

Intersection Filter

This tutorial demonstrates the use of filter callback functions to efficiently implement transparent objects. The filter function used for primary rays lets the ray pass through the geometry if it is entirely transparent. Otherwise, the shading loop handles the transparency properly, by potentially shooting secondary rays. The filter function used for shadow rays accumulates the transparency of all surfaces along the ray, and terminates traversal if an opaque occluder is hit.

Instanced Geometry

This tutorial demonstrates the in-build instancing feature of Embree, by instancing a number of other scenes built from triangulated spheres. The spheres are again colored using the instance ID and geometry ID of the hit sphere, to demonstrate how the same geometry instanced in different ways can be distinguished.

Multi Level Instancing

This tutorial demonstrates multi-level instancing, i.e., nesting instances into instances. To enable the tutorial, set the compile-time variable EMBREE_MAX_INSTANCE_LEVEL_COUNT to a value other than the default 1. This variable is available in the code as RTC_MAX_INSTANCE_LEVEL_COUNT.

The renderer uses a basic path tracing approach, and the image will progressively refine over time. There are two levels of instances in this scene: multiple instances of the same tree nest instances of a twig. Intersections on up to RTC_MAX_INSTANCE_LEVEL_COUNT nested levels of instances work out of the box. Users may obtain the instance ID stack for a given hitpoint from the instID member. During shading, the instance ID stack is used to accumulate normal transformation matrices for each hit. The tutorial visualizes transformed normals as colors.

Path Tracer

This tutorial is a simple path tracer, based on the viewer tutorial.

You need to specify an OBJ file and light source at the command line for this tutorial to work:

./pathtracer -i model.obj --ambientlight 1 1 1

As example models we provide the "Austrian Imperial Crown" model by Martin Lubich and the "Asian Dragon" model from the Stanford 3D Scanning Repository.

crown.zip

asian_dragon.zip

To render these models execute the following:

./pathtracer -c crown/crown.ecs
./pathtracer -c asian_dragon/asian_dragon.ecs

Hair

This tutorial demonstrates the use of the hair geometry to render a hairball.

Curve Geometry

This tutorial demonstrates the use of the B-Spline and Catmull-Rom curve geometries.

Subdivision Geometry

This tutorial demonstrates the use of Catmull-Clark subdivision surfaces.

Displacement Geometry

This tutorial demonstrates the use of Catmull-Clark subdivision surfaces with procedural displacement mapping using a constant edge tessellation level.

Grid Geometry

This tutorial demonstrates the use of the memory efficient grid primitive to handle highly tessellated and displaced geometry.

Point Geometry

This tutorial demonstrates the use of the three representations of point geometry.

Motion Blur Geometry

This tutorial demonstrates rendering of motion blur using the multi-segment motion blur feature. Shown is motion blur of a triangle mesh, quad mesh, subdivision surface, line segments, hair geometry, Bézier curves, instantiated triangle mesh where the instance moves, instantiated quad mesh where the instance and the quads move, and user geometry.

The number of time steps used can be configured using the --time-steps <int> and --time-steps2 <int> command line parameters, and the geometry can be rendered at a specific time using the the --time <float> command line parameter.

Interpolation

This tutorial demonstrates interpolation of user-defined per-vertex data.

Closest Point

This tutorial demonstrates a use-case of the point query API. The scene consists of a simple collection of objects that are instanced and for several point in the scene (red points) the closest point on the surfaces of the scene are computed (white points). The closest point functionality is implemented for Embree internal and for user-defined instancing. The tutorial also illustrates how to handle instance transformations that are not similarity transforms.

Voronoi

This tutorial demonstrates how to implement nearest neighbour lookups using the point query API. Several colored points are located on a plane and the corresponding voroni regions are illustrated.

BVH Builder

This tutorial demonstrates how to use the templated hierarchy builders of Embree to build a bounding volume hierarchy with a user-defined memory layout using a high-quality SAH builder using spatial splits, a standard SAH builder, and a very fast Morton builder.

BVH Access

This tutorial demonstrates how to access the internal triangle acceleration structure build by Embree. Please be aware that the internal Embree data structures might change between Embree updates.

Find Embree

This tutorial demonstrates how to use the FIND_PACKAGE CMake feature to use an installed Embree. Under Linux and macOS the tutorial finds the Embree installation automatically, under Windows the embree_DIR CMake variable must be set to the following folder of the Embree installation: C:\Program Files\Intel\Embree3.