NanoRT, single header only modern ray tracing kernel.

Path tracing example contributed by https://github.com/daseyb

NanoRT is simple single header only ray tracing kernel.

Features

• Portable C++
  • Only use C++-03 features by default.
  • C++11 feature(threads) is also available
  • There is experimental C89 port of NanoRT in c89 branch https://github.com/lighttransport/nanort/tree/c89
• BVH spatial data structure for efficient ray intersection finding.
  • Should be able to handle ~10M triangles scene efficiently with moderate memory consumption
• Custom geometry & intersection
  • Built-in triangle mesh gemetry & intersector is provided.
• Cross platform
  • MacOSX, Linux, Windows, iOS, Android, ARM, x86, SPARC, (maybe) MIPS, (will be) RISC-V, etc.
  • For example, NanoRT works finely on Raspberry Pi 2 (arm 32bit) and Raspberrry Pi 3!(AARCH64 kernel)
• GPU efficient data structure
  • Built BVH tree from NanoRT is a linear array and does not have pointers, thus it is suited for GPU raytracing (GPU ray traversal).
• OpenMP multithreaded BVH build.
• Robust intersection calculation.
  • Robust BVH Ray Traversal (using up to 4 ulp version): http://jcgt.org/published/0002/02/02/
  • Watertight Ray/Triangle Intesection: http://jcgt.org/published/0002/01/05/
• Double precision support
  • Beneficial for HPC and scientific visualization.

Applications

• Test renderer for your light transport algorithm development.
• Test renderer for your shader language development.
• Collision detection (ray casting).
• BVH builder for GPU/Accelerator ray traversal.
• Add 2D/3D rendering feature for non-GPU system.
  • [ ] ImGui backend? https://github.com/syoyo/imgui/tree/nanort
  • [ ] Nano SVG backend? https://github.com/syoyo/nanovg-nanort

Projects using NanoRT

• lightmetrica https://github.com/hi2p-perim/lightmetrica-v2
• OSPRay NanoRT module https://github.com/jeffamstutz/module_nanort/
• Your project here!

Projects similar/related to NanoRT

• bvh: C++17 BVH Construction and Traversal Library https://github.com/madmann91/bvh
• BlazeRT: double precision ray tracer for scientific or engineering applications https://github.com/cstatz/blazert

API

nanort::Ray represents ray. The origin org, the direction dir (not necessarily normalized), the minimum hit distance min_t(usually 0.0) and the maximum hit distance max_t (usually too far, e.g. 1.0e+30) must be filled before shooting ray.

nanort::BVHAccel builds BVH data structure from geometry, and provides the function to find intersection point for a given ray.

nanort::BVHBuildOptions specifies parameters for BVH build. Usually default parameters should work well.

nanort::BVHTraceOptions specifies ray traverse/intersection options.

template<typename T>
class {
  T org[3];        // [in] must set
  T dir[3];        // [in] must set
  T min_t;         // [in] must set
  T max_t;         // [in] must set
  unsigned int type;  // optional. ray type.
} Ray;

class BVHTraceOptions {
  // Trace rays only in face ids range. faceIdsRange[0] < faceIdsRange[1]
  // default: 0 to 0x3FFFFFFF(2G faces)
  unsigned int prim_ids_range[2];
  bool cull_back_face; // default: false
};

nanort::BVHBuildOptions<float> build_options; // BVH build option(optional)

const float *vertices = ...;
const unsigned int *faces = ...;

// Need to specify stride bytes for `vertices`.
// When vertex is stored XYZXYZXYZ... in float type, stride become 12(= sizeof(float) * 3).
nanort::TriangleMesh<float> triangle_mesh(vertices, faces, /* stride */sizeof(float) * 3);
nanort::TriangleSAHPred<float> triangle_pred(vertices, faces, /* stride */sizeof(float) * 3);

nanort::BVHAccel<float> accel;
ret = accel.Build(mesh.num_faces, triangle_mesh, triangle_pred, build_options);

nanort::TriangleIntersector<> triangle_intersecter(vertices, faces, /* stride */sizeof(float) * 3);

nanort::Ray<float> ray;
// fill ray org and ray dir.
...
// fill minimum and maximum hit distance.
ray.min_t = 0.0f;
ray.max_t = 1.0e+30f;

nanort::TriangleIntersection<float> isect;

// Store nearest hit point to `isect` and returns true if the hit point found.
BVHTraceOptions trace_options; // optional
bool hit = accel.Traverse(ray, triangle_intersecter, &isect, trace_options);

Application must prepare geometric information and store it in linear array.

For a builtin Triangle intersector,

• vertices : The array of triangle vertices (e.g. xyz * numVertices)
• faces : The array of triangle face indices (3 * numFaces)
• stride : Byte stride of each vertex data

are required attributes.

Usage

// NanoRT defines template based class, so no NANORT_IMPLEMENTATION anymore.
#include "nanort.h"
Mesh mesh;
// load mesh data...
nanort::BVHBuildOptions<float> options; // Use default option
nanort::TriangleMesh<float> triangle_mesh(mesh.vertices, mesh.faces, /* stride */sizeof(float) * 3);
nanort::TriangleSAHPred<float> triangle_pred(mesh.vertices, mesh.faces, /* stride */sizeof(float) * 3);
nanort::BVHAccel<float> accel;
ret = accel.Build(mesh.vertices, mesh.faces, mesh.num_faces, options);
assert(ret);
nanort::BVHBuildStatistics stats = accel.GetStatistics();
printf("  BVH statistics:\n");
printf("    # of leaf   nodes: %d\n", stats.num_leaf_nodes);
printf("    # of branch nodes: %d\n", stats.num_branch_nodes);
printf("  Max tree depth   : %d\n", stats.max_tree_depth);

std::vector<float> rgb(width * height * 3, 0.0f);
const float tFar = 1.0e+30f;
// Shoot rays.
#ifdef _OPENMP
#pragma omp parallel for
#endif
for (int y = 0; y < height; y++) {
  for (int x = 0; x < width; x++) {
    BVHTraceOptions trace_options;
    // Simple camera. change eye pos and direction fit to .obj model.
    nanort::Ray<float> ray;
    ray.min_t = 0.0f;
    ray.max_t = tFar;
    ray.org[0] = 0.0f;
    ray.org[1] = 5.0f;
    ray.org[2] = 20.0f;
    float3 dir;
    dir[0] = (x / (float)width) - 0.5f;
    dir[1] = (y / (float)height) - 0.5f;
    dir[2] = -1.0f;
    dir.normalize();
    ray.dir[0] = dir[0];
    ray.dir[1] = dir[1];
    ray.dir[2] = dir[2];

    nanort::TriangleIntersector<> triangle_intersecter(mesh.vertices, mesh.faces, /* stride */sizeof(float) * 3);
    nanort::TriangleIntersection<> isect,
    bool hit = accel.Traverse(ray, triangle_intersector, &isect, trace_options);
    if (hit) {
      // Write your shader here.
      float3 normal;
      unsigned int fid = triangle_intersector.intersect.prim_id;
      normal[0] = mesh.facevarying_normals[3*3*fid+0]; // @todo { interpolate normal }
      normal[1] = mesh.facevarying_normals[3*3*fid+1];
      normal[2] = mesh.facevarying_normals[3*3*fid+2];
      // Flip Y
      rgb[3 * ((height - y - 1) * width + x) + 0] = fabsf(normal[0]);
      rgb[3 * ((height - y - 1) * width + x) + 1] = fabsf(normal[1]);
      rgb[3 * ((height - y - 1) * width + x) + 2] = fabsf(normal[2]);
    }
  }
}

Defines

NANORT_USE_CPP11_FEATURE : Enable C++11 feature
NANORT_ENABLE_PARALLEL_BUILD : Enable parallel BVH build(OpenMP version is not yet fully tested).

More example

See examples directory for example renderer using NanoRT.

• [x] examples/path_tracer Path tracer example by https://github.com/daseyb
  • [x] Better ortho basis generation: Building an Orthonormal Basis, Revisited http://jcgt.org/published/0006/01/01/
• [x] examples/bidir_path_tracer Bi-directional path tracer example by https://github.com/tatsy
• [x] examples/gui Simple renderer with GUI(using ImGui)
• [x] examples/vrcamera Stereo VR Camera
• [x] examples/objrender Render wavefront .obj model using NanoRT.
• [x] examples/par_msquare Render heightfield by converting it to meshes using par_msquare(marching squares)
• [x] examples/las Visualize LiDAR(LAS) point cloud as sphere geometry.
• [x] examples/double_precision Double precision triangle geometry and BVH.
• [x] examples/embree-api NanoRT implementation of Embree API.
• [x] examples/ptex Ptex texturing.

<!-- ### Screenshots Raytracing allows to implement different camera models quite easily. See [examples/gui](examples/gui) for different camera models which can be set via the `config.json` or the GUI itself: * `perspective`\  * `orthographic`\  * `spherical` FoV 120 & 180:\   * `spherical-panorama` FoV 120 & 180:\   * `cylindrical`: FoV 90 & 120:\   * `fish-eye`: FoV 120 & 180:\   * `fish-eye MKX22`: nonlinear fish-eye lens "iZugar MKX22 Fisheye Lens" with fixed FoV 220:\  -->

Custom geometry

Here is an example of custom geometry.

• [x] Spheres(particles) examples/particle_primitive/
• Cubic Bezier Curves
  • [x] Approximate as lines examples/curves_primitive/
  • [ ] Recursive Ray-Bezier intersection.
• [x] Cylinders examples/cylinder_primitive/

And plesae see API at wiki: https://github.com/lighttransport/nanort/wiki/API

License