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.
- (Some example applications use C++-11 feature, though)
- 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
- Benefitical 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/

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
  T inv_dir[3];    // filled internally
  int dir_sign[3]; // filled internally
} 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 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, nanort::TriangleMesh<float>, nanort::TriangleSAHPred<float>, nanort::TriangleIntersector<> > 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;

// Returns nearest hit point(if exists)
BVHTraceOptions trace_options; // optional
bool hit = accel.Traverse(ray, triangle_intersecter, 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, nanort::TriangleMesh<float>, nanort::TriangleSAHPred<float>,nanort::TriangleIntersector<> > 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);
    bool hit = accel.Traverse(ray, trace_options, triangle_intersector);
    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]);
    }
  }
}

More example

See examples directory for example renderer using NanoRT.

Custom geometry

Here is an example of custom geometry.

Spheres(particles) examples/particle_primitive/
Cubic Bezier Curves
- Approximate as lines examples/curves_primitive/
- Recursive ray-Bezier intersection.
Cylinders examples/cylinder_primitive/

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

License

nanort.h is licensed under MIT license.

NanoRT uses stack_container.h which is licensed under:

// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

NanoRT examples use some external third party libraries. Licenses for such third party libraries obey their own license.

TODO

PR are always welcome!

NickVoron/nanort