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.

Screenshots

Raytracing allows to implement different camera models quite easily. See 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.

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.

Lucy statue model is from The Stanford 3D Scanning Repository http://graphics.stanford.edu/data/3Dscanrep/

TODO

PR are always welcome!

lighttransport/nanort

lighttransport

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