NanoRT, single header only modern ray tracing kernel.

NanoRT is simple single header only ray tracing kernel.

NanoRT BVH traversal is based on mallie renderer: https://github.com/lighttransport/mallie

Features

• Portable C++
  • Only use C++-03 features.
  • Some example applications use C++-11 though.
• 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, ARM, x86, SPARC, (maybe)MIPS, etc.
• GPU effient 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/

Applications

• Test renderer for your light trasport 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

API

nanort::Ray represents ray. The origin org, the direction dir(not necessarily normalized), the minimum hit distance minT(usually 0.0) and the maximum hit distance maxT(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.

typedef struct {
  float org[3];    // [in] must set
  float dir[3];    // [in] must set
  float min_t;     // [in] must set
  float max_t;     // [in] must set
  float 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 options; // BVH build option

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

nanort::TriangleMesh triangle_mesh(vertices, faces);
nanort::TriangleSAHPred triangle_pred(vertices, faces);

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

nanort::TriangleIntersector<> triangle_intersecter(vertices, faces);
ray.min_t = 0.0f;
ray.max_t = 1.0e+30f;

nanort::Ray ray;
// fill ray org and ray dir.

// Returns nearest hit point(if exists)
BVHTraceOptions trace_options;
bool hit = accel.Traverse(ray, trace_options, triangle_intersecter);

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

For a builtin Triangle intersector,

• vertices : The array of triangle vertices(xyz * numVertices)
• faces : The array of triangle face indices(3 * numFaces)

are required attributes.

Usage

// NanoRT defines template based class, so no NANORT_IMPLEMENTATION anymore.
#include "nanort.h"

Mesh mesh;
// load mesh data...

nanort::BVHBuildOptions options; // Use default option

nanort::TriangleMesh triangle_mesh(mesh.vertices, mesh.faces);
nanort::TriangleSAHPred triangle_pred(mesh.vertices, mesh.faces);

nanort::BVHAccel<nanort::TriangleMesh, nanort::TriangleSAHPred> 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.numLeafNodes);
printf("    # of branch nodes: %d\n", stats.numBranchNodes);
printf("  Max tree depth   : %d\n", stats.maxTreeDepth);

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 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);
    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

See examples/particle_primitive/ and API wiki: https://github.com/lighttransport/nanort/wiki/API

License

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.

TODO

PR are always welcome!

• Optimize ray tracing kernel
  • Efficient Ray Tracing Kernels for Modern CPU Architectures http://jcgt.org/published/0004/04/05/
• Scene graph support.
  • Instancing support.
• Optimize Multi-hit ray traversal for BVH.
  • http://jcgt.org/published/0004/04/04/
• Ray traversal option.
  • FaceID range.
  • Double sided on/off.
  • Ray offset.
  • Avoid self-intersection.
  • Custom intersection filter.
• Fast BVH build
  • Bonsai: Rapid Bounding Volume Hierarchy Generation using Mini Trees http://jcgt.org/published/0004/03/02/
• Support various primitive types
  • Spheres(particles) examples/particle_primitive/
  • Bezier Curves
  • Cylinders