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++
- Does not require C++11 compiler.
BVH spatial data structure for efficient ray intersection finding.
- Should be able to handle ~10M triangles scene efficiently with moderate memory consumption
Triangle mesh only.
- Facevarying attributes(tex coords, vertex colors, etc)
Cross platform
- MacOSX, Linux, Windows, ARM, x86, SPARC, 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/
Multi-Hit ray traversal.

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

API

nanort::Ray represents ray. nanort::Intersection stores intersection information. .t must be set to max distance(e.g. 1.0e+30f) before ray traversal. nanort::BVHAccel builds BVH data structure from geometry, and provides the function to find intersection point for a given ray. nanort::BVHTraceOptions specifies ray traverse/intersection options.

typedef struct {
  float t;             // [inout] hit distance.
  float u;             // [out] varycentric u of hit triangle.
  float v;	       // [out] varicentric v of hit triangle.
  unsigned int faceID; // [out] face ID of hit triangle.
} Intersection;

typedef struct {
  float org[3];   // [in] must set
  float dir[3];   // [in] must set
  float minT;     // [in] must set
  float maxT;     // [in] must set
  float invDir[3];// filled internally
  int dirSign[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 faceIdsRange[2]; 
  bool cullBackFace; // default: false
};

nanort::BVHBuildOptions options; // BVH build option
nanort::BVHAccel accel;
accel.Build(vertices, faces, numFaces, options);

nanort::Intersection isect;
isect.t = 1.0e+30f;

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

// Returns nearest hit point(if exists)
BVHTraceOptions traceOptions;
bool hit = accel.Traverse(isect, mesh.vertices, mesh.faces, ray, traceOptions);

// Multi-hit ray traversal
nanort::StackVector<nanort::Intersection, 128> isects;
int maxIsects = 8;
bool hit = accel.MultiHitTraverse(isects, maxIsects, mesh.vertices, mesh.faces, ray, traceOptions);

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

vertices : The array of triangle vertices(xyz * numVertices)
faces : The array of triangle face indices(3 * numFaces)
uvs, normals, custom vertex attributes : We recommend the application define vertex attributes as facevarying.

Usage

// Do this only for *one* .cc file.
#define NANORT_IMPLEMENTATION
#include "nanort.h"

Mesh mesh;
// load mesh data...

nanort::BVHBuildOptions options; // Use default option

printf("  BVH build option:\n");
printf("    # of leaf primitives: %d\n", options.minLeafPrimitives);
printf("    SAH binsize         : %d\n", options.binSize);

nanort::BVHAccel accel;
ret = accel.Build(mesh.vertices, mesh.faces, mesh.numFaces, 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++) {
    nanort::Intersection isect;

    BVHTraceOptions traceOptions;

    // Simple camera. change eye pos and direction fit to .obj model. 

    nanort::Ray ray;
    ray.minT = 0.0f;
    ray.maxT = 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];

    bool hit = accel.Traverse(isect, mesh.vertices, mesh.faces, ray, traceOptions);
    if (hit) {
      // Write your shader here.
      float3 normal;
      unsigned int fid = isect.faceID;
      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 example directory for example renderer using NanoRT.

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!

lamarqua/nanort