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tinybvh

Single-header BVH construction and traversal library written as "Sane C++" (or "C with classes"). Some C++11 is used, e.g. for threading. The library has no dependencies.

tinyocl

Single-header OpenCL library, which helps you select and initialize a device. It also loads, compiles and runs kernels, with several convenient features:

Rendered with tinybvh

To use tinyocl, just include tiny_ocl.h; this will automatically cause linking with OpenCL.lib in the 'external' folder, which in turn passes on work to vendor-specific driver code. But all that is not your problem!

Note that the tiny_bvh.h library will work without tiny_ocl.h and remains dependency-free. The new tiny_ocl.h is only needed in projects that wish to trace rays on the GPU using BVHs created by tiny_bvh.h.

BVH?

A Bounding Volume Hierarchy is a data structure used to quickly find intersections in a virtual scene; most commonly between a ray and a group of triangles. You can read more about this in a series of articles on the subject: https://jacco.ompf2.com/2022/04/13/how-to-build-a-bvh-part-1-basics .

Right now tiny_bvh comes with the following builders:

Several special-purpose builders are also available:

A constructed BVH can be used to quickly intersect a ray with the geometry, using BVH::Intersect or BVH::IsOccluded, for shadow rays. The double-precision BVH is traversed using BVH::IntersectEx.

The constructed BVH will have a layout suitable for construction ('WALD_32BYTE'). Several other layouts for the same data are available, which all serve one or more specific purposes. You can convert between layouts using BVH::Convert. The available layouts are:

A BVH in the BVH::WALD_32BYTE format may be refitted in case the triangles moved using BVH::Refit. Refitting is substantially faster than rebuilding and works well if the animation is subtle. Refitting does not work if polygon counts change.

How To Use

The library tiny_bvh.h is designed to be easy to use. Please have a look at tiny_bvh_minimal.cpp for an example. A Visual Studio 'solution' (.sln/.vcxproj) is included, as well as a CMake file. That being said: The examples consists of only a single source file, which can be compiled with clang or g++, e.g.:

g++ -std=c++20 -mavx tiny_bvh_minimal.cpp -o tiny_bvh_minimal

The single-source sample ASCII test renderer can be compiled with

g++ -std=c++20 -mavx tiny_bvh_renderer.cpp -o tiny_bvh_renderer

The cross-platform fenster-based single-source bitmap renderer can be compiled with

g++ -std=c++20 -mavx -mwindows -O3 tiny_bvh_fenster.cpp -o tiny_bvh_fenster (on windows)

g++ -std=c++20 -mavx -O3 -framework Cocoa tiny_bvh_fenster.cpp -o tiny_bvh_fenster (on macOS)

The multi-threaded path tracing demo can be compiled with

g++ -std=c++20 -mavx -mwindows -O3 tiny_bvh_pt.cpp -o tiny_bvh_pt (on windows)

The performance measurement tool can be compiled with:

g++ -std=c++20 -mavx -Ofast tiny_bvh_speedtest.cpp -o tiny_bvh_speedtest

Version 1.1.2

Version 1.1.0 introduced a <ins>change to the API</ins>. The single BVH class with multiple layouts has been replaced with a BVH class per layout. You can simply instantiate the desired layout; conversion (and data ownership) is then handled properly by the library. Examples:

BVH bvh;
bvh.Build( (bvhvec4*)myTriData, triangleCount );
bvh.Intersect( ray );

BVH4_CPU bvh;
bvh.Build( (bvhvec4*)myTriData, triangleCount );
bvh.Intersect( ray );

If you wish to use a specific builder (such as the spatial splits builder) or if you need to do custom operations on the BVH, such as post-build optimizing, you can still do the conversions manually. Example:

BVH bvh;
bvh.Build( (bvhvec4*)myTriData, triangleCount );
BVH_Verbose tmp;
tmp.ConvertFrom( bvh );
tmp.Optimize( 100000 );
bvh.ConvertFrom( tmp );
printf( "Optimized BVH SAH cost: %f\n", bvh.SAHCost() );

Note that in this case, data ownership and lifetime must be managed carefully. Specifically, layouts converted from other layouts use data from the original, so both must be kept alive.

This version of the library includes the following functionality:

The current version of the library is rapidly gaining functionality. Please expect changes to the interface.

Plans, ordered by priority:

tinybvh in the Wild

A list of projects using tinybvh:

Created or know about other projects? Let me know!

Contact

Questions, remarks? Contact me at bikker.j@gmail.com or on twitter: @j_bikker, or BlueSky: @jbikker.bsky.social .

License

This library is made available under the MIT license, which starts as follows: "Permission is hereby granted, free of charge, .. , to deal in the Software without restriction". Enjoy.