Yocto/GL: Tiny C++ Libraries for Physically-based Graphics
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readme.md

Yocto/GL: Tiny C++ Libraries for Physically-based Graphics

Yocto/GL is a collection of utility C++14 libraries for building physically-based graphics algorithms released under the MIT license. Features include:

  • convenience math functions for graphics
  • static length vectors for 2, 3, 4 length of arbitrary type
  • static length matrices for 2x2, 3x3, 4x4 of arbitrary type
  • static length rigid transforms (frames), specialized for 2d and 3d space
  • linear algebra operations and transforms
  • axis aligned bounding boxes
  • rays and ray-primitive intersection
  • point-primitive distance and overlap tests
  • normal and tangent computation for meshes and lines
  • generation of tesselated meshes
  • mesh refinement with linear tesselation and Catmull-Cark subdivision
  • keyframed animation, skinning and morphing
  • random number generation via PCG32
  • simple image data structure and a few image operations
  • simple scene format
  • generation of image examples
  • generation of scene examples
  • procedural sun and sky HDR
  • procedural Perlin noise
  • BVH for intersection and closest point query
  • Python-like path operations
  • immediate mode command line parser
  • simple logger
  • path tracer supporting surfaces and hairs, GGX and MIS
  • support for loading and saving Wavefront OBJ and Khronos glTF
  • OpenGL utilities to manage textures, buffers and prograrms
  • OpenGL shader for image viewing and GGX microfacet and hair rendering

The current version is 0.5.0.

Yocto/GL is written in C++14 and compiles on OSX (clang from Xcode 9+), Linux (gcc 6+, clang 4+) and Windows (MSVC 2015, MSVC 2017). For compilation options, check the individual libraries.

Here are two images rendered with the builtin path tracer, where the scenes are crated with the test generator.

Yocto/GL

Yocto/GL

Credits

This library includes code from the PCG random number generator, boost hash_combine, base64 encode/decode by René Nyffenegger and public domain code from github.com/sgorsten/linalg, gist.github.com/badboy/6267743 and github.com/nothings/stb_perlin.h. Other external libraries are included with their own license.

Libraries

Yocto/GL is split into many small libraries to make code navigation easier.

  • yocto_math.h: fixed-size vectors, matrices, frames, transforms, bounding boxes, rays
  • yocto_image.{h,cpp}: image container, image loading and saving, tone mapping, procedural sun-sky, image examples, image utlities
  • yocto_shape.{h,cpp}: 3D shapes utilities, shape tesselation, Catmull-Clark subdivision surfaces, primitive shape generation, procedural hair
  • yocto_bvh.{h,cpp}: ray-scene intersection and closest point queries accelerated by a two-level bounding volume hierarchy
  • yocto_scene.{h,cpp}: simple scene data structure for demos and path tracing
  • yocto_sceneio.{h,cpp}: loading and saving of scene data structure
  • yocto_trace.{h,cpp}: path tracing with GGX material, hair and point shading, mesh lights, environment illumination, all with MIS sampling
  • yocto_obj.{h,cpp}: Wavefront OBJ loading and saving
  • yocto_gltf.{h,cpp}: Khronos glTF loading and saving
  • yocto_glutils.{h,cpp}: OpenGL utilities, GLFW and dear ImGui UIs wrapper

Example Applications

You can see Yocto/GL in action in the following applications written to test the library:

  • yview.cpp: simple OpenGL viewer for OBJ and glTF scenes
  • ytrace.cpp: offline path-tracer
  • yitrace.cpp: interactive path-tracer
  • yscnproc.cpp: scene manipulation and conversion to/from OBJ and glTF
  • yimview.cpp: HDR/PNG/JPG image viewer with exposure/gamma tone mapping
  • yimproc.cpp: offline image manipulation.

You can build the example applications using CMake with mkdir build; cd build; cmake ..; cmake --build

Compilation

This library requires a C++14 compiler and is know to compiled on OsX (Xcode >= 8), Windows (MSVC 2017) and Linux (gcc >= 6, clang >= 4).

For image loading and saving, Yocto/GL depends on stb_image.h, stb_image_write.h, stb_image_resize.h and tinyexr.h. To support Khronos glTF, Yocto/GL depends on json.hpp. All dependencies are included in the distribution.

OpenGL utilities include the OpenGL libraries, use GLEW on Windows/Linux, GLFW for windows handling and Dear ImGui for UI support. Since OpenGL is quite onerous and hard to link, its support can be disabled by defining YGL_OPENGL to 1 before including this file. If you use any of the OpenGL calls, make sure to properly link to the OpenGL libraries on your system. For ImGUI, build with the libraries imgui.cpp, imgui_draw.cpp, imgui_impl_glfw_gl3.cpp.

Design Considerations

Yocto/GL tries to follow a "data-driven programming model" that makes data explicit. Data is stored in simple structs and access with free functions or directly. All data is public, so we make no attempt at encapsulation. We do this since this makes Yocto/GL easier to extend and quicker to learn, which a more explicit data flow that is easier to use in parallel. Since Yocto/GL is mainly used for research and teaching, explicit data is both more hackable and easier to understand.

The use of templates in Yocto was the reason for many refactorings, going from no template to heavy template use. After many changes, we settled on using templates following the established convention in the C++ standard library.

We make use of exception for error reporting. This makes the code much cleaner and more in line with the expectation of most other programming languages.

Finally, we import math symbols from the standard library rather than using the std::name pattern. This makes math code cleaner for our domain.