Tracer

This is a minimal (unoptimized, feature-sparse) from-scratch implementation of a path tracer. The implementation almost all directly follows the book series Ray Tracing in One Weekend by Peter Shirley, Trevor David Black, and Steve Hollasch. There are, however, a few additional features implemented in this version (outlined below), as well as a few minor divergences in implementation and code style.

Note

See the blog post in which I explain path tracing.

Additional features

In addition to the features covered in the Ray Tracing in One Weekend Series, this renderer implements the following additional features:

• basic multithreading (see src/threads.h)
• ability to resume interrupted renders (see the interrupt handler in src/tracer.cc)
• additional 2D primitives (see src/shape2d.h)
• general affine transformations (see src/hittable.h and src/linalg.h)
• STL mesh loading (see src/mesh.h)
• from-scratch PPM image loading (see src/image.h)
• more documentation; cleaner, more generic APIs

Compilation

The build process is orchestrated by GNU Make. The following Make targets are implemented (among others):

• all: default target; compile renderer
• render: build & render, outputting to renders/render.ppm
• resume: build & resume previously-interrupted render (which must be located at renders/render.ppm)
• clean: delete compilation artifacts & binaries

Scenes included

Scenes are defined in .inc files, located in src/scenes. Each scene file should implement the function,

void build_scene(HittableList& scene, HittableList& lights, Camera& cam);

in which the scene is populated and the camera configured. The scene is then selected by including the appropriate file in tracer.cc, such as

#include "scenes/01_bouncing_spheres.inc"

Notable scenes included in this project are

• 07_cornell_box.inc: the classic Cornell Box test scene
• 10_demo_render.inc: the final render from book 2 of the Ray Tracing in One Weekend Series
• 12_dragon.inc: a render of a complex high-poly dragon mesh (expect about 3 days to render)

Limitations & future expansions

Here are some features that are missing from the current implementation, which I would like to implement in the future (pull requests are welcome):

• constructive solid geometry (unions, intersections, etc)
• a glossy bidirectional reflectance distribution function
• a torus primitive (this is algebraically tricky; ray intersections require solving a quartic)
• non-convex volumes
• PDFs for hittables other than spheres / parallelograms (boxes, other 2D primitives like ellipses); this is needed for Camera::render to support these hittables as lights
• Metropolis light transport
• general framework for motion in scene
• PDF for sampling moving sphere
• support for image formats other than .ppm
• support for 3D model formats other than .stl

Disclaimers

None of the models in models or the images in images are included under the license of this repository. I do not claim ownership for any of these; they serve only as test cases for the renderer.