🔦 RayTracer

A CPU ray tracer, built from scratch in C++, one day at a time.

No engine, no framework, no GPU — just vectors, rays, and a lot of dot products. Built over 6 days at ENSTA Paris for course CSC_4IN04_TA, in collaboration with classmate Yassine ZANNED.

↑ Day6: spheres, triangles, Phong shading, and hard shadows, all rendered pixel-by-pixel with zero external rendering libraries.

💡 What is this

The repo is a day-by-day progression (Day1 ... Day6), where each folder is a self-contained snapshot of the engine as it grew new features. Nothing is shared between folders on purpose — every day's code builds and runs standalone, so you can literally watch the renderer level up folder by folder. Day6 is the most complete and feature-rich version.

✨ Features

Based on the code in Day6 (the final/most advanced snapshot):

• Shapes — spheres (Objsphere.cpp/hpp) and triangles (ObjTriangle.cpp/hpp), both derived from a common Shape base class (Objshape.cpp/hpp)
• Camera — a simple pinhole camera generating per-pixel view rays from an aspect ratio and viewport (camera.cpp/hpp)
• Ray-object intersection — analytic ray-sphere and ray-triangle intersection tests
• Shading — Phong-style lighting with ambient, diffuse, and specular terms (computeDiffuse, computeSpecular, computeShading in main.cpp)
• Shadows — hard shadows via secondary shadow rays (Ray::IsInShadow)
• Scene loading — a basic XML scene format parsed with tinyxml2 (textParser.cpp/hpp), letting spheres, triangles, camera aspect ratio, and a single light live in a .xml file instead of being hardcoded in main.cpp (see Day6/shapes.xml)
• Output — renders straight to PNG using the header-only stb_image_write.h

Not implemented (yet): reflections, refractions, anti-aliasing/supersampling, multithreaded or GPU-accelerated rendering, other primitives (planes, meshes, etc. beyond spheres/triangles), and soft shadows / multiple light sources.

🗓️ Day-by-day progression

Day	What it adds
Day1	Sets up stb_image_write.h and writes a color-gradient PNG as a sanity check
Day2	First working ray tracer — Ray, Vector3, Camera, and ray-sphere intersection
Day3	Adds triangles (ObjTriangle) alongside spheres
Day4	Refines shading/rendering with spheres and triangles
Day5	Adds a Makefile; includes triangles, spheres, and shading
Day6	Adds XML scene loading (tinyxml2), Phong shading with shadows — the most complete build

Day1-Day5 use hardcoded (not XML-driven) scenes; Day1 only writes a gradient test image.

🛠️ Build & Run

Day6 (recommended, most complete)

Day6 has no Makefile — compile directly with a C++17-capable compiler:

cd Day6
g++ -std=c++17 -O2 main.cpp Ray.cpp Objshape.cpp Objsphere.cpp ObjTriangle.cpp camera.cpp textParser.cpp -o raytracer

Day6 depends on tinyxml2 for XML parsing. tinyxml2.h is included, but you must also provide tinyxml2.cpp (not included in this repo) or link against a system-installed tinyxml2 library:

g++ -std=c++17 -O2 main.cpp Ray.cpp Objshape.cpp Objsphere.cpp ObjTriangle.cpp camera.cpp textParser.cpp -o raytracer -ltinyxml2

Day5 (has a Makefile, hardcoded scene, no XML dependency)

cd Day5
make

Compiles all .cpp files in the folder into raytracer via g++ -std=c++17 -Wall -Wextra -O2. Run make clean to remove build artifacts.

Day1-Day4

Same idea — pass all .cpp files in the folder to g++:

cd Day2
g++ -std=c++17 -O2 *.cpp -o raytracer

Running

No command-line arguments — image dimensions, camera settings, and (for Day1-Day5) the scene contents are hardcoded in main.cpp. Run the binary from inside its day folder, since paths to companion files like shapes.xml are relative to the working directory:

cd Day6
./raytracer

The image lands as a PNG in the current directory (e.g. Day6/rayTracer.png, Day5/rayTracer.png, Day1/output/gradient1.png).

Scene format (Day6)

Day6 reads a scene from shapes.xml in the working directory. Example (Day6/shapes.xml):

<Scene>
    <Camera>
        <AspectRatio>1.777</AspectRatio>
    </Camera>
    <Light>
        <position x="10.0" y="15.0" z="20.0" />
        <color r="1.0" g="1.0" b="1.0" />
        <shininess>32.0</shininess>
    </Light>
    <Shapes>
        <Sphere>
            <position x="1.0" y="2.0" z="3.0" />
            <radius>5.0</radius>
            <color r="1.0" g="0.5" b="0.0" />
        </Sphere>
        <Triangle>
            <vertex0 x="0.0" y="0.0" z="0.0" />
            <vertex1 x="1.0" y="0.0" z="0.0" />
            <vertex2 x="0.0" y="1.0" z="0.0" />
            <color r="0.0" g="1.0" b="0.0" />
        </Triangle>
    </Shapes>
</Scene>

🐛 Known issues

The XML schema doesn't actually match. The element/attribute names actually read by TextParser::parseShapes() are flat attributes like x, radius, colorR — which differ from the nested-element style shown in shapes.xml above (e.g. <position x=... />, <radius>...</radius>). The two are not fully consistent in the current code. Treat XML scene loading as a work-in-progress feature, not a stable interface, until this is reconciled.

🖼️ Sample renders

Images produced by the engine at various stages of development:

🚀 Status / future work

This was a 6-day learning project focused on understanding ray tracing fundamentals — vectors, camera rays, intersection tests, Phong shading, shadows — rather than building a production renderer. Planned-but-not-yet-implemented directions include reflections/refractions, anti-aliasing, and parallelizing the render loop (multithreading or GPU acceleration) for faster/higher-resolution output.

License

This project is licensed under the MIT License.