Custom C++ Ray Tracer | Alireza Parchami

**TL;DR:** Co-developed a custom multithreaded CPU ray tracing engine in **C++** to render a complex, stylized 3D scene. Extending a baseline framework, my teammate and I engineered core computer graphics and ray-tracing algorithms for spatial acceleration, light transport, and physically based rendering.

Final Rendered Image from Our Custom Ray-Tracer

### ⚙️ Core Technical Features We engineered custom logic to solve specific rendering challenges: **1. Procedural Volumetrics (Double-Sided Primitives)** Our procedural confetti relies on randomly rotated discs. We engineered custom double-sided normal calculations so rays hitting the "back" of the confetti still evaluate color correctly, preventing black artifacts.

Double-Sided Discs

**2. Transmissive Light Transport ("Magic Glass")** Standard glass primitives block shadow rays, creating unrealistic dark voids. We modified the recursive ray-tracing integrator so external light passes through the globe, while preventing internal point lights from casting false, enlarged shadows outside.

Shadows from Inside

No Outside Shadows

Illumination from Outside

**3. Physically Based Camera (Depth of Field)** By simulating a physical lens aperture and focal plane, we added Depth of Field to naturally guide the viewer's eye to the snowman while blurring the background lighting.

**4. Surface Normal Perturbation (Bump Mapping)** We applied noise-based and wood-grain bump maps to the walls and shelves to break up the flat CGI look, calculating surface normal modifications during the shading phase.

**5. Performance & Optimization** * **Bounding Volume Hierarchy (BVH):** Implemented spatial acceleration to optimize ray-primitive intersection tests for the high-polygon imported snowman. * **Mesh Instancing:** Expanded the engine's loading pipeline to support instancing, drastically reducing the memory footprint of duplicated 3D assets.

Instancing Objects

BVH

This project was a fantastic deep dive into rendering equations, spatial data structures, and the intersection of software engineering and digital art. It was a part of our Computer Graphics course offered by [CG-Group of Saarland University](https://graphics.cg.uni-saarland.de/courses/cg1-2021/index.html).

### 📖 Project Deep Dive: Engineering the Scene As part of my Computer Graphics coursework, I collaborated in a team of two to develop a custom CPU-based ray tracer in C++. While the base framework provided the core multithreading architecture, our team was responsible for implementing the fundamental ray-tracing physics, math logic, and a suite of advanced rendering features to bring our final scene to life. Our final render, titled **"The Lonely Snowman,"** tells the story of the last snow globe left on a Christmas market shelf. ## 🚀 Engine Features & Technical Implementation To achieve a photorealistic and cinematic result, we engineered several advanced features into the rendering pipeline: ### 1. Bounding Volume Hierarchy (BVH) Acceleration Ray tracing thousands of confetti discs alongside a high-polygon imported snowman mesh is incredibly computationally expensive. We implemented a **Bounding Volume Hierarchy (BVH)** spatial acceleration structure to optimize ray-primitive intersection tests, drastically reducing our overall rendering time. ### 2. "Magic Glass" (Custom Integrator Logic) Rendering the glass snow globe presented a complex challenge regarding shadow rays and transmissive materials. - **The Problem:** Our original glass implementation blocked shadow rays, preventing objects inside the globe from receiving outside light and casting harsh, unrealistic shadows. Furthermore, having point lights _inside_ the globe created false illumination and enlarged shadows outside the sphere. - **The Solution:** We modified the `recraytrace` (recursive ray tracing) integrator to cast shadow rays with higher material-awareness. When a shadow ray intersects an object, the integrator checks the material type. If it intersects glass, the shadow is ignored, allowing light to pass through. We added specific conditional logic: light from the outside can illuminate the interior, but light originating from inside the globe cannot cast shadows outside. ### 3. Double-Sided Primitives for Volumetrics The confetti inside the globe was created by randomly sampling points within the sphere, assigning them random rotations and colors. - **The Challenge:** Our standard `Disc` primitive was one-sided, meaning light rays hitting the back face returned black, ruining the illusion of colorful confetti. - **The Solution:** Using object-oriented principles, we derived a custom `DoubleSidedDisc` class from the original `Disc` class, ensuring that normal calculations and color evaluations worked correctly regardless of the ray's incident angle. ### 4. Physically Based Camera Effects - **Depth of Field (DoF):** To give the render a cinematic feel and direct the viewer's eye to the "lonely" snowman, we implemented Depth of Field. By simulating a physical camera aperture and focal plane, we achieved a realistic bokeh blur on the background lights and shelves. ### 5. Advanced Texturing & Asset Management - **Bump Mapping:** To break up the flat CGI look of the background, we implemented bump mapping. We applied a noise-based bump map to the walls for a plaster-like texture and a wood grain pattern to the shelves, calculating surface normal perturbations during the shading phase. - **Mesh Instancing:** We expanded the engine's asset loaders to support instancing. This allowed us to duplicate complex imported objects in memory without linear memory overhead. (We initially tested this by giving the snowman a friend, but reverted to a single snowman to maintain the artistic theme!).

This project was a fantastic deep dive into rendering equations, spatial data structures, and the intersection of software engineering and digital art.