Building a Ray Tracer from Scratch: A Journey into 3D Rendering

There’s something deeply satisfying about building a rendering system from scratch. Over the past few months, I’ve been working on a software ray tracer to understand the fundamental mathematics behind how computers generate photorealistic images. The journey from empty C++ files to my first successful render has taught me more about 3D graphics than any tutorial could.

Why Build a Ray Tracer?

Modern graphics APIs like OpenGL and DirectX abstract away many of the core concepts of 3D rendering. While this is great for productivity, it can leave gaps in understanding how light, geometry, and mathematics combine to create the images we see on screen.

Ray tracing, in particular, offers an elegant conceptual model: for each pixel, cast a ray from the camera through that pixel into the scene, and calculate what color that ray “sees” when it hits objects. This mirrors how vision actually works in the real world.

Starting with Ray-Plane Intersection

My first milestone was implementing ray-plane intersection-one of the most fundamental operations in ray tracing. A ray is defined mathematically as:

ray(t) = origin + t * direction

Where t is a parameter that scales along the ray’s direction. A plane can be defined by a point on the plane and a normal vector. The intersection occurs where the ray meets the plane, which involves solving for the value of t.

Getting that first intersection working felt like unlocking a door to 3D mathematics. Suddenly, abstract vector operations had concrete visual meaning.

The Smiley Face Scene

My first successful render was a simple smiley face scene-two circles for eyes and a curve for the mouth, all rendered as intersections with geometric planes. It wasn’t photorealistic, but seeing those familiar shapes emerge from mathematical calculations was incredibly rewarding.

This simple scene tested several key components:

• Ray generation: Creating rays from camera through each pixel
• Intersection testing: Finding where rays hit geometry
• Basic shading: Converting intersection data to pixel colors
• Coordinate systems: Ensuring all math operations use consistent spaces

Following Peter Shirley’s Tutorial

To build on my foundation, I implemented Peter Shirley’s famous “Ray Tracing in a Weekend” tutorial. This tutorial is brilliant because it builds up a complete ray tracer incrementally, starting with basic concepts and adding features like:

• Multiple object types: Spheres, planes, and other primitives
• Material systems: Diffuse, metallic, and dielectric materials
• Anti-aliasing: Sampling multiple rays per pixel for smoother images
• Camera controls: Positioning and orienting the virtual camera

Successfully recreating the tutorial’s cover image was a major milestone. The image features several spheres with different materials, demonstrating reflections, refractions, and realistic lighting-all computed using pure ray tracing algorithms.

Technical Challenges and Solutions

Performance Considerations

Software ray tracing is computationally expensive. Each pixel might require casting hundreds of rays (for anti-aliasing and global illumination), and each ray might bounce multiple times through the scene. Early versions of my ray tracer took minutes to render simple scenes.

Optimization strategies I explored:

• Bounding volume hierarchies: Organizing scene geometry for faster intersection testing
• Multi-threading: Distributing pixel calculations across CPU cores
• Early termination: Stopping ray bounces when contribution becomes negligible

Mathematical Precision

Working with floating-point arithmetic in 3D space requires careful attention to precision. Small numerical errors can compound, causing visual artifacts like “shadow acne” (incorrect self-shadowing) or missed intersections.

Solutions included:

• Epsilon values: Adding small offsets to prevent self-intersection
• Robust intersection formulas: Using stable mathematical formulations
• Careful coordinate transformations: Maintaining precision through matrix operations

Beyond Basic Ray Tracing

Once I had a working ray tracer, the possibilities for extension became exciting:

Ray-Triangle Intersection: Moving beyond simple primitives to support arbitrary mesh geometry. This involves more complex mathematics but opens up the possibility of rendering real 3D models.

Advanced Materials: Implementing physically-based rendering (PBR) materials that accurately simulate how light interacts with different surfaces.

Global Illumination: Adding indirect lighting effects like color bleeding and ambient occlusion.

Volumetric Rendering: Simulating atmospheric effects like fog, smoke, and subsurface scattering.

Lessons for Software Engineering

Building a ray tracer taught me valuable lessons that apply beyond graphics programming:

Mathematical Modeling: Breaking down complex visual phenomena into mathematical components that can be computed systematically.

Performance vs. Quality Trade-offs: Every rendering feature has computational costs. Understanding these trade-offs helps make informed decisions about system architecture.

Incremental Development: Starting with basic functionality and iteratively adding features mirrors good software development practices.

Testing with Visual Output: Graphics programming provides immediate visual feedback, making it easier to spot bugs and validate correctness.

The Artistic Connection

What surprised me most was how building technical rendering systems deepened my appreciation for digital art. Understanding how light transport works, how materials interact with illumination, and how camera parameters affect the final image gave me new respect for the artistry involved in 3D rendering.

The technical and artistic sides of computer graphics aren’t separate-they’re deeply intertwined. Mathematical precision enables artistic expression, while aesthetic goals drive technical innovation.

Next Steps

My ray tracer journey is far from over. Current goals include:

• Implementing triangle mesh support for complex geometry
• Adding more sophisticated material models
• Exploring GPU acceleration for real-time performance
• Investigating advanced techniques like bidirectional path tracing

Resources and Learning

For anyone interested in building their own ray tracer, I highly recommend:

• Peter Shirley’s “Ray Tracing in One Weekend” series
• “Physically Based Rendering” by Pharr, Jakob, and Humphreys
• The ray tracing community on Twitter and various forums

The combination of mathematical challenge and visual reward makes ray tracing one of the most satisfying areas of computer graphics to explore.

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Interested in graphics programming or ray tracing? I’d love to discuss techniques, share resources, or collaborate on visual projects. Reach out on Twitter or email me at ty@tytr.dev.