Physically Based Rendering is a free CC-licensed textbook coupling rendering theory with a full implementation

Physically Based Rendering: From Theory to Implementation (3rd edition, 2018) by Pharr, Jakob, and Humphreys is a comprehensive photorealistic-rendering textbook, freely readable online under CC-BY-NC-ND 4.0. Its distinguishing approach couples the theory with a complete implementation of a fully functional rendering system (the pbrt renderer), written in a literate-programming style. Its table of contents spans geometry, shapes, radiometry, camera models, reflection models, materials, textures, volume scattering, light sources, Monte Carlo integration, and light transport — making it the definitive technical reference for physically based rendering and ray tracing.

Examples

Chapter 5 covers radiometry (radiance, irradiance, flux). Chapter 8 covers reflection models (BRDF, microfacet). Chapters 14-16 cover light transport including path tracing.

Assessment

Name three subject areas covered in the PBR book directly relevant to GPU shader programming, and explain how each applies to fragment shaders.