Baked Lighting

Baked lighting is fundamentally predicated on a static scene. The geometry, materials, and light sources involved in the precomputation cannot change at runtime. This includes:

• Immovable objects: Walls, floors, and architectural elements.
• Static lights: Sunlight, sky illumination, and fixed interior lights.
• Unchanging materials: Surface properties like albedo and roughness. Any dynamic element, like a moving character or a switched-on flashlight, requires separate, real-time lighting techniques.

The core process involves offline precomputation using a path tracer or radiosity solver to simulate complex light transport like global illumination, color bleeding, and soft shadows. The results are baked into texture maps called lightmaps.

• UV Unwrapping: Each static object requires a second set of texture coordinates (UVs) to map the 3D surface to the 2D lightmap.
• Texel Resolution: The density of this mapping determines lighting detail; higher resolution increases memory cost.
• Storage: Lightmaps typically store baked irradiance or final shaded color, which is multiplied with the material's albedo at runtime.

This technique offers an extreme performance-for-memory trade-off. Runtime shading is reduced to a simple texture fetch and multiply, enabling complex lighting on low-end hardware.

• Performance Gain: Eliminates costly real-time GI, shadow, and bounce light calculations per frame.
• Memory Cost: Lightmaps can consume significant video memory (VRAM). A complex scene may require hundreds of MBs in lightmap data.
• Bandwidth: The precomputed data must be loaded into memory, impacting asset streaming and load times.

Baked lighting cannot represent high-frequency dynamic effects because it is a precomputed snapshot. This includes:

• Real-time shadows from moving objects.
• Dynamic time-of-day changes (e.g., moving sun).
• Interactive light sources (e.g., turning lights on/off).
• Specular highlights from moving lights or the viewer. These limitations necessitate a hybrid rendering approach, combining baked static lighting with dynamic techniques for interactive elements.

The baking process can introduce visual artifacts that require careful management:

• Light Bleeding: Unwanted colored light leaking through thin geometry or seams, caused by low-resolution sampling or UV packing issues.
• Seams: Visible discontinuities in lighting at UV chart boundaries.
• Texel Density Mismatches: Differing lighting resolution across surfaces causing blurry or blocky spots.
• Shadow Acne: Self-shadowing artifacts due to floating-point precision issues during the bake. Mitigation involves artist-driven workflows for UV layout, probe placement, and bake settings.

In contemporary Physically Based Rendering (PBR) engines, baked lighting is rarely used in isolation. It integrates into a deferred or forward+ rendering pipeline as one component:

• Light Probes: Capture indirect lighting from the bake for dynamic objects.
• Reflection Probes: Pre-filter environment maps for specular reflections.
• Ambient Occlusion (AO) Maps: Often baked separately or combined into the lightmap.
• Hybrid GI: Baked lighting provides base indirect illumination, which is then combined with real-time direct lighting and screen-space techniques for a fully dynamic appearance.

A set of algorithms that simulate the complex, multi-bounce behavior of light in a scene. It accounts for indirect lighting, color bleeding, and soft shadows created when light reflects between surfaces.

• Path Tracing is a common Monte Carlo method for computing GI.
• Baked lighting is a performance optimization where GI solutions for static elements are precomputed.

A rendering methodology grounded in real-world physics. It uses energy-conserving material models and physically plausible lighting to achieve consistent, realistic results under various lighting conditions.

• Core principles include metallic/roughness or specular/glossiness workflows.
• Baked lighting often stores the results of PBR calculations into lightmaps for real-time use.

A texture map that stores precomputed lighting information (brightness and color) for the surfaces of static 3D geometry. This is the primary data structure for baked lighting.

• UV2 Channel: Lightmaps use a second, non-overlapping UV map to avoid texture stretching.
• Texel Density: The resolution of the lightmap determines lighting detail and memory cost.
• Lightmap Atlasing: Multiple objects are packed into a single texture atlas to optimize draw calls.

An advanced real-time rendering technique that precomputes how light is transferred (blocked, shadowed, reflected) within a rigid scene. The results are stored in mathematical basis functions like Spherical Harmonics.

• Enables dynamic, low-frequency lighting and soft shadows on static scenes.
• More flexible than traditional baked lighting but has higher precomputation and storage costs.

The process of estimating underlying scene properties—geometry, materials (BRDF), and lighting—from a set of 2D photographs. It effectively inverts the traditional graphics pipeline.

• Photometric Stereo is a classic inverse rendering technique for estimating normals.
• Modern approaches use differentiable rendering and neural networks.
• The output material and lighting data can be used to bake new lighting scenarios.

Real-time GI techniques that compute indirect lighting on the fly for dynamic objects and lighting. This contrasts with the static nature of baked lighting.

• Voxel-Based GI: Uses a 3D grid of voxels to propagate light in real-time.
• Screen-Space GI (SSGI): Approximates indirect lighting using data from the current frame's depth and color buffers.
• Ray-Traced GI: Uses hardware ray tracing for accurate, dynamic multi-bounce lighting.