Introduction to lightmaps and baking

Lightmapping is the process of pre-calculating the brightness of surfaces in a Scene, and storing the result in a Texture called a lightmap for later use.

Lightmaps can include both direct and indirect light. This lighting texture can be used together with surface information like color (albedo) and relief (normals) by the Shader associated with an object’s material.

The data baked into lightmaps cannot change at runtime. Real-time lights can be overlaid and used additively on top of a lightmapped scene, but cannot interactively change the lightmaps themselves.

With this approach, we trade the ability to move our lights at gameplay for a potential increase in performance, suiting less powerful hardware such as mobile platforms.

Unity bakes lightmaps with the Progressive Lightmapper.

For advice on setting up a lightmapper, see Lightmapping: Getting started.

Structure of a lightmap

• A: A UV chart. A distinct shape in the lightmap, for example one face of a cube. Each UV chart has a margin around it that separates it from other UV charts.
• B: A UV layout. The set of UV charts for one mesh, for example the six faces of a cube. Each UV layout has padding around it, to separate it from other UV layouts that Unity packs into the same UV atlas.

The Progressive Lightmapper

The Progressive Lightmapper is a fast path-tracing-based lightmapper system that provides baked lightmaps and Light Probes with progressive updates in the Editor. It requires non-overlapping UV charts with small area and angle errors, and sufficient margin between UV charts.

The Progressive Lightmapper takes a short preparation step to process geometry and instance updates, and generates the G-buffer and chart masks. It then produces the output immediately and progressively refines it over time for a much-improved interactive lighting workflow. Additionally, baking times are much more predictable because the Progressive Lightmapper provides an estimated time while it bakes.

The Progressive Lightmapper also bakes global illumination (GI) at the lightmap resolution for each texel individually, without upsampling schemes or relying on any irradiance caches or other global data structures. This makes it robust and allows you to bake selected portions of lightmaps, which makes it faster for you to test and iterate on your Scene.

For an in-depth video showing the interactive workflow, see Unity’s video walkthrough: In Development - Progressive Lightmapper (YouTube).