The Precompute Process
In Unity, precomputed lighting is calculated in the background - either as an automatic process, or it is initiated manually. In either case, it is possible to continue working in the editor while these processes run behind-the-scenes.
When the precompute process is running, a blue progress bar will appear in the bottom right of the Editor. There are different stages which need to be completed depending on whether Baked GI or Precomputed Realtime GI is enabled. Information on the current process is shown on-top of the progress bar.
Progress bar showing the current state of Unity’s precompute.
In the example above, we can see that we are at task 5 of 11 which is, ‘Clustering’ and there are 108 jobs remaining before that task is complete and the precompute moves on to task 6. The various stages are listed below:
|Precomputed Realtime GI||Baked GI|
|01 - Create Geometry||01 - Create Geometry|
|02 - Layout Systems||02 - Atlassing|
|03 - Create Systems||03 - Create Baked Systems|
|04 - Create Atlas||04 - Baked Resources|
|05 - Clustering||05 - Bake AO|
|06 - Visibility||06 - Export Baked Texture|
|07 - Light Transport||07 - Bake Visibility|
|08 - Tetrahedralize Probes||08 - Bake Direct|
|09 - Create ProbeSet||09 - Ambient and Emissive|
|10 - Create Bake Systems|
|Probes||11 - Bake Runtime|
|12 - Upsampling Visibility|
|01 - Ambient Probes||13 - Bake Indirect|
|02 - Baked/Realtime Ref. Probes||14 - Final Gather|
|15 - Bake ProbesSet|
|16 - Compositing|
Starting a Precompute
Only static geometry is considered by Unity’s precomputed lighting solutions. To begin the lighting precompute process we need at least one GameObject marked as ‘static’ in our scene. This can either be done individually, or by shift-selecting multiple GameObjects from the hierarchy panel.
From the Inspector panel, the Static checkbox can be selected (Inspector>Static). This will set all of the GameObject’s ‘static options’, or ‘flags’, including navigation and batching, to be static, which may not be desirable. For Precomputed Realtime GI, only 'Lightmap Static' needs to be checked.
For more fine-grained control, individual static options can be set from the drop-down list accessible to the right of the Static checkbox in the Inspector panel. Additionally, objects can also be set to Static in the Object area of the lighting window.
If your scene is set to Auto (Lighting>Scene>Auto), Unity’s lighting precompute will now begin automatically. Otherwise it will need to be started manually as described below.
If ‘Auto’ is checked from the bottom of Unity’s Lighting panel (Lighting>Scene>Auto), then this precompute will begin automatically as a background process whenever changes are made to static geometry within your scene.
However, if Auto is not selected, you will need to manually start a precompute by clicking the ‘Build’ button next to it. This will begin the precompute in much the same way, while giving you control over when this process starts.
Manually initiating a precompute will cause all aspects of your scene lighting to be evaluated and (re)computed. If you wish to selectively recalculate Reflection probes by themselves, this can be done via the drop-down menu next to the Build button (Lighting>Scene>Build).
In either Baked GI or Precomputed Realtime GI, Unity ‘caches’ (stores) data about your scene lighting in the ‘GI Cache’, and will try to reuse this data whenever possible to save time during precompute. The number and nature of the changes you have made to your scene will determine how much of this data can be reused, if at all.
This cache is stored outside of your Unity project and can be cleared using (Preference>GI Cache>Clear Cache). Clearing this means that all stages of the precompute will need to be recalculated from the beginning and this can therefore be time consuming. However in some cases, where perhaps you need to reduce disk usage, this may be helpful.