The description of the Stationary type of mobility states that the shadowing of a light source with it must be baked by Lightmass:
But as of 5.7.4 (the same issue was present in 5.7.3, by the way), this is not the case - Stationary light can only produce dynamic shadows which are never baked into Lightmass.
You can easily reproduce the problem yourself:
- Create a new project.
- In the project settings: set
Static Baked Lighting= Enabled,Global Illumination Method= None (instead of Lumen),Reflection Method= None (instead of Lumen),Shadow Map Method=Shadow Maps(instead ofVirtual Shadow Maps). Restart the editor to apply changes. - Create a new empty level and open it.
- Add “Cube” from the “Quickly add to the project” menu. It will create a Static Mesh actor with its mobility set to Static. Increase its scale in X and Y directions for convenience.
- Add another “Cube” and place it on top of the first static mesh. Set
Dynamic Shadow= false in its properties (it can still cast static shadows). - Add a Directional Light. Its default mobility is Stationary.
- Press Build->
Build Lighting Only. As you can see, the lower mesh does not receive the shadow of the upper mesh even though it should.
This issue is honestly infuriating because there is a difference in how static and dynamic shadows are rendered. For example, proper soft shadows can only be static (dynamic shadows can be soft too, but only if you enable Virtual Shadow Maps or Lumen - both require TAA which is not acceptable for a lot of games). And I can’t think of any other way of having both static and dynamic lighting in a scene.