Very long (maybe infinite) lighting build times on empty or very small scenes

Hello everyone. I just discovered an issue in 4.9.1 that didn’t happen in 4.8.3. These are the reproduction steps:

  • Create a new project.
  • Create a new Empty level.
  • Hit the build button.

The lighting build process will never end or it will be very long. Now let’s do the following:

  • Add a cube to the scene to location 0,0,0. I use the one called Cube in /Engine/BasicShapes
  • Hit the build button.

The same will happen. Infinite building times. Now one more thing:

  • Scale the Cube to 2,2,2.
  • Hit the build button.

Now it builds the level instantly as expected.

It seems there’s a problem with very small or empty scenes or something. I tried with 4.8.3 and I didn’t have this issue. In 4.9.1, I also tried with different lights, movable, stationary, adding a Lightmass Importance Volume, etc. But it always takes too long to build the level if there is no content or it is very small. The same happens by adding a BSP cube. With the default 200x200x200 cube, the scene builds fine. Setting it to 100x100x100 it has the same problem again.

Greetings!

Hi PacoChan,

This is a known issue that is already reported with UE-20782.

Thank you for taking the time to post a detailed report. These are always very helpful and much appreciated! :slight_smile:

Tim