Debugging lightmass

Manually launching lightmass steps (allows placing breakpoints in lightmass, stepping through, etc)

  • Have a visual studio open to the UE4 solution, build lightmass in debug win64, set as startup project

  • Launch editor, enter the console command 'lightmassdebug'

  • Start a lighting build, watch the swarm log window until it says something like waiting for connection

  • Launch lightmass in debug, should complete the lighting build, and UE4 should import the results when it completes

Texel debugging steps

  • define ALLOW_LIGHTMAP_SAMPLE_DEBUGGING to 1 in both places

  • Disable lightmap compression with bCompressLightmaps=False in baselightmass.ini

  • Build lighting once with that in a map with static meshes

  • Hold T and select a texel on one of the built static meshes

  • Now launch lightmass manually as above, you should be able to hit breakpoints at the various 'bDebugThisTexel = true;' lines in lightmass

Reference From

Debug lightmass:

  1. Lightmassdebug command


  1. Build Lighting Only


  1. Launch Lightmass from visual studio manually in debug