So I’ve run into a scenario that I’m a bit confused by. I was noticing some strange rendering costs in my scenes so I setup this test level to debug what was happening. It appears that UE4 is still rendering my dynamic lights even when they are out of view (behind the camera or behind a wall), so when my camera points in a direction that may have a number of lights in that direction I get massive performance loss. Even though I can only see 1 light in view, its actually hitting me with the costs of all the other lights that are hidden in that view.
I’ve attached screen shots to show how things are setup to test this. I setup a scenario that has lights behind a wall and a scenario where there are no lights behind the wall. When looking at the direction that has lights that should be occluded, you can see the FPS drops to 60. When looking in the direction that has no lights behind the wall, fps remains high at over 100. I also did a freezerender of each scenario to show what is happening. You can see the light positions thanks to the fog. (I tested deleting the fog from the scene to see if this was the issue but it still occured without the fog)
Does anyone have an idea why this occurs?