Sprite-based decals have dark grey edges with Ambient Occlusion enabledDescription
Pictures and description posted in this thread: viewtopic.php?f=50&t=56039
Decals that use sprite graphics have a dark grey edge to them. This appeared some time between GZDoom 2.2.0 and 2.3.2.Steps To Reproduce
Fire the plasma gun at a wall and look at the decals. Some mods can be used for even more obvious examples. e.g. my Burghead mod.
See the linked ZDoom thread for pictures: viewtopic.php?f=50&t=56039