Question Faces of objects light up as if they emit light themselves...

I have a very weird problem. I made a few very simple objects using ProBuilder (plinths). They have a simple wood material and using the URP/Baked Lit shader. It's also marked as a static object.

After I have generated the lighting, some of the faces light up as if they are emitting light themselves. Weird thing is, the entire scene is lit by a single point light, with its mode set to Baked. Even stranger, the plinth is outside of the reach of the light. Not only is the plinth further away than the light's range, The front of the plinth (facing the light) is completely dark, there are items between the plinth and the light, and the faces that are lit up are on the backside of the plinth. And yet they light up. I've tried everything I could think of but nothing seems to help. I even tried other objects and they experience the same problem, but only in that position. If I look at the lightmap, I don't see why the backside should light up, so it's not information in the lightmap.

If I disable the (one and only) light, it doesn't light up, so it is cause by the light.

One thing I noticed: When baking light, the (back faces of the) plinth stays dark till the very last second of baking. They only light up when the lightmap is created.

Before baking light (you can see the light in the background):



After baking light:



This is the backside of the plinth, which is actually inside a wall.

Also, the entire backside of the plinth is lit evenly:



What could be causing this? The problem disappears if I set the Directional Mode (Lighting) to Non-Directional.

 

2021.3.19f1

Here's another example of a piece of geometry that lights up as if it's emitting light itself. It's not a single face that's lighting up, it's actually part of a face.

No baking done yet, lighting comes from Scene View Camera Light:



After baking (yes, it's a very dark scene):



The light map (which doesn't show any problems):



Texel Validity (which shows problems, but no ideay what's causing them. These are very simple geometric shapes):



UV Overlap (again, shows problems but no idea how to solve them):



Now even though there are invalid Texels and overlapping UVs, I'm not sure those are causing the problem since these problems are everywhere and the problem doesn't show up immediately after I create/place the object. It will be fine and then much later in the project, it will suddenly show up. Also, there are numerous duplicates of the object, and none show this problem except this one.

(continued in next post)

 

But if you look at the Directional map, the problem becomes quite obvious:



Again, no clue what caused this error or how to prevent it.

 

I would like to add that it only seems to happen with geometry which I have stretched out by moving the vertices instead of resizing. Let me try to explain with the above object as example.

First thing I did was create a simple cube (ProBuilder):



I then bevel the edges:



Now I want to stretch this, but if I use the resize tool, it will deform the bevels:



So what I do is simply move the vertices on one side:



And this is apparently what is causing the problem. Because I've noticed that when I stretch an obect by resizing over a single axis, there are no problems. But if I stretch it by moving vertices, all kinds of problems occur.

 

One more example. Here is a white plinth. It's not scaled (yet). No baking, Scene View Camera Light:



After baking:



Now the reason I want to stretch it, is because if I simply place multiple instances end to end, each instance gets lit differently:



This is how it looks if I stretch it by moving the vertices on one end. As you can see, it's lit completely wrong:



The only way to get it to be correctly lit, is by sizing it over a single axis:



(There's actually another light at the far end causing the end to become a bit lighter again)

So there you have it. I'm not sure this is a bug, or a wrong setting, or me just being an ID-ten-T.

 

The problem seems completely random. After baking the lights for above example, I had a look at the problem area of the first example and it was gone (don't have a screenshot of that, but imagine the object of my first message lit correctly). I then removed the sample object (the white plinth in above post), rebaked the lights and the problem returned. So apparently, adding a random object somewhere in the scene causes the problem to appear somewhere else.

 

Increasing the Lightmap Padding from 2 to 3, seemed to have had a positive effect. I don't know yet if it completely solved the problems, have to do some more testing for that. But a definite improvement!

 

Flipped/Incorrect Normals.

 

I'll check the double-sided GI in a minute but just wanted to say there's no "Backface Tolerance" option.

 

Enabling Double-Sided GI did not make (much of) a difference. The problems are still there, they just moved to other objects (so objects that were lit incorrectly are now lit correctly, but now other objects are lit incorrectly).

 

Ah ok. But if I click "View", everything is grayed out - cannot change anything.

 

The default Lightmap Param Assets are part of the URP-package, and thus not editable. Create a new one, and use that.

 

Just for the heck of it, I increased Lightmap Padding to 10. That seemed to get rid of all overly lit objects. But still objects are incorrectly lit. For instance, here is a piece of a wall that is lit correctly:



The frames, lamp and light have been duplicated and moved a few meters to the right on the same wall. But now, it's lit completely wrong:



Exact same objects, exact same orientation...

 

Sorry, my last message was incomplete. In the first image, the frames are dynamic objects (to see how it should be lit). In the second image, the frames are marked as static (and thus get their lighting from the lightmap)

 

The problem is not in the light map. I've set lightmap padding to 6 and still I get this:



Looking at the object in the lightmap, I see no bleeding or anything:



The Directional map however, does show a problem (again):

 

I've increased the Backface Tolerance from 0.9 to 1 (the max). Made no difference.

 

Interesting observation: Switching from the Progressive GPU lightmapper to the Progressive CPU lightmapper and the problem disappears...

 

Oh man, this is frustrating... It seems that with every bake, quality of the lighting gets worse and worse.

Now I noticed my skybox has disappeared (it should be a nice night sky instead of the blueish whatever it is now, and these dark lines have appeared.



No matter what I change the skybox to, it stays blue and I can't get rid of the dark lines either...

 

Skybox is back - something caused this to be "off", even though it was showing "on".



And the dark lines were caused by the shader rendering both sides. Which still shouldn't happen but I could get rid of it by only rendering the front. Still other lighting problems which aren't caused (or solved) by anything in the above posts. Now, instead of spots emitting light, I have dark spots which are not shadows and any of the above solutions does not get rid of it.



I think this is caused by bleeding in the light map. The reason why increasing the lightmap padding does not work is because that increases the distance between objects in the lightmap, not between the individual parts of an object.