Avoiding the Blackhole

[Snejk]

I bet everyone's had enough of the "black hole" lightmap glitch. You just keep updating your map more and more, then 'poof'! - Half of your precious polygons are GONE - they're there, but painted pitch-black despite the big lamp above them. You caulk like crazy to keep it away, but it comes back and frustrates you again. Well, not anymore...
As long as you manage to avoid the glitches that cause it, of course.

As most know, a lightmap is a bitmap painted on the polygons to make them bright or dark in correct places. GZMap doesn't generate it, FSRad does. GZM sends FR info about polygons and light spots, then FR returns a bitmap which is converted nicely and put in the map by GZM.
So, why the black holes?

It's not that obvious, but the GZMap is at fault. FR can't export too big bitmaps - it splits them into a few bitmaps instead. That's where the problem appears - GZMap doesn't handle multiple bitmaps properly.

I don't know which line of source code is screwed up, or what is the limit of bitmap files GZM can handle properly, but I know one thing - GZMap screws up the order of lightmap files if there's too many of them. So, the key to a proper lightmap is SURFACE. You should discard everything you can't see by caulk - because it decreases the amount of lightmap texels to be used on the file. But remember - don't discard faces you can't see, but light can. Caulk does NOT block light - that's the cause of missing shadows that should be casted by some ceiling elements you usually remove the top faces of. Also, if you use radiosity( -light instead of -fastlight, recommended for maps with sunlight or dark corners) light will bounce off objects - also those you don't necessarily see but light rays do reach and it does influence the final result.

I figured that my maps never have blackholes when the lightmap fits into one BMP. How do I know it? Well... I opened GZMap in a hex editor, and enabled the -writebmp 1 key on FSRad.exe call. That way I can see without testing if the lightmap is too bright, too dark, or maybe there's more than one file making it possible to screw up.

So, how to decrease the surface used? For low detailed or terrain maps, you should decrease the lightmap resolution at the FSRad settings(just open the exe itself). Also, as I said before - caulk surfaces that won't ever see the light of day. Also try to make maps relatively small, with sometimes more geometry than flat surfaces(a very large grating seen from afar should be actually a brushmodel with discarded faces, not an alpha texture).

And on the file limit... I think that if it generates 0.bmp and 1.bmp it's still okay. But don't exceed that number, as it might screw up later.

UPDATE:
I checked on something lately... The two things that help might be increasing lightmap resolution, and lowering the per texel ratio.

[ManyBlackPpl]

great tut man, this is gonna help out alot of people who have problems with lightmapping. I just hope a fix for this will be issued soon, cuz it's more fun to play in a bigger map, rather than a small one.

[Snejk]

It won't be fixed by Legion, that's for sure. I guess I'll have to look into the source myself.

[ManyBlackPpl]

dude, if you manage to fix that, you'd be crowned king on the forums..........well not really, but alot of people would definitely be really grateful . Btw, what are you using to look at the source code and what not?

[Snejk]

I just download source from the project page and open it up with Dev-C++ to look for mistakes. No idea where might the bug be so far.

[ManyBlackPpl]

ah ic. Well Good luck man, I think you're gonna need it (not saying your noob).

[DusteR]

thankss I hope you can solve this bug! ^^

[Snejk]

I really doubt it, since even if I am a coder, I don't know the source enough to even know where to look.

[HellSniper]

ihave the opposite lol
I have Whiteholes (no kidding).

[ManyBlackPpl]

loool! Well I'm assuming it's the same problem, except the situation is reversed. :O. Heh, idk

[DusteR]

but you can see the texture true the white, so I guess the white version of the bug is better ..

[Snejk]

The black(white?)hole is a part of the lightmap simply misplaced, so how it looks doesn't really matter.

[ManyBlackPpl]

The black(white?)hole is a part of the lightmap simply misplaced, so how it looks doesn't really matter.

wait, so are you saying that the white part of the map turned out properly, and all the black stuff around it was the black hole? O_o. Dam....

[Snejk]

No, I mean it was supposed to be dark but a bright part of the lightmap was misplaced and put there. It's probably pitch-black in the place where this part was supposed to be.

[HellSniper]

I got no Black spots on my maps, all i get are those white spots .-.