System Lightgrid?

[AngelModder]

Ok, well this is one of those moments where I completely admit I don't know some thing and ask. I really think this is one of those things that is assumed most know or not I am unsure but there is like jack **** about it really. However in some sample maps (the good ones) they often use "System/lightgrid" around their main play areas. 
What is it? What do you do with it? 

[mrwonko]

The lightgrid is a 3D grid throughout the map that stores the light brightness/color/direction at each grid point, which is used for dynamic lighting e.g. on first person weapons. I suspect you can use the system/lightgrid shader to define the extents of that grid, but I don't know for sure.

[AngelModder]

16 minutes ago, mrwonko said:

The lightgrid is a 3D grid throughout the map that stores the light brightness/color/direction at each grid point, which is used for dynamic lighting e.g. on first person weapons. I suspect you can use the system/lightgrid shader to define the extents of that grid, but I don't know for sure.

Yea that's what I can't seem to really find any explanation of, the application/cautions etc of using system/lightgrid. From best I can tell in this sample map he used it say around the main platform you duel, but then the other 90% that's just visual background candy is left uncovered. However said eye candy area's are still physically reachable by the player. 
I am considering that perhaps it is a way to distinguish to the engine that "here are important areas" focus on these first and upmost. Sort of like a top priority listing for the lightmapping.

Where is Darth G when I need him XD

 

[AngelModder]

So after some more digging and referring more to quake3 rather Jedi Academy specifically. I found this "Lightgrid is used when you want to restrict the size of the lightgrid to certain boundaries for performance optimization. Take a space map for example, you may not need lightgrid calculations done in the void where you have no light sources anyway so you would circle a single lightgrid brush around the region that you do want lightgrid to be calculated. - Obsidian on  quake3world.com" 

Seems like an anti-Lightgrid would be more useful. I'd prefer to mark areas I "dont" want lightmap calculations. *Shrugs*

So wow this little bugger. I need to write up a tut on this, I'm really suprised we don't have one. THIS is amazing. I need to test it's doo's and don'ts just yet. But using this I was able to engulf my main jh3 area in system/lightgrid. Then made another box the exact size of the map limits X/Y/Z as my map moved it up textured it as my sky, leaving it without the lightgrid. therefore telling the engine in this area don't waste bsp space/time on doing light work skip this. - To my suprise it worked, the lightmap compile was in no way effected by the introduction of a huge flight area. 
The biggest death of 90% of space mods was the vis/light compile. Vis I've got handled - as long as you know what you're doing it can be achieved, but the lightmap compile would always break out backs/pc limits. Problem solved.

[SomaZ]

@AngelModder I'm currently writing a tutorial series regarding precomputed lighting in id tech 3. Lightgrid is also part of it ofc. I do this to educate people to use my blender addon for baking new lighting in blender instead of using q3map2. If you have questions regarding lighting right now, you can ask me on discord.