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Light & lightmass


First I am sorry if I did mistakes I am not english.

I would like to do a big world (the idea is to use world composition but it is not working for the moment, never mind it is not the question of the day...). I read A LOT of things about lighting a map. And since I am not good in english, words that are use in tutorials are too complicated for me... So how I do light in my level is quite bad (I think ?) - I add sky light & directionnal light linked to the sky. I increase intensity a lot to have not weird dark shadow - I add MANY point light & spots in my house to have a nice light (for example in a really little house of 800x900 units, I have 26 lights, isn't it too much ?

And I never added Lightmass.... And when I build light it take a lot of time (normal) and say something about lightmass important volume and UVs... I don't understand a word of all this things. What is the difference between lightmass character indirect detail volume, Lightmass importance volume and lightmass portal ? And how do I add them ? I know were to find them but I don't know how to place them well. Do I need to place it at the middle of my world and then increase the box size to make it wrap my world ?

My question seems to be easy and I know there are a lot of subject about it but I am really lost and I am not able to understand unreal documentation. So please can you explain me one more time with easy words ?

Thank you in advance

Kind regards !

Product Version: UE 4.20
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asked Oct 23 '18 at 04:12 PM in Rendering

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5 answers: sort voted first

Hi there,

here are some very simplified explanations to get you started:

Lightmass Importance Volume:

(Lightmass is the system inside UE that calculates baked lighting (lights set to "static" or "stationary")
(Other option is dynamic lighting (lights set to "movable" and but also to "stationary". "stationary" lights can create dynamic direct lighting, but baked indirect lighting.))

  • lightmass importance volume is only relevant when you use Lightmass (Lightmass = baked lighting = lights set to "static" or "stationary")

  • the lightmass importance volume defines the area in which Lightmass should create higher quality indirect lighting. If you don't use one, everything will only receive low quality indirect lighting.

  • so: put a lightmass importance volume around areas in which baked indirect lighting should have good quality. Around the house for example, a little bigger than the house.

  • BUT: if you put one around the whole large world it will take VERY long to build lighting and the lighting data will become very large. Normally for large worlds baked lighting is not used for those reasons.

  • you can use more than one lightmass importance volume, e.g. 3 houses = 3 volumes

  • it also defines the area in which a moving object (e.g. the character) will receive more realistic indirect lighting.

    Lightmass Character Indirect Detail Volume:

  • similar to the lightmass importance volume: it defines an area in which a character will receive more detailed indirect lighting, but this time the character will receive more detailed indirect lighting EVERYWHERE in the volume. In the lightmass importance volume the more detailed indirect lighting is concentrated to areas above the floor, not in the air

  • use this in spaces in which a moving object should have more detailed indirect lighting everywhere, not just above the floor (e.g. if a character should fly through a large closed room or something)

  • make the box the same size as the space in which you want better indirect lighting

  • you can use more than one volume

    lightmass portal

  • only relevant when you use Lightmass and want to light a space with small openings from the outside (e.g. a house with windows)

  • put one into any opening through which light will pass, such as windows, open doors, cave entrances. One portal for each opening

  • make it about as large as the opening

  • it does not have a front/back so the direction is not important

  • the effect for the baked lighting is very small, you may not see a difference LightmassPortal

Hope this helps a little.

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answered Oct 23 '18 at 05:03 PM

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Thank you very much for your answer ! Thanks to you I finally understand the goal of lightmass !

So I added lightmass in my house. But what is the purpose of the "Lightmass Character Indirect Detail Volume" ? Since I have placed my lightmass in my house there are no other place that can be good to place Lightmass Character Indirect Detail Volume no ? And another question, you said the Lightmass Character Indirect Detail Volume offers more detailed indirect lighting everywhere in the volume, and lightmass volume do it only above the floor, but if my character is on the floor, he is tall so will his face be impacted by it or not ?

Another question again (sorry), for lightmass portal you said that the effect for the baked lighting is very small so I may not see a difference. Does it means that adding one is not necessary ? Does it means that I will no see with my eyes the difference if I have or not the lightmass portal ? I am not sure of what you would like to say about it ?

A little example of how I placed my lightmass volume : alt text

And last question (that have nothing to do with the subject), I would like to mark your answer but I am no more able to do it... If I click on the arrow on the left then it display "Request method not allowed". alt text

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answered Oct 23 '18 at 07:53 PM

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The lightmass importance volume will provide indirect lighting information for moving objects above surfaces (e.g. floor) up to 300 units above the surface, so the head of a character will be included :-)

I have not used a "Lightmass Character Indirect Detail Volume" myself before, but I think you could use it like this: in a large house with an elevator you can use the lightmass importance volume to cover the whole house and then a Lightmass Character Indirect Detail Volume for the elevator shaft (so it's also inside the lightmass importance volume) because higher up in the elevator shaft the lightmass importance volume will not give indirect lighting information (because it so more than 300 units above the bottom floor) but the Lightmass Character Indirect Detail Volume will.

The lightmass portals will help if you want very high quality indirect lighting with very detailed shadows, and they will also bring a little more light into the interior. In general, they will bring more photons into the interior and more photons means more light and more details.
You could set up a small test map with only the house and some objects inside (a chair and table maybe) and then do one bake with lightmass portals and one without. After each bake, switch to "lighting only" view mode (alt + 6 in the editor or click here:
alt text
and take screenshots from fixed view angles for each version. Then compare the screenshots to see the difference.
(You can set fixed view points in the editor window with "ctrl + 1" "ctrl + 2" .... and then jump back to those views by just pushing "1" "2" ... So move to a good view, hit "ctrl + 1", then move to another view and hit "1" and you will be back at the first view.)

One complication in this context: You will see the difference better if the objects inside the house use a higher lightmap resolution, meaning that they can show more detailed shadows. Lightmaps is a whole topic for itself, but for this test you could select the interior walls, the floor, the chair and the table and set their Light Map Resolution to 1024 inside the "Details" window:
alt text Then do the bakes. But remember: Higher Lightmap Resolutions (1024 is quite high) means longer bake times and larger lighting information, so it will be too much to set everything in your large world to 2014. It's always a compromise between performance and quality.

Take a look at these two training streams, they explain lighting in much more detail. Start with the first one, it begins with lightmass importance volumes :-).

baked lighting:

dynamic lighting:

Where did you get the trees in the background? The scene looks quite nice already.

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answered Oct 24 '18 at 07:47 AM

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Thank you for your help ! I will watched the tutorial you gave me.

My game will be a multiplayer game so I think the quality of the light must not be too high for performance isn't it ?

The tree on the right come from LandscapeAutoMaterial and all other trees behind the house come from UltimateRiverTools :)

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answered Oct 24 '18 at 09:32 AM

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avatar image benhkvr Oct 24 '18 at 09:50 AM

Thanks for the info.

In a multiplayer game each client will be handling the map (including lighting) individually, so this is not network relevant. It just depends on the processing power of the client. Only the information about the "action" of the game will be replicated over the network, like character movement, spawning/destroying actors, player information etc.
If your Multiplayer game includes changes of the lighting during game play then only the information that the change should happen would be sent over the network, but each client will load/adjust the new lighting locally. Of course this does not mean that you can bake lighting during gameplay, you can only load pre-baked lighting scenarios or change dynamic lighting during game play.

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Ah thank you for the info ! I think I will leave the light to a good quality (but not to high for the moment) and when I will have finish the game I will try to increase the quality depending of how much process it takes to run the game (graphism etc...)

Thank you for your help ! How can I mark this question as resolved ?

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answered Oct 25 '18 at 07:20 AM

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avatar image benhkvr Oct 25 '18 at 07:33 AM

You need to click the arrow on the left :'-(
I can't do that for my own post and if it does not work when you try we are finished.
Much success and until next time!

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