JUAN GOMEZ: Hi, my name is Juan Gomez from Epic Games.
Today, I'm going to be covering how to do interactive lighting on an LED
wall.
So this technique could be really useful for in-camera VFX production,
where you have creative director DP looking at the wall on set,
and they want to make changes to the lighting that is on the wall.
Most of the time, they want to see the changes through the camera.
So this is exactly how I'm going to describe how to approach this.
What we are seeing currently in front of the camera
is a super simple scene that I set up so we can quickly
explain a couple of these concepts.
It's a GPU light bake that I did previously.
But let's say the creator is going to come and ask me,
you know what, I'm going to move the direction of the light.
We want to make it a little bit warm.
And we're going to do some changes.
But they want to see it through camera.
So the first thing that, most likely, you want to do,
is just, yeah, let me rotate the directional light.
But the moment I rotate it, as you can see in the editor
and on the wall, I still have the previous light bake.
So it can be really confusing, like OK, which one is the new one?
It's definitely not the desirable effect that you want to do.
So I want to turn on ray tracing, real time ray
tracing, just to give a preview of what it could
look like if we do a GPU light bake.
Real time ray tracing, especially real time GI,
can be really expensive for the GPU.
So most likely, it's not going to give you
a good performance on LED wall.
But you just light bake it, it's not going
to have much of a cost, or no cost.
So how are we going to get rid of the previous light bake?
So the way we do this is by going in and we go into World Settings.
And then in the World Settings under Lightmass settings,
we check for Force No Precomputed Lighting.
What this is going to do is going to clear the previous light bake.
So we're going to go in build option, build light only.
So this is going to get rid of the light bake in my editor box.
But I still have it in the LED wall.
So what we need to do, we need to push these changes
through multi-user to the LED wall.
And the way we do that is by saving.
You can click Save All.
Saving all the levels that currently have light bake information,
most likely is the build data, what we need to save.
So as you can see, I have all these levels that they do have geometry.
And they do have light bake information.
And I'm just going to go in ahead and hit Save.
What is this doing, is just going to sending
this information to the wall.
So you can see now on the wall, we have exactly
what I see in the editor.
It's a couple of things that I want to double check.
It almost look like, on the wall, I have SSGI on.
So let me take a look.
SSGI, see if this is enabled.
It is not enabled, which is good.
I don't want SSGI.
I want to be more accurate.
So what I'm going to do next, I'm going to check,
in my post process volume, I want to check what kind of ray
tracing I have enabled.
So in this case, I have ray tracing global emission disabled.
So now, the minute I'm going to enable this, I can use Final Gather,
as you can see.
It give me a close approximation.
Brute Force is definitely a much accurate GI solution,
because you can actually increase the number of bounces.
And as you increase more bounces, the more accurate it gets.
So right now, I'm going to increase it to two bounces.
I see the results on the wall similar to what I see here in editor,
so that's good.
Now, when I go in and change my directional light,
I can get some sort of preview of what it's going to look like.
So in this case, let's make it a bit warm.
And as you can see, I'm getting a preview
of how this room is going to get the global emission
through the light rays, the sun rays that
are coming through those two gaps.
So this is good.
This is good, because then, at least your DP's
are going to get a little sense of how much fill light you're going
to get through the global emission, because remember,
what we're going to do at the end, we're going to do a light bake.
But keep in mind, ray tracing and GPU light
bake, use completely two different approaches,
two different algorithms.
GPU light bake uses path tracer.
Ray tracing, it has its own technique just to go, to make it faster.
So there is never going to be an apples to apples comparison.
But these, at least, give you a good preview.
Another thing that is really nice when you're doing real time
ray tracing preview is that I can go in,
and we can talk, for example, like the DP can say,
you know what, I want this to be a clear day.
So you can actually adjust.
As you can see, I can adjust the source angle.
And I can see, now, a much, much crisper
light coming through the holes.
Or if you say, you know what, it's supposed to be overcast.
Let's see how that goes.
So you can actually start softening your shadows,
start softening the shadows, so then you can start getting the sense of,
yeah, it's a bit overcast, not such a clear day.
This is stuff that you can not preview without ray tracing.
So let's say we are happy with this.
And the next step, it will be just do a light bake.
So in this case, I'm going to go and go into my GPU, light bake.
And I'm going to--
these are decent settings for now.
Just going to get something quick.
And I'm going to turn off real time previews, so it goes much faster.
And then I'm going to click Build Lighting.
So right now, it's building in the background.
It's going to-- all this processing is happening
in editor box, my local machine.
This process is not yet on the wall.
So after this is done, I'm going to do the same technique
that I did before, which is disable and save the build data.
And that's going to get sent to the wall.
And one thing that I probably forgot was the World Settings,
uncheck this.
OK, so now, I see the light bake finish.
It looks nice, kind of close to what I wanted.
The next thing you want to do is go in and, once again,
do a Save All, because obviously, as you can see now on the wall,
it's not the exact same result.
But we go in here.
And before I do that, sorry, I'm going to turn off
ray tracing so it doesn't add--
doesn't double up the--
here we go.
So disable it, perfect.
So now, in my editor box, this is completely
the results of the GPU light bake.
And now I'm going to save this on the wall.
Saved in, Save Selected.
So now I save it locally.
It's now sending the information to the wall.
And now we can see the results on the wall.
Right now, the mipmaps are getting loaded.
And now we see it.
So as you can see, I was able just to first do
a preview using real time GI.
That gave me a little bit of sense of what it's going to look like.
And now, when everybody's happy, then I light bake.
And I push it to the wall.
Thank you so much.