Material Ambient Occlusion in Unreal Engine 5

I'm going to jump straight into a setting you should probably have set up right now.

In your Unreal Engine 5 project settings, search for Allow Static Lighting and uncheck this box.

That will now enable Material Ambient Occlusion, which will allow us to go from this result to this.

Much cleaner and improved shadowing in indirectly lit areas. You're welcome.

If you've been using Lumen in Unreal Engine 5 for a while, you might have noticed that it is missing the ability

to control ambient occlusion. And while we used to be able to control AO through the post-process volume in Unreal Engine 4, things are different now.

Now right before we jump into how and why this all works, and a bit of a shameless plug, this video is sponsored by me.

In December I released a new tool called Easy Mapper on the Epic Marketplace, which is now 50% off for the next week.

Easy Mapper is a master material setup that supports World Alliance triplanar texture

projection combined with nanite tessellation and displacement, and advanced vertex blending all in one elegant package for easy texture blending on all of your assets.

I also just released an update for EasyMapper allowing custom grayscale maps and the ability to paint puddles.

So if you've been on the fence, now is the time to get it because it is dirt cheap. You'll find the link down below.

Okay, so let's dive into why Material AO is important.

Light occlusion, or AO for short, is a rendering technique used to simulate the soft shadows that occur in creases, cracks, and corners of objects where light is occluded by nearby geometry or models or whatever.

Screen Space AO was a very popular feature in UE4, and a lot of people are wondering why it can't be used anymore with Lumen.

In Unreal Engine 5, however, Lumen uses a technique called global illumination, or GI, for its lighting.

GI is all about direct and indirect lighting in a scene, including effects like proper color bleeding and reflected lighting and shadows from multiple light bounces.

Unlike ambient occlusion, global illumination does take into account the interactions of light with surfaces and materials.

AO only takes the proximity of Geo into account, not the lighting.

So even if a surface is brightly lit, AO still shows up and looks a little fake and gamey.

AO and GI are two totally different rendering approaches.

So with Lumen, a screen space AO isn't really necessary anymore because GI takes care of the ambient shadows for us already.

Having SSAO and GI would result in shadows that are way too dark, and it just doesn't look very good.

But Lumen isn't perfect. In order for Unreal to run in real-time, shortcuts need to be made somewhere.

And Lumen takes those shortcuts by sacrificing lighting quality, and more specifically, lighting accuracy.

Because while Lumen does use ray tracing, it only calculates about half a ray per pixel, while path trace renders need about 200 plus rays per pixel for acceptably noise-free GI.

So yeah, shortcuts need to be made somewhere. There's no free lunch. While Lumen does take care of the general shadowing between objects, in fact, it's really good as of Unreal Engine 5.3.

I've got to give credit where credit is due. But it just isn't accurate enough to get those really satisfying high-frequency detail shadows that you get when you compare it with the path tracer.

Take a look at this render I made in a video last year. The path trace results are simply better, especially once you know what to look for.

Fortunately, that is where Material AO can come in very handy, which is the feature we just enabled by disabling that checkbox at the beginning of the video.

Don't ask. So here I have this awesome suit of armor model.

You'll see that the armor bits do get a bit of self-shadowing thanks to GI and Lumen. You get this for free.

But some of those contact shadows still feel a little bit floaty.

Like this part here, for example, right in between the two metal plates, it should be very dark.

Not much light should be able to reach in there. If we compare to the path tracer, you'll see that the path trace results just feel more better.

The pieces of armor feel more connected. Right here, again, if we zoom in to those thinner placed metal, the contact shadows here are just so soft and accurate and crisp.

It is all about those contact shadows. But, using material AO, we can partly make up for that lack of accuracy when using Lumen.

So using an AO map for this model, by plugging the map into the ambient occlusion slot of the material, we can go from this to this.

It is a huge difference, but the really cool thing is that if I rotate the light around, you'll notice that the AO we added fades away.

It only shows up in indirectly lit areas of your models.

It isn't just multiplying the AO on top of the base color like that old school thing we used to do back in 2008.

This is great because you wouldn't want a dark AO shadow to show up when a big bright light is shining directly on it, right?