In this post, I’m going to share with you a really cool trick with backface culling in Blender that produces a more natural, more realistic lighting for your scenes. I also think this trick works especially well with isometric rooms, which are really popular and a lot of fun to make.
Backface culling is not enabled in Blender by default, however by the end of this post, you will know exactly how to get it set up for your scene! (P.S. It’s really simple!)
Table of Contents
- What Backface Culling Can Do For Your Scene
- What is Backface Culling?
- How To Set Up Backface Culling
- Backface Culling in Solid Mode
- LookDev/Material Preview
- Rendered Mode (Cycles)
- An Easy Way To Remember How To Hook Up The Nodes
- Bonus Blender Lighting Tips!
What Backface Culling Can Do For Your Scene
Before we start getting into how to set up Blender backface culling, I want to show you the difference between actually using this trick, and not. The scene I’ll be using is a recreation of my own, personal living room.
Most isometric room scenes would have a couple of area lights off to the sides, giving the scene some nice, soft lighting. But for my scene, I chose to only have one sun light.
Since this is a recreation of my own living room, I wanted to stay as true to the real lighting setup as possible. As you can probably guess, we get a ton of natural light through those windows during the day!
The first picture is what this scene looks like without using the backface culling trick. The second picture is the exact same scene, but with backface culling. They are both rendered in Cycles.
It’s really hard to tell the difference when they are side by side like this. If you want to see a more dramatic comparison, watch the video above as I’m able to go back and forth between the two pictures through Photoshop layers. The difference between them is a lot more obvious.
The biggest takeaway though, is the warmness of the lighting. It looks so much warmer, cozier, and more inviting. Also, I think the couches look softer, instead of like bars of soap! The light and shadowing on the back wall is also a lot nicer with backface culling.
What is Backface Culling?
So what is backface culling? Basically, when you enable backface culling, you’re telling Blender that you want a particular face, or faces, to be one-sided instead of two-sided. By default, Blender is set up to show a texture on both sides of a plane, or face.
If you create a plane, you will see the default grey color load up on the front side of that plane. If you then rotate that plane to see the back side of it, you will still see the grey on the back side. That’s because every plane or face is two-sided. With backface culling, one of those sides will actually be transparent, or invisible.
This is great for isometric rooms because normally, we’re missing the front two walls and the ceiling of our room.
This means that whatever light we do have in our scene just floats off into open Blender space, never to be seen from again. With backface culling, we can bring those two walls and ceiling back, but have them be invisible to the camera. That way we can actually see inside the room like a normal isometric room, but have the other side act like a wall so that light can’t escape.
How To Set Up Backface Culling
To take advantage of this backface culling trick, there are 3 steps you have to do.
- Create a “shell” around your scene,
- Tell Blender what faces from that shell to be invisible,
- Enable backface culling.
The first step is to simply create an “outer shell” for your scene. This can be as easy as adding a new cube to your scene and scaling it to be the same size as your room. For my particular scene, since I have kind of a weird shaped room, I had to do a bit of editing in order to get it to be the same shape.
This step will depend entirely on the shape of your scene. Just make sure you completely engulf the room. Remember, you’re basically bringing back the missing walls and ceiling for your room if you have an isometric room scene. You don’t want any light leaking through cracks!
Next, while in Edit Mode, select the faces you want to be transparent, or invisible. Then in the Viewport Menu, go to Mesh > Normals > Flip. This will flip, or rotate the faces to now show the backside.
At this point, it will look like nothing has happened. But that’s just because we don’t have backface culling enabled yet!
Backface Culling in Solid Mode
Backface culling needs to be enabled for each “Viewport Shading” option (Solid, Look Dev/Material Preview, and Rendered) that you want to use. Even though it sounds like a pain to enable it for modes you may not use much like Solid or LookDev, it’s really not. It’s definitely worth doing in my opinion because they only take a few seconds to do.
For solid mode, just click the little dropdown menu next to the shader buttons. Go down to “Options” and select “Backface Culling”. That’s it! Now the faces you flipped earlier should be transparent! See? Wasn’t that quick and easy? 😂
Backface Culling in LookDev/Material Preview
Next, let’s go to “LookDev/Material Preview” mode.
When you switch into this mode, you’ll probably see a lot of black faces. To make them transparent, go to the Material options, scroll down to Settings, and click “Backface Culling”. Again, super easy to turn on in this mode!
Backface Culling in Rendered Mode (Cycles)
But Rendered mode is what we all actually want, right? 😂
If you want to do this backface culling trick in Eevee, you’re actually already done. Getting set up in Eevee is exactly the same as getting set up in LookDev/Material Preview. Just go to the Material options and select Backface Culling. However, if you want to do this in Cycles, you actually have to create a special material for it.
So with the material selected, go into the Shader Editor by clicking on the “Editor Type” button in the top left of the Viewport. This button is just above where it says “Object Mode”, or “Edit Mode”, depending on which mode you’re in. Then select “Shader Editor”.
If you don’t see anything here, make sure “Use Nodes” is checked.
From here we need to add 3 nodes.
Geometry, Transparent BSDF, and Mix Shader. You can quickly add these by pressing Shift A on your keyboard and clicking on the search function. Just start typing the name of the node you want, and select it from the list.
If you would rather find them through the menu, you can find Geometry in the “Input” menu, and the Transparent BSDF and the Mix Shader, both, in the “Shader” menu.
From here, connect the “Backfacing” output of Geometry into the “Fac” of the Mix Shader.
The “BSDF” output from the Principled BSDF (the default node in the shader editor) goes into the top “Shader” spot of the Mix Shader.
And the “BSDF” output of the Transparent BSDF goes into the bottom “Shader” spot of the Mix Shader.
Lastly, plug the “Shader” output of the Mix Shader into the “Surface” slot of the Material Output node.
I know that seems like a lot when you’re reading it, but once you do it a few times, it will be easy to remember.
An Easy Way To Remember How To Hook Up The Nodes
I used to struggle with remembering which BSDF went into which spot on the Mix Shader.
To be fair, I don’t think it really matters all that much because you can always swap them around if it’s wrong, or you can re-flip your faces. But it’s definitely better to get it right on the first try, right? So I came up with an easy way to remember the order. If you think about them in alphabetical order, it will be much easier to remember!
(G)eometry, (P)rincipled, (T)ransparent, goes right down the line on the Mix Shader!
Now with this alphabetical trick, you should have a much easier time hooking them up the right way!
Bonus Blender Lighting Tips!
That should now be everything you need in order to try out this backface culling trick in Blender for yourself! I will just leave you with two more bits of advice before we go.
First, is that you may need to be creative with placing some extra walls in your scene if the light isn’t working the way you want. Sometimes, your “shell” just isn’t enough.
For example, sometimes you need to place an extra wall to the side, or above your scene to block out unwanted light. But since you don’t want those walls to be visible, this is where the backface culling comes in.
Second, the lighting doesn’t always react the same way in a blocked off room with backface culling as it would in a completely open room. Remember, we’re trapping light inside our scene instead of just letting it escape into open space!
Sometimes that means you’ll need to lower the strength of your light because it’s now blasting your scene from being trapped inside. Other times, like in my living room scene, I had to greatly increase the lighting strength.
In my original scene without backface culling, I had my sun light set to a strength of 8. As you can see from the picture below, a strength of 8 was not going to cut it for this new backface culling version.
So I just kept increasing the strength until I finally landed on 45. It seems like a lot, but it’s what this particular scene needed. I probably could have even kept going!
So just keep that in mind as you’re experimenting with your lighting. You may have to dramatically lower or raise the strength of your lighting to get the look you’re going for.
I hope that helps, Enjoy!