Epic Games' Technical Artist Zeshi Chen shared an alternative approach to creating a fake opaque material in UE5, inspired by the artist's work on Fortnite.
In game development, we often run into a common problem: we want an object to look semi-transparent, but we don't want to use real transparency. This is especially true for environmental assets, where heavy use of transparent materials can be a performance disaster.
I've created many different “fake transparency” setups over time, and here I'd like to share a simple, universal approach that doesn't rely on any advanced techniques. The core idea is to reduce the Base Color, then layer various computed values into the Emissive channel to create the illusion of translucency.
Base color
Emissive
First, we can use a Phong model together with a normal map to generate basic light and dark areas, as well as the primary specular highlight. By adjusting the brightness of the dark side, we can mimic a sense of fake transparency. Tweaking the highlight creates the illusion of different roughness levels. This forms the first layer of our emissive value setup.
Phong lit
Phong specular
Next, we can build a second layer of emissive on top. In this case, I wanted to create the look of cracks and fibrous inclusions inside a crystal. There are many ways to achieve a sense of depth, but here I'm using a simple BumpOffset, which is easy for anyone to implement. Of course, you can use more suitable – or more expensive – methods depending on your needs.
Second Layer Noise
At the same time, we apply a BumpOffset to the crack normal map as well and introduce some variation to the BumpOffset depth to keep the effect from looking too uniform.
Second layer normal (tangent space)
Next, we use the second-layer normal to generate another round of specular highlights. We then mask out any highlights that fall outside the crack regions and blend the remaining highlights together with the second-layer noise.
Second layer Specular
To make the crystal appear more translucent, we use both the first-layer and second-layer normals to perform two refraction calculations. These give us a world-space vector to sample the sky, forming the third layer of our emissive effect. Of course, if your target platform is mobile, you can replace this with a solid color blended through various dot-product operations. You'll lose a bit of detail, but the overall look will still hold up. You can also adjust the intensity of this emissive layer to control how transparent the crystal appears.
Sky light env sample
Finally, I added a fake transmission effect driven by the scene's directional light vector to simulate the crystal being illuminated when facing the light source. This layer is blended with the colors and noise from the previous stages to represent internal impurities. This step is entirely optional, especially for indoor scenes or crystal clusters – where you can simply disable or reduce this emissive layer if it doesn't fit the look.
Fake Transmission
This is the overall approach. Since each layer is fully controllable, artists can freely adjust the effect to suit their needs or push it toward various stylized looks.
Thank you for reading.