[UE5] Efficient way of getting mesh's cross section as a mask


I’m working on a shader for a bottle containing liquid in Unreal Engine 5. I’m currently having trouble masking the bounds of the liquid’s surface based on the shape of the mesh (cross-section at the liquid level).

For now, my mesh is opaque and in default lit mode, and I’m faking the reflection/transparency of the liquid. To create the liquid surface, I drew a horizontal infinite plane at the liquid level (following left image).

What I’d like to do is crop this plane according to the mesh’s bounds, as shown here (random-looking bottle cross-section).

I need a way to get a mask containing the cross-section of the container mesh (square bottle, cylindrical bottle) at the liquid level (like the green flat part in the right image, but as a mask).

But the problem is that I can’t use depthFade (I’d like to have everything inside one material, so no slicing with a plane and using a depthFade). I’ve also tried to use a render target, but I don’t believe it’s the best solution because I would have trouble rendering multiple bottles at the same time, and I have more than just the cross-section.

I’ve also thought about using signed distance fields to mask my plane. This would involve converting it to world coordinates and culling based on the value of the signed distance field of the mesh bounds (I believe that if the distance field < 0 then it is inside ?), but I’m having trouble figuring that out.

I’m fairly new to shaders, so any advice would be nice :slight_smile:.

Thanks in advance.


Hi Yadon,

  1. I think this is using a closed container, and its Unity, but might be of help.
    What looks like the surface plane are actually the backfaces of the container:
    Liquid Shader Breakdown | Unity URP + Built-in - YouTube

  2. Using Blueprints:
    You could also use 2 line traces to get the elipse radius of the pour direction and the orthogonal radius, and scale the (round) surface plane depending on that. Helpful for an open container if you want to determine if fluid is spilled or not. Needs additional material logic to make it look okay.

  3. According to Suggested Topics there was a recent discussion about methods:
    Try to recreate this effect with unreal material

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I don’t know if this helps. I made a simple water bottle shader a few months ago for fun, and this material function is the main method for the shader. After getting the mask I made this shader with a masked unlit material double-sided.

Animated it with sine function on z-axis world space that can be controlled by blueprint based on actor orientation.



The topic link (3rd point) was the way to go, thanks !

I ended up using a signed distance field and clamping my plane according to the distance field’s value, which allowed me to render only the cross section.

However, if anyone comes across this in the future, I think it’s worth mentioning that mesh distance fields have been disabled on Intel graphics cards.

“All Mesh Distance Field features have been disabled on Intel cards because the HD 4000 hangs in the RHICreateTexture3D call to allocate the large atlas.”

source (hardware limitations): Mesh Distance Fields in Unreal Engine | Unreal Engine 5.0 Documentation


Hey Yadon, this looks great. I got to try this method too!

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Would love a tutorial on this since the only ones I find are Unity!

I provided you with the files, there are two simple materials, one texture, and one blueprint actor. Just hook up the texture in the material, and the materials to the actor and you should see this result.


The project is made in Unreal 5.1.
Thinker a little bit with the materials and you will see they are extremely easy to grasp.


Thank you so much! I hope to learn and make my own potion version from this :slight_smile:

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What was the reason for adding 470 here?

You can delete the node. It is from another project that didn’t use sine and it got copied over in a hurry.

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Ivan, this is great stuff, you made my life much easier! Is it possible to get the file you uploaded on Drive? The link is no longer working. Thanks for your help.


Hi Mark, I hope you will like it. Here is the new link.


The assets are made in Unreal 5.1, just put them in the content folder.
If it doesn’t automatically connect the reference, it is easy to set up, there is only one blueprint and two mesh with the provided two materials.