Mesh Reduction Discrepancy 5.4 vs 5.6

Development Pipeline & Plugins
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1

Hello,

we’ve just made the jump from 5.4 to 5.6 and have noticed that some of our simple meshes have many more triangles in their last LOD that they should have.

The mesh where we noticed only has 10 triangles in 5.4 but has 63 Triangles in 5.6 with the same settings.

In this particular mesh we have Reduction settings with termination Triangles at a Triangle Percentage of 2% but in 5.6 anything below 25% produces the same result.

Are these intentional changes or are we encountering a bug?

Regards Max

2

Steps to Reproduce
Load a very simple static mesh. Add an LOD. Use Reduction Settings with Termination Triangles and a very Low Percent Triangles to simplify the mesh.

Notice how the mesh does not get simplified as much as it was in 5.4.

3

Hello,

Thank you for reaching out.

I’ve been assigned this issue, and we will be looking into this change is reduction behavior for you.

4

Hello,

This is an intentional change. The minimum number of triangles a mesh will be reduced to was changed from 2 to 64 by CL: 37812770 on //UE5/Main.

The comment above the changed code reads:

// Keep a minimum of 64 triangles, to prevent already low-poly meshes from losing too much of their silhouette.Please let us know if this helps.

5

Hi,

seems like an odd choice to me to have this set in code directly like this as this seems like something that should be decided by the person creating the asset.

Regardless thank you for finding the change.

Regards,

Max

6

Hi Max,

The minimum triangle limit was changed to match Nanite’s behavior. Additionally, for some of our own projects, we noticed that something like a simple box mesh would get improperly reduced since we create a minimum of 3 LoDs per mesh by default. If you are ok with making a code change, you could revert this change to the previous limit of 2. We could make the minimum triangle limit a configurable option, but doing so will trigger a rebuild of the LoDs, which can be costly and needs to be evaluated to determine if it is worth doing. Let me know what you think.

7

Hello,

Thank you for the reply.

We are handing this to another team for further investigation and consideration.