UE4 applies 1-x transform to V coordinate when importing UVs from mesh. This is to handle GL/D3D differences in texture origin, but it breaks UDIM page addressing. It's possible to apply a fix to imported UVs, but this will break UVs intended for wrapped sampling, rather than UDIM sampling. Alternately, UE4 could adjust UDIM layout to match the modified UVs.
Import texture/mesh from the attached udimTest.zip. UDIM tiles should show up on the grid mesh with 1001 in the lower left corner, with X-axis increasing to the right, and Y-axis increasing upwards.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-89138 in the post.
| 0 |
| Component | UE - Graphics Features |
|---|---|
| Affects Versions | 4.25 |
| Target Fix | 4.26 |
| Created | Feb 19, 2020 |
|---|---|
| Resolved | Mar 23, 2020 |
| Updated | Sep 19, 2021 |