Summary
In UE 5.8, overlapping planar meshes using a Masked material produce z-fighting artifacts in areas that should be fully discarded by the opacity mask. The same setup worked previously in UE 5.5.
What Type of Bug are you experiencing?
Rendering (Graphics / Niagara)
Steps to Reproduce
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Create two plane meshes.
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Place them close together (e.g. overlapping) and uzing the same depth (z value).
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Create a simple Masked + Unlit material, with the RGB values of a transparent texture plugged into the emissive colour value, and its alpha value plugged into the opacity mask value.
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Apply the masked + unit material to both meshes.
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Look at the intersecting areas of both meshes and the z-fighting artefacts that appear between the transparent areas of one mesh, and the opaque areas of another mesh.
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Move the camera around and see how the z-fighting artefacts only occur on these areas.
Expected Result
Fully masked-out pixels should not contribute depth or interfere with other overlapping masked surfaces.
Observed Result
Horizontal/diagonal striped artifacts appear and move with the camera, consistent with z-fighting/depth-buffer competition. The interference occurs in pixels that should have been discarded by the opacity mask.
Affects Versions
5.8
Platform(s)
Windows
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For crash reports, include your callstack
No crashes.
Additional Notes
- Works correctly in UE 5.5.
- Reproduces in UE 5.8.
- Switching the same material to Translucent removes the issue.
- Reproduces with a minimal Masked/Unlit material.
- r.EarlyZPassOnlyMaterialMasking 1 does not change the behavior.
- Nanite not enabled on the planes.
- Virtual textures not being used, etc…