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Mirrored UV have bad tangent space
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Mirrored UVs produce bad normal map output. This is due to tangent calculation/upload to GPU.

Even more strange is the fact that building without cycles gives a different result.

2.8 With Cycles (only left half is correct (switch to cycles to see correct result)

2.8 Without Cycles (seems completly inverted)

This was with debug build by the way.

Event Timeline

Clément Foucault (fclem) lowered the priority of this task from Needs Triage by Developer to Confirmed, Medium.Jan 10 2018, 10:10 AM
Clément Foucault (fclem) created this task.

The mirrored UV's are a copy in this case - not a continuous unwrap, so there are seams.

The difference without cycles is it's using Blender-Internal rendering engine. Which uses flipped tangents.
(double checked and this is the case for 2.79).

So there is no bug here as far as I can see.

My bad the description is not good.

I should have stated that the screenshot "2.8 with cycles" is faulty. If you compare it to the cycles rendered results.

The problem is not the seam but the tangent direction.

This is the expected result.

I have similar problem and I posted this problem on Blenderartists.

In short: every mirrored UV island with baked normal maps doesn't work in Eevee.

Consider having this ready for the beta milestone

this is how the mirrored uvs show in eevee

this is how they look in cycles

just wanted to know if there's a way to fix it in eevee