Mirrored objects have flipped binormal vectors in LookDev #62680

New Issue

yvt · 2019-03-17T15:11:54+01:00

yvt commented

2019-03-17 15:11:54 +01:00

System Information
Operating system: macOS 10.14.4 Beta (18E205e)
Graphics card: AMD Radeon R9 M295X 4GB

Blender Version
Broken:

2.79b
2.80 master (2d8aa2e6ad)

Short description of error

When rendering using the Material (2.79b) or LookDev (2.80) viewport shading mode, binormal vectors read by shaders are flipped for mirrored objects (i.e., objects having negative scale values for one or three axes).

Exact steps for others to reproduce the error
See the attached .blend file and screenshots.

Eevee Tangent Error Test (2.7).blend

The scene shows three shapes. The original shape is shown on the right side. The other ones are a mirrored version of the shape, each using a different method of mirroring: the middle one was produced by the Mirror modifier and the left one was created by copying the object and scaling by -1.0 on the X direction.

Their binormal vectors (presumably world-space) are visualized by mapping their XYZ coordinates to color values through the use of the Normal Map node.

The mirrored objects use the same transformation in regard to the original object. Therefore, it's expected that they have the same binormal vector. A Cycles render in Blender 2.79b shows an expected behavior:

However, when rendered using the Material (2.79b) or LookDev (2.80) viewport mode, the binormal vector of the left one (the one mirred by object scale) is flipped:

The following image shows a shading error possibly caused by this:

**System Information** Operating system: macOS 10.14.4 Beta (18E205e) Graphics card: `AMD Radeon R9 M295X 4GB` **Blender Version** Broken: - 2.79b - 2.80 `master` (2d8aa2e6ad351859796da8406a0c8f3cc2b45bbf) **Short description of error** When rendering using the Material (2.79b) or LookDev (2.80) viewport shading mode, binormal vectors read by shaders are flipped for mirrored objects (i.e., objects having negative scale values for one or three axes). **Exact steps for others to reproduce the error** See the attached `.blend` file and screenshots. [Eevee Tangent Error Test (2.7).blend](https://archive.blender.org/developer/F6839073/Eevee_Tangent_Error_Test__2.7_.blend) The scene shows three shapes. The original shape is shown on the right side. The other ones are a mirrored version of the shape, each using a different method of mirroring: the middle one was produced by the Mirror modifier and the left one was created by copying the object and scaling by `-1.0` on the X direction. Their binormal vectors (presumably world-space) are visualized by mapping their XYZ coordinates to color values through the use of the Normal Map node. The mirrored objects use the same transformation in regard to the original object. Therefore, it's expected that they have the same binormal vector. A Cycles render in Blender 2.79b shows an expected behavior: ![Screen Shot 2019-03-17 at 22.01.43.jpg](https://archive.blender.org/developer/F6839062/Screen_Shot_2019-03-17_at_22.01.43.jpg) However, when rendered using the Material (2.79b) or LookDev (2.80) viewport mode, the binormal vector of the left one (the one mirred by object scale) is flipped: ![Screen Shot 2019-03-17 at 22.48.27.jpg](https://archive.blender.org/developer/F6839065/Screen_Shot_2019-03-17_at_22.48.27.jpg) ![Screen Shot 2019-03-17 at 22.02.00.jpg](https://archive.blender.org/developer/F6839068/Screen_Shot_2019-03-17_at_22.02.00.jpg) The following image shows a shading error possibly caused by this: ![Screen Shot 2019-03-17 at 23.04.15.jpg](https://archive.blender.org/developer/F6839097/Screen_Shot_2019-03-17_at_23.04.15.jpg)

yvt commented

2019-03-17 15:11:54 +01:00

Added subscriber: @TomoakiKawada

Jacques Lucke commented

2019-03-18 13:02:47 +01:00

Added subscriber: @JacquesLucke

Jacques Lucke commented

2019-03-18 13:02:47 +01:00

Can you try to build this file again based on the default .blend file. This file links to some other .blend files.
Please try to keep it as simple as possible.

Can you try to build this file again based on the default .blend file. This file links to some other .blend files. Please try to keep it as simple as possible.

yvt commented

2019-03-18 14:56:19 +01:00

My apologies. Here's the new reproducing example created from scratch:

Eevee Tangent Error Test_3.blend

My apologies. Here's the new reproducing example created from scratch: [Eevee Tangent Error Test_3.blend](https://archive.blender.org/developer/F6844357/Eevee_Tangent_Error_Test_3.blend)

Sebastian Parborg commented

2019-03-18 15:40:09 +01:00

Added subscribers: @fclem, @ZedDB

Clément Foucault was assigned by Sebastian Parborg

2019-03-18 15:40:09 +01:00

Sebastian Parborg commented

2019-03-18 15:40:09 +01:00

@fclem I think there is already a ticket for this, but I can't find it ATM. So sorry if this is a duplicate.