Lambert shading error in blender internal #43789

New Issue

Fabian Emmes · 2015-02-23T16:14:40+01:00

Fabian Emmes commented

2015-02-23 16:14:40 +01:00

System Information
Windows 8.1, i5, Sandy Bridge

Blender Version
Broken: 2.73a

Short description of error
Lambert shading of face is wrong, changing different part of mesh corrects shading.

Exact steps for others to reproduce the error
Open render_internal_diffuse.blend.
Press F12 to render.
Notice that both large faces are rendered differently.

Setup of scene and explanation why I think this is a bug
The sun is perfect white, and shines with 45 degree on the white object.
The material has no specular intensity and its diffuse color/intensity is perfect white.
By the Lambert model, the model should be shaded with cos(45 deg) = 0.707.
Only one of the faces is shaded with this intensity, the other is too dark (0.6224)

After removing one or both of the small faces right of the large faces, both large faces render with the correct intensity.

**System Information** Windows 8.1, i5, Sandy Bridge **Blender Version** Broken: 2.73a **Short description of error** Lambert shading of face is wrong, changing different part of mesh corrects shading. **Exact steps for others to reproduce the error** Open [render_internal_diffuse.blend](https://archive.blender.org/developer/F145439/render_internal_diffuse.blend). Press F12 to render. Notice that both large faces are rendered differently. **Setup of scene and explanation why I think this is a bug** The sun is perfect white, and shines with 45 degree on the white object. The material has no specular intensity and its diffuse color/intensity is perfect white. By the Lambert model, the model should be shaded with cos(45 deg) = 0.707. Only one of the faces is shaded with this intensity, the other is too dark (0.6224) After removing one or both of the **small** faces right of the large faces, both large faces render with the correct intensity.

Fabian Emmes commented

2015-02-23 16:14:40 +01:00

Changed status to: 'Open'

Fabian Emmes commented

2015-02-23 16:14:40 +01:00

Added subscriber: @der_fab

Sergey Sharybin self-assigned this 2015-02-24 08:48:15 +01:00

Sergey Sharybin commented

2015-02-24 08:48:15 +01:00

Will have a look later.

Campbell Barton commented

2015-03-11 08:55:53 +01:00

Added subscriber: @ideasman42

Campbell Barton commented

2015-03-11 08:55:53 +01:00

Firstly, one of the faces has smooth set, and the other not, this is making the ray-bias treat the faces differently.

It seems to be working as intended, (but agree the final result is odd).

Auto-bias will use ob->smoothresh set by set_phong_threshold
This is set based on the difference in normals (which is why the small faces at the right make a difference).
Then shade_one_light is using smoothresh when MA_RAYBIAS is set.

Firstly, one of the faces has smooth set, and the other not, this is making the ray-bias treat the faces differently. It seems to be working as intended, (but agree the final result is odd). - Auto-bias will use `ob->smoothresh` set by `set_phong_threshold` - This is set based on the difference in normals (which is why the small faces at the right make a difference). - Then `shade_one_light` is using `smoothresh` when `MA_RAYBIAS` is set.

Fabian Emmes commented

2015-03-11 09:40:41 +01:00

I don't understand how faces, that are not connected to the problematic part, can have influence on its shading. Is this behavior documented somewhere?

We are using blender (internal) for lightmap baking and are getting different shadings on large areas due to this problem. Can this problem be fixed or should we work around it somehow? Is there an easy way to identify faces with different shading modes in the 3D View?

Thanks a lot!

I don't understand how faces, that are not connected to the problematic part, can have influence on its shading. Is this behavior documented somewhere? We are using blender (internal) for lightmap baking and are getting different shadings on large areas due to this problem. Can this problem be fixed or should we work around it somehow? Is there an easy way to identify faces with different shading modes in the 3D View? Thanks a lot!

Sergey Sharybin commented

2015-03-17 18:40:16 +01:00

Changed status from 'Open' to: 'Archived'

Sergey Sharybin closed this issue

2015-03-17 18:40:16 +01:00

Sergey Sharybin commented

2015-03-17 18:40:16 +01:00

Well, @ideasman42 is more or less explained everything already.

Seems there's a bit of confusion here tho -- one of big faces is set to smooth shading. It makes it shaded differently comparing to the one adjacent to it. Setting shading to flat to both big connected faces makes them shaded the same way.

I don't think it's a problem, just how shading works. Workaround and fix would be to set proper smoother flag.

Don't think there's existing way to show smooth faces, but it's easy to do with a python script.

Thanks for the report, but wouldn't consider it a bug.

Well, @ideasman42 is more or less explained everything already. Seems there's a bit of confusion here tho -- one of big faces is set to smooth shading. It makes it shaded differently comparing to the one adjacent to it. Setting shading to flat to both big connected faces makes them shaded the same way. I don't think it's a problem, just how shading works. Workaround and fix would be to set proper smoother flag. Don't think there's existing way to show smooth faces, but it's easy to do with a python script. Thanks for the report, but wouldn't consider it a bug.

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Lambert shading error in blender internal #43789