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Is DEBUG_METALLIC_ROUGHNESS used? #600

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andrewvarga opened this issue Feb 3, 2025 · 4 comments · May be fixed by KhronosGroup/glTF-Sample-Renderer#20
Open

Is DEBUG_METALLIC_ROUGHNESS used? #600

andrewvarga opened this issue Feb 3, 2025 · 4 comments · May be fixed by KhronosGroup/glTF-Sample-Renderer#20
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@andrewvarga
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This option is listed in debugOutputMapping, but mr.METALLIC_ROUGHNESS is actually undefined.
There is also some code in pbr.frag referring to it but it doesn't do much:

    // If the MR debug output is selected, we have to enforce evaluation of the non-iridescence BRDF functions.
#if DEBUG == DEBUG_METALLIC_ROUGHNESS
#undef MATERIAL_IRIDESCENCE
#endif

Maybe it used to be there and got partially removed?
The option is not available to select on the UI (only metallic and roughness separately).
I would think either the option should be added to the UI + the shader code (if it's useful to visualize both metallic and roughness at the same time), or probably simpler to just remove it from everywhere.
@UX3D-haertl
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Seems like we missed this after the shader refactoring last year which made this debug channel obsolete.
Thanks for pointing that out. I will remove the unused code.

@andrewvarga
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Seems like we missed this after the shader refactoring last year which made this debug channel obsolete. Thanks for pointing that out. I will remove the unused code.

Great. Is it obsolete because now there is a separate metallic and roughness option?

@UX3D-haertl
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There were only specular and diffuse values in the old simplified shader code. And the contributions of the different PBR features/extensions were added. Therefore, the contribution of metallic roughness could be shown easily.

Now we strictly follow the BRDF diagrams from the spec (and the modifications extensions apply to this diagram)

Image

Therefore, it does not really make sense to have a debug channel for the metallic roughness contribution, since it is also effected by other extensions.
With the new approach one can debug the different factors of the equations.
You can disable extensions, if you want to only see the metallic effect, but this could be misleading, since extensions do modify the formula.

@UX3D-haertl
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E.g. the transmission extensions modifies the above diagram:

Image

@UX3D-haertl UX3D-haertl linked a pull request Feb 4, 2025 that will close this issue
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Remove unused debug channel code KhronosGroup/glTF-Sample-Renderer
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@andrewvarga @UX3D-haertl