GUI for custom shaders

[RomboDev]

Hi there,

we're looking to port rombotools (for Arnold) to Gaffer... https://www.rombo.tools/

They already work out-of-the-box but the UI is not what we're looking for for some materials.
Is there a way for example to change parameters names and params layout, group them etc ?

Appreciated some hints, thanks in advance.

[johnhaddon]

Yep, you can do that using an Arnold metadata (.mtd) file situated somewhere on the ARNOLD_PLUGIN_PATH. The best reference is probably the one we ship with Gaffer for the built-in Arnold shaders : https://github.com/GafferHQ/gaffer/blob/main/arnoldPlugins/gaffer.mtd.

Some specific examples from that file...

Specifying where a shader belongs within the NodeMenu :

gaffer.nodeMenu.category STRING "Rombo"

Putting a parameter in a collapsible group :

[attr specular]
		page STRING "Specular"

Changing the label for a parameter :

[attr scatter_secondary_anisotropy]
		label STRING "Secondary Anisotropy"

[RomboDev]

Oh great, was looking for that 'param in a collapsible group'. Looks like the group (beside attributes like .collapsed) is defined solely on the params decls and not like in Houdini/3dsMax .mtd where we have to first specify the group itself and its attributes . It's even smarter this way.. not sure however how to add 'separators' then as they are not params. Hopefully the .category will accept something like "Rombo/SSS" to create sub categories? Keeping open this discussion if eventually I'll have something to ask further.

Thanks for the hints !

[johnhaddon]

Hopefully the .category will accept something like "Rombo/SSS" to create sub categories?

Yep, that works. You can also do subsections with page STRING "SectionName.SubSectionName".

not sure however how to add 'separators' then as they are not params

You can add a horizontal dividing line underneath a specific attribute like so :

[attr diffuse_roughness]
		gaffer.layout.divider BOOL true

[RomboDev]

It's taking a bit of work because we have almost 40 shader nodes and around 500 params to address but it all seems getting out pretty well.. loving Gaffer ! One last thing hopefully.. how about parameter ranges.. it doesn't seem Gaffer obeys metadata from the compiled shader params as almost all the DCCs ... ie.

AiParameterFlt("sssMieScatter", 0.f);
AiMetaDataSetFlt(nentry, "sssMieScatter", "min", 0.f);
AiMetaDataSetFlt(nentry, "sssMieScatter", "softmax", 10.f);
AiMetaDataSetFlt(nentry, "sssMieScatter", "max", 100.f);

am I missing something or is there maybe param attributes like min/max (and softmin/softmax) to add to the .mtd ?

[johnhaddon]

It looks like we don't support the min or max metadata yet, but we definitely should - would you mind opening an issue for it at https://github.com/GafferHQ/gaffer/issues? Bear in mind that this will limit the values that the user can enter, but won't create a slider widget - see #5415 for some discussion around that.

[RomboDev]

Done ! I mean adding the issue you suggested.