Optional per-part masks

[RichardDastardly]

I can see a few levels of masking possible - don't allow too much feature creep. Masking should disable the blending controls given the return UV value is the blending value.

Feature:

• Simple UV mask, insert 0-1 value into blending calc
• Two-colour blend with UV mask - use red & green channels for blending values for two colours, and UV mask as above. Three colours should be possible if there's some very strict rules about blending, or the shader output is going to be hell.
• Mask should be an optional entry in the partconfig & of some default type, don't deal with loading it ourselves.

Notes:

• Check how shaders manage the non-appearance of a map ( the PBR shader will probably handle this ).
• Consider how to handle saturation carefully - may want to leave the blend saturation threshold active although that will cost a conversion to HSV.
• This is almost a different mod - consider some separation & abstraction.

Affects:

• Part load/save
• Menu
• Shader

[RichardDastardly]

This has changed somewhat, given I have a new shader which can have up to 255 colour areas. Using blending to mask off precoloured areas is on the cards still, so this is not a completely different mod.

[RichardDastardly]

This is now a feature. Stick "Map = BlendMask, path/to/blendmask" in the part cfg/patch & it'll get picked up automatically.

The mask should be a loadable greyscale texture ( so actually RGB of some sort ) with no alpha.

[RichardDastardly]

Additionally per part bump + emissive maps should work, even for parts which didn't have them originally. Map = Emissive,path Map = BumpMap,path