art.prop_glow

Surface shader for Smog's generated props. Samples the prop's own albedo, normal and packed roughness/metal maps (glTF packing: G roughness, B metal) on mesh UVs, then:

• metal_scale damps the generator's habit of painting everything as metal;
• coat lays a rain film over it;
• glow_* lights only bright texels (glow_lum_lo..glow_lum_hi luminance) between world heights glow_min_y and glow_max_y, with a per-position flicker: a gas lamp's glass panes glow, its iron frame does not.

Used by the art/props/*.material set the district and gasworks spawn.