alpha mode in styling json

[bertt]

In release 2.15 there is an option to set the alpha mode: --default_alpha_mode (OPAQUE/BLEND/MASK)

For a more granular approach we can add support for alpha mode in the styling json. This way we can use alpha blending in a subset of geometries or in parts of geometries

[bertt]

Proposal for alpha mode in style.json:

Default: OPAQUE Options: OPAQUE, MASK, BLEND

{
    added-->> "AlphaModes":[list_of_alpha_modes],  --<<added
    "EmissiveColors": [list_of_emissivecolors in hex],
    "PbrMetallicRoughness": {
        "BaseColors": [ list_of_basecolors in hex],
        "MetallicRoughness": [list_of_metallic_roughness in hex]
    },
    "PbrSpecularGlossiness": {
        "DiffuseColors": [list_of_diffuse in hex],
        "SpecularGlossiness": [list_of_specular_glossiness in hex]
    }
}