Convert Unity mask texture to occlusion / roughness / metal map

[Josh]

This extension adds a menu item in the texture editor that will do the necessary channel swizzle to convert a unity "mask texture" into the standard occlusion / roughness / metal map that Khronos glTF and Ultra use. After the process finishes you can save the texture, probably in DDS format with BC7 compression, and start using it. 

Unity Mask Texture.lua

[Josh]

If you want to convert a lot of files in a batch process, you can do something like this:

local dir = LoadDir("mask")

for n = 1, #dir do

    collectgarbage()

    local pixmap = LoadPixmap("mask/"..dir[n])
    if pixmap ~= nil then

        local x, y, r, g, b, a
        for x = 0, pixmap.size.x - 1 do
            for y = 0, pixmap.size.y - 1 do
                local rgba = pixmap:ReadPixel(x, y)
                r = Red(rgba)
                g = Green(rgba)
                b = Blue(rgba)
                a = Alpha(rgba)
                rgba = Rgba(g, 255 - a, r, 255)
                pixmap:WritePixel(x, y, rgba)
            end
        end

        pixmap:Save("mask/"..dir[n])    
    end
end