luadiant POC - clip all terrain to breadth of 2 units

luadiant-poc-auto-clip-terrain.lua

-- clip all terrain to breadth of 2 units
local hits = {}

-- find all terrain brushes
for _,b in ipairs(rad.allBrushes()) do
    local terrain_face = nil
    for _,f in ipairs(b:getFaces()) do
        local texture = f:getTexture()
        if texture == "textures/common/caulk" then
        else
            -- we skip brushes with more than 1 non-caulk face
            if terrain_face ~= nil then
                goto skip_brush
            end

            -- we skip brushes with any non-terrain face
            if not string.find(texture, ".*terrain.*") then
                goto skip_brush
            end

            terrain_face = f
        end
    end

    -- we skip brushes with no terrain-face at all
    if terrain_face == nil then
        goto skip_brush
    end

    table.insert(hits, {b, terrain_face})

    ::skip_brush::
end

rad.deselectAll()

-- clip em all
for _,hit in ipairs(hits) do
    local brush = hit[1]
    local face  = hit[2]

    -- determine normal vector and scale by 2 and invert
    local nv3d = face:getNormalVector()
    do
        local nv3dv = nv3d:getValues()
        local x = nv3dv[1] * 2 *-1
        local y = nv3dv[2] * 2 *-1
        local z = nv3dv[3] * 2 *-1
        nv3d:setValues({x, y, z})
    end

    -- get terrain plane and translate by previous normal vector
    local terrain_plane = face:getPlanePoints()
    terrain_plane[1]:add(nv3d)
    terrain_plane[2]:add(nv3d)
    terrain_plane[3]:add(nv3d)

    -- clip the brush (@TODO without selecting/deselecting and UndoableCommand which makes things really slow)
    brush:select()
    rad.clip(ClipperPoints(terrain_plane[3], terrain_plane[2], terrain_plane[1], 3), false)
    brush:deselect()
end