nc_extended_rotating/utility.lua

local minetest, vector, math_abs, math_sign
    = minetest, vector, math.abs, math.sign

local rotate_box_by_facedir = nc_extended_rotating.rotate.rotate_box_by_facedir

-- Default selection boxes for a node that doesn't have one them explicitly.
local DEFAULT_SELECTION_BOX = { min = vector.new(-0.5, -0.5, -0.5),
                                max = vector.new( 0.5,  0.5,  0.5) }

local utility = {}

-- Gets the active `selection_box` for the specified `node` which
-- has a `paramtype2` of `facedir`, based on its `param2` value.
function utility.get_node_active_selection_box(node)
    local def = minetest.registered_nodes[node.name]
    local box = def.selection_box and def.selection_box.fixed
    -- No need to rotate the default selection box.
    if not box then return DEFAULT_SELECTION_BOX end
    -- If node definition specifies multiple selection boxes, just pick the first (for now).
    if type(box[1]) == "table" then box = box[1] end
    -- Transform the `{ x1, y1, z1, x2, y2, z2 }` box to a `{ min, max }` one.
    box = { min = vector.new(box[1], box[2], box[3]),
            max = vector.new(box[4], box[5], box[6]) }
    -- Rotate the box to face `facedir`.
    rotate_box_by_facedir(box, node.param2)
    return box
end

-- Calculates the rotation vector from where a player is looking at on this node.
-- * If looking near an edge, the vector points in the direction of that edge.
-- * If looking near a corner, the vector similarly points in that direction.
-- * Otherwise, vector simply points away from the face.
function utility.rotation_vector_from_lookat(node, pointed_thing, edge_distance)
    local box    = utility.get_node_active_selection_box(node)
    local center = (box.min + box.max) / 2

    -- Calculate bounds, single vector describing the size of the selection box.
    local bounds = box.max - center -- This extends both into positive and negative.
    -- Calculate intersection point relative to these bounds.
    local point = pointed_thing.intersection_point - pointed_thing.under - center

    return point:combine(bounds, function(p, b)
        return b - math_abs(p) <= edge_distance and math_sign(p) or 0 end)
end

return utility