nether/portal_api.txt

Portal API Reference
====================

The portal system used to get to the Nether can be used to create portals
to other realms.

Pick a node type to have your portals built from, a shape in which the
portals must be built, and provide 3 functions for portals to find their
destination with:
 * `find_realm_anchorPos(surface_anchorPos)`
 * `find_surface_anchorPos(realm_anchorPos)`
 * `is_within_realm(pos)`

Optionally decorate by choosing portal colors, particles, media etc.

See `init.lua` and `portal_examples.lua` for examples of 3 different portals.

Portal code is more efficient when each type of portal uses a different type
of node to build its frame out of - consider creating your own node for
players to build portals from. However it is possible to register more than
one kind of portal with the same frame material — such as obsidian — provided
the size of the PortalShape is distinct from any other type of portal that is
using the same node for its frame, and portal sizes remain small.

Stone is not a good choice for portal frame nodes as the Minetest engine may
convert it into terrain nodes if the biome-pass occurs after the portal is
created. Similarly, avoid using nodes which may be replaced by ABMs or
docoration functions without triggering the node's `on_destruct` handler.


Realms
------

This API uses the concept of a "realm" for each type of portal. If a portal is
outside its realm then it links to a portal inside the realm, if a portal is
inside its realm then it links to the outside.

You get to decide what consitutes your realm by implementing the function
`is_within_realm(position)`.

For example, the Nether realm is defined as existing at a certain depth and
anything above that depth is considered outside the Realm.

In contrast, the "Surface portal" - an example in portal_examples.lua, only
uses one realm. Its `is_within_realm()` function always returns true so that
any time a portal is opened it will use `find_surface_anchorPos()`.

Note that the name "find_surface_anchorPos" is a Nether-centric misnomer, as
different types of portals are free to use different definitions of a realm
such that leaving the realm might not be synonymous with travelling to the
surface.


Helper functions
----------------

* `nether.volume_is_natural(minp, maxp)`: returns a boolean
    * use this when determining where to spawn a portal, to avoid overwriting
      player builds. It checks the area for any nodes that aren't ground or
      trees.
      Water will fail this test, unless it is unemerged.

* `nether.find_surface_target_y(target_x, target_z, portal_name)`: returns a
  suitable anchorPos
    * Can be used when implementing custom find_surface_anchorPos() functions
    * portal_name is optional, providing it allows existing portals on the
      surface to be reused.

* `nether.find_nearest_working_portal(portal_name, anchorPos, distance_limit, y_factor)`: returns
  (anchorPos, orientation), or nil if no portal was found within the
  distance_limit.
    * A y_factor of 0 means y does not affect the distance_limit, a y_factor
      of 1 means y is included (the default if y_factor is nil), and a y_factor
      of 2 would squash the search-sphere by a factor of 2 on the y-axis, etc.
    * Only portals in the same realm as the anchorPos will be returned, even if
      y_factor is 0.
    * Pass a nil (or negative) distance_limit to indicate no distance limit


API functions
-------------

Call these functions only at load time:

* `nether.register_portal(name, portal_definition)`
    * Returns true on success. Can return false if the portal definition
      clashes with a portal already registered by another mod, e.g. if the size
      and frame node is not unique.
      A false return value should be handled, you could:
        * Fall back to using a secondary material for portals to be built with.
        * Use error() to exit lua with a message explaining how two mods are
          clashing and how it can be resolved.
        * Continue without a portal (the reason will be logged for the user).
* `nether.unregister_portal(name)`
    * Unregisters the portal from the engine, and deletes the entry with key
      `name` from `nether.registered_portals` and associated internal tables.
    * Returns true on success
    * You will probably never need to call this, it exists only for completeness.
* `nether.register_portal_ignition_item(name, ignition_failure_sound)`
    * ignition_failure_sound is optional, it plays any time an attempt to use
      the item occurs if a portal is not ignited.
* `nether.register_wormhole_node(name, nodedef_overrides)`
    * Can be used to register wormhole nodes with a different post_effect_color
      from the "nether:portal" node. "Post effect color" is the tint the world
      takes on when you are standing inside a portal. `post_effect_color` is the
      only key/value that is needed in the nodedef_overrides table to achieve that,
      but the function allows any nodedef key/value to be specified/overridden.
    * After `register_wormhole_node()`, invoke `register_portal()` and include
      `wormhole_node_name` in the portal_definition, assigning it the name of the
      new wormhole node.


Portal definition
-----------------

Used by `nether.register_portal`.

    {
        frame_node_name     = "default:obsidian",
        -- Required. For best results, have your portal constructed of a
        -- material nobody else is using.

        shape = nether.PortalShape_Traditional,
        -- Optional.
        -- Shapes available are:
        --     nether.PortalShape_Traditional (default)
        --     nether.PortalShape_Circular
        --     nether.PortalShape_Platform
        -- New shapes can be created, but are beyond the scope of this guide.

        wormhole_node_name  = "nether:portal",
        -- Optional. Allows a custom wormhole node to be specified.
        -- Useful if you want the portals to have a different post_effect_color
        -- or texture.

        wormhole_node_color = 0,
        -- Optional. Defaults to 0/magenta.
        -- A value from 0 to 7 corresponding to the color of pixels in
        -- nether_portals_palette.png:
        --     0 traditional/magenta
        --     1 black
        --     2 blue
        --     3 green
        --     4 cyan
        --     5 red
        --     6 yellow
        --     7 white

        particle_color      = "#808",
        -- Optional. Will default to a colour matching the wormhole_node_color
        -- if not specified.

        particle_texture    = "image.png",
        -- Optional. Hardware colouring (i.e. particle_color) is applied to
        -- this texture, use particle_texture_colored instead if you want to
        -- use the colors of the image.
        -- Animation and particle scale may also be specified, e.g:
        -- particle_texture = {
        --      name = "nether_particle_anim1.png",
        --      animation = {
        --          type = "vertical_frames",
        --          aspect_w = 7,
        --          aspect_h = 7,
        --          length = 1,
        --      },
        --      scale = 1.5
        --  },
        -- See lua_api.txt for Tile Animation definition
        -- Some animated and non-animated textures are provided by this mod:
        --     nether_particle.png          (original)
        --     nether_particle_anim1.png    (stars)
        --     nether_particle_anim2.png    (bubbles)
        --     nether_particle_anim3.png    (sparks)
        --     nether_particle_anim4.png    (particles)

        title = "Gateway to Moria",
        -- Optional. Provides a title for the portal.
        -- Used in the Book of Portals or Help modpack.

        book_of_portals_pagetext = "Everything I need the player to know",
        -- Optional. Provides the text for the portal in the Book of Portals
        -- and Help modpack.
        -- The Book of Portals is a book that can be found in chests, and
        -- provides players with instructions on how to build and use the
        -- portal, so be sure to mention the node type the frame must be built
        -- from.
        -- This can also provide flavortext or details about where the portal
        -- will take the player.

        sounds = {
            ambient    = <SimpleSoundSpec>,
            -- if the ambient SimpleSoundSpec is a table it can also contain a
            -- "length" int, which is the number of seconds to wait before
            -- repeating the ambient sound. Default is 3.
            ignite     = <SimpleSoundSpec>,
            extinguish = <SimpleSoundSpec>,
            teleport   = <SimpleSoundSpec>,
        }
        -- sounds is optional

        within_realm = function(pos),
        -- Required. Return true if a portal at pos is in the realm, rather
           than the surface world.

        find_realm_anchorPos = function(surface_anchorPos),
        -- Required. Return a position in the realm that a portal created at
        -- surface_anchorPos will link to.
        -- Return an anchorPos or (anchorPos, orientation)
        -- If orientation is not specified then the orientation of the surface
        -- portal will be used.
        -- If the location of an existing portal is returned then include the
        -- orientation, otherwise the existing portal could be overwritten by
        -- a new one with the orientation of the surface portal.

        find_surface_anchorPos = function(realm_anchorPos),
        -- Optional. If you don't implement this then a position near the
        -- surface will be picked.
        -- Return an anchorPos or (anchorPos, orientation)
        -- The name of this function is a Nether-centric misnomer. It should
        -- return a position outside the realm, and different types of portals
        -- are free to use different definitions of a realm such that leaving
        -- the realm might not be synonymous with travelling to the surface.
        -- If orientation is not specified then the orientation of the realm
        -- portal will be used.
        -- If the location of an existing portal is returned then include the
        -- orientation, otherwise the existing portal could be overwritten by
        -- a new one with the orientation of the realm portal.

        on_run_wormhole      = function(portalDef, anochorPos, orientation),
        -- invoked once per second per portal
        on_extinguish        = function(portalDef, anochorPos, orientation),
        -- invoked when a portal is extinguished, including when the portal
        -- it connected to was extinguished.
        on_player_teleported = function(portalDef, player, oldPos, newPos),
        -- invoked immediately after a player is teleported
        on_ignite            = function(portalDef, anochorPos, orientation)
        -- invoked when a player or mesecon ignites a portal
        on_created           = function(portalDef, anochorPos, orientation)
        -- invoked when a portal creates a remote twin, this is usually when
        -- a player travels through a portal for the first time.
    }