If LVM or some other nonmetadata method is used to place a door,
then metadata is missing that tells us whether the door is left
or right-hinged.

However, we can detect that nodemeta is missing and see if the node
name is _a or _b. In the case of _a, nothing needs to be done and we
can just open the door. In the case of _b we assume the door is right
hinged, and tune the state nodemeta value so that the door opens the
right way. This all of course assumes that the schematic method places
the doors *closed* by default, which is reasonable.

We were cleverly attempting to use an airlike node as the
top half of the doors, but as airlike nodes are not walkable,
falling nodes would not stop falling and thus remain an entity
stuck on top of a door.

After inspecting the builtin/game/falling.lua code, I considered
the remaining options: (a) revert doors such that the top part is
actually the door, (b) play with nodedef fields and see if other
flags may work, or (c) modify the hidden door part to another
drawtype that properly prevents this issue.

(a) seemed way over the top for now, although it would solve the
issue, it would cause a rewrite of most of the code including the
old-door-conversion.

(b) turned up nothing.

(c) turned out to be relatively simple.

So, here's the implementation where I turn the hidden door top
into a tiny, non-targetable but walkable nodebox that is entirely
inside the door hinge. It's entirely transparent, so you still
can't see it, can't hit it, nor can you place anything in it or
make liquids flow through it. The top part is placed in the right
position on placement and not touched further.

Falling nodes will properly stop on top of these doors. I've
adjusted the door conversion code to properly account for the
issue as well, so the only thing remaining is people who have
been running a git branch - those can upgrade by re-placing the
door.

This was probably lost in either the API rewrite or a merge/rebase.

Fixes #929

I've found a favorable steel door sound from a parking garage
door that isn't abrupt or scary, just sounds like a nice solid
metal door. The sample had both opening and closing sounds, and
so they match nicely. Amplified and mixed several samples together
to reduce ambient noise, and get the right level compared to
wood doors. Attribution was added as well. CC-BY-3.0 sounds.

Fixes #909. Door tops are never flammable.

This doesn't guard yet against a voxelmanip removing the top node,
but that is less of an issue since if a voxelmanip removes the top,
then the bottom part remains functional and visibly intact. If the
voxelmanip removes the bottom part, but not the top, then this patch
makes it clean up the top just fine.

The access privilege allows players that have it to bypass protection
on locked doors/trapdoors, chests and bones.

The priv also allows bypassing any minetest.is_protected() check,
including digging nodes and placing them. It is meant for world
moderators to clean up and fix map issues.

Original patch by red-001. Split up and rebased/rewritten by sofar.

This patch requires https://github.com/minetest/minetest/pull/3800

This fence gate builds on NDT_CONNECTED by assuming fence nodes will
automatically connect to it's sides properly. The fence gate will
open and close just like doors, with sounds, but it only opens one
way. The gate sticks out quite a bit and can be bumped into, so the
fence may be used as some sort of path switch.

The fence gate offers no form of protection and can be opened and
closed by anyone. This is done on purpose - the fencegate isn't
meant to provide protection from players, as fences can be
trivially jumped over. Instead, these fences should be used for
protecting crops from hungry sheep, or keeping rabbits in their
pen, or just decoration. Mods can also modify the mod to add
protection, of course.

A recipe is added to make these. It's 4 sticks and 2 wood (any)
as follows:

  stick  wood  stick
  stick  wood  stick

The collision box of the open gate is such that if two gates are
connected but mirrored (making an M shape) then you can walk a large
entity that's larger than 1.0 wide through the opening. The gate of
an opened fence can also be stood upon or bumped into.

I've mixed together some sounds to provide a somewhat light sound
experience, one that one would expect from a small gate latching open
and close.

This change requires #873, otherwise it doesn't connect to fences.

https://forum.minetest.net/viewtopic.php?f=42&t=1523&start=500#p208773

Currently, doors can be placed inside others' protected areas. We
need to check protection for both bottom and top halves.

This is an adapted version of #861 - by oleastre

Most mods had been calling `doors.register_door() with a door
name that included the "modname:" prefix, and we should continue
to allow mods to do so, without registering the nodenames created
in the "doors:" namespace.

The default case is to use the "modname:" prefix verbatim. If
mods or code calls this function without a prefix, then "doors:"
is automatically used.

Now that the namespace is corrected, the copy replacement ABM is
no longer needed.

This function maps doors.register_door to the new API as far as
reasonable. We can't map the texture, so we fall back to a default
texture. An error message is printed if mod writers did not provide the
needed new tiles field for the door. The created doors are functional
and a full replacement. Old doors are replaced with the new ones
through an ABM.

A previous fix overwrote the `def` variable during registration,
causing protected doors no longer to be placed with protection.

Other mods may depend on knowing whether doors are placed
to setup additional attributes or perform node manipulations.

This is something e.g. mesecons does to connect circuits
to doors. This was tested with mesecons. Placing a door next
to a mesecon wire will make the wire automatically
connect, which was otherwise not happening.

And similarly, if we wield a door and right click any node
that has an on_rightclick() handler, call the handler
instead.

Just to be on the safe side, assure that none of this
code runs when right-clicking an entity or player, which
would likely crash the server.

Fold in PR #831 as well - prevent server crash on door
place on unknown blocks, by @tenplus1.

This code never allowed placing a door on e.g. a grass
plant. The code to handle this isn't that complex. With
this code, doors can be placed on flowers and on normal
node surfaces without issues.

This allows mod makers to register their own recipies, including
none, to register doors.

This patch replaces the default door nodes with a new mesh model
and nodes.

Two new models were added that are 2 blocks high. One for left-hinge
and one for right-hinge doors. This allows us to make a single texture
fit on both models. The alternative would have been 1 model and 2
unmapped textures, which is more work for mod developers.

Doors work exactly like the old doors, including ownership, breaking
doors, opening and closing.

Under the hood, we can prevent the top part of the door from being
obstructed by placing an invisible node. This prevents liquids from
flowing through doors or people placing sand or other blocks in the
top half. The door code automatically places and removes these as
needed.

Metadata is used to store door state, just like the old version.

A doors API is added, it allows mods to use the API to open/close or
toggle door states without worrying about sounds, permissions and
other details. This is intended for e.g. mesecons. This API allows
mods to manipulate or inspect doors for players or for themselves.

In-game old door nodes are automatically converted using an ABM and
preserve ownership and orientation and state.

TNT blows up all doors and trapdoors except for the steel ones,
who can survive a blast. We return an itemstack in on_blast(),
which requires a TNT API patch which is also pending.

We enable backface culling for most of these doors, as this gives
the identical visual appearance that the old doors had. In the case
of the glass door, there's a slight twist.

The texture files used by the new doors have new names that do
not conflict with previous texture file names to avoid texture
pack conflicts.

Thanks to red-001 <red-001@users.noreply.github.com> for some
of the conversion code, cleanups, and extra textures.

We're using a normal wooden side texture to draw the sides
of trapdoors. But the side textures have only 2 edges that
have a nice texture for the 2px wide trapdoor. We can
either repaint the textures, or just rotate the texture
properly for the two sides that need it.

Because the side texture for wooden doors was just a default:wood
texture, it clashes with the colors in the trapdoor, and so
we add a wooden trapdoor-matching tile side texture as well.

This also improves the steel trapdoor side, but without a
texture change there since that was already a specially
drawn texture for that node.

We also increase the thickness of the trapdoor to 2px. Right
now the model is 0.4 large, but this causes the side textures
to look odd as there's a mismatch in pixel size. By scaling the
trapdoor side up to exactly 2px, the sides look natural.

Thanks to @kilbith for the suggestion.

There really is no reason to prevent rotation in trapdoors, I
expect this to be an oversight.

Trapdoors work perfectly well sideways, upside down and can
work like fences, gates and more. Most commonly, people will
want to put them in the top half of the node so they remain
flush with a floor.

In oversight, I added this recipe not verifying that it was already
taken.

We change this to a 2x2 iron bar recipe. The shape and amount are
reasonable (reduced to output 1 steel trapdoor), and I verified that
it wasn't in use.

Fixes #779

Closes #770 - thanks to @tenplus1, @kilbith

Adds a steel trapdoor. Textures were painted from scratch, and
inspired by the current Steel Door. Ownership on the trapdoor
works as expected, and so does the crafting recipe.

Remove line if set to the default of 'true'

Implemented nodes:
- Steel Door: Ignores explosion
- Locked Chest: Ignores explosion
- Fire: Ignores explosion
- TNT: Starts burning
- Burning TNT: Explodes immediately
- Gunpowder: Starts burning
- Burning Gunpowder: Ignores explosion

can be registered by other mods

Screenshots at: https://github.com/minetest/minetest_game/issues/411

I think that was just a typo?

Mirror the setup of a door placed next to any door, not just next to
a door of the same type.  This is particularly useful where there are
multiple door types that have the same appearance, but one wants the
doors of a pair to have different behaviour in some other respect.