raze-gles/polymer/eduke32/source/lunatic/doc/lunatic.txt

Lunatic User Manual
===================
Helixhorned <contact: Duke4.net forums>
:max-width: 56em
:numbered:
:icons:



Introduction
------------


Language
--------
:Lua51: http://www.lua.org/about.html
:Lua51Ref: http://www.lua.org/manual/5.1/
:PiL: http://www.lua.org/docs.html

:LuaJIT: http://luajit.org
:LuaJIText: http://luajit.org/extensions.html

The base language for writing Lunatic user code is {Lua51}[Lua 5.1].  It is
extensively documented in a {Lua51Ref}[Reference Manual], as well as described
more broadly and accessibly in the {PiL}[Programming in Lua] books.
// TODO: describe Lua a bit
// TODO: give hints which PiL to read / how

Because Lunatic is implemented using {LuaJIT}[LuaJIT], a just-in-time compiler
for the Lua language, some {LuaJIText}[extensions] to the core language are
automatically available. They may be used if no compatibility with Rio Lua 5.1
is desired.footnote:[Not all extensions from LuaJIT are available, since some
like the FFI are targeted at C programmers rather than scripting coders.]

NOTE: The length operator (`#`) for table arguments should be taken to be
defined by the http://www.lua.org/manual/5.2/manual.html#3.4.6[stricter wording
of Lua 5.2].


Environment and Usage
---------------------

Lunatic aims to provide a _safe_ scripting environment for EDuke32. Thus, not
all of Lua's functionality is available in Lunatic, and some is slightly
altered to play well with being embedded into a game, or to prevent commonly
occurring mistakes.

.Differences from default Lua environment
- Creating new global variables in the global environment is forbidden.
- In module context, referencing a non-existent variable (i.e. one that has
  value *nil*) is an error.

EDuke32 can load multiple Lunatic _modules_ when starting up. This is always
done after translating CON code to Lua and loading it. Such modules must be
named `*.lua` (case-sensitive) and should be passed directly, without any
option letters, at the command line. Directory separators must be forward
slashes.

.Invocation example
====================
`eduke32 -nologo MYTC.CON -mx addition.con test.lua weapons/nuke.lua -v1 -l1`
====================


Global Environment
------------------

When a Lua module is loaded, its global environment contains both selected
functions from core Lua, as well as Lunatic's own pre-defined variables.
These allow access and manipulation of EDuke32 engine and game data.

[icon="icons/din_w_explosive.png"]
CAUTION: If an attempt is made to create a new variable in the global
environment or to assign any value to an existing variable, the behavior is
undefined.

Lua functions
~~~~~~~~~~~~~

The following base Lua functions are available in Lunatic's global environment:

`assert`, *`error`*, `ipairs`, `pairs`, `pcall`, *`print`*, *`module`*, `next`,
*`require`*, `select`, `tostring`, `tonumber`, `type`, `unpack`, `xpcall`.

The bold ones add functionality or behave slightly differently, described below.
Additionally, `printf` is provided for convenience.

[[error]] *`error(message [, level])`*::
In Lunatic, errors also print to the on-screen display (OSD) and are written to
the log (unless a maximum error count is exceeded). These also have a
_backtrace_ added. Additionally, errors not caught by a `pcall` result a
permanent message to appear on the screen, containing the source file name and
line number.

*`print(...)`*::
The messages are printed to the OSD and the log. Color codes available in
EDuke32 (e.g. `^10` for dark red) are interpreted. Overriding `tostring` has no
effect on Lunatic's `print` as it uses the initial, built-in `tostring`
function instead of looking it up in the global environment.

*`printf(fmt, ...)`*::
Calls `print` with the result of `string.format(fmt, ...)`.

Writing and using modules
~~~~~~~~~~~~~~~~~~~~~~~~~

In Lunatic, like in Lua, a _module_ is a conceptually a sort of package that
unites related bits of functionality. Language-wise, it is simply a Lua
table holding its contents, as described and motivated at length in
_Programming in Lua_.

The ``creation'' and ``usage'' sides of the modularity concept are reflected in
two functions known from Lua 5.1, `module` and `require`. The former is a
convenient way of separating the _import_, potential _gamevar_, and main body
sections when writing a package. It is not required to use `module`, but it is
the only way to declare _game variables_, that is, variables that EDuke32
stores within savegames, recreating their values when they are loaded.

The other side of the coin, `require`, is also used like in Lua: ``including''
a named module is requested by passing its name to `require`. This searches for
a matching module, loading and running it if the request happens for the first
time.

==== The function `require(modname, ...)`

Attempts to find a Lua or Lunatic module named `modname`. The name can refer to
a _built-in_ module, of which the following ones are allowed:

* The http://bitop.luajit.org/[`bit`] module for bitwise operations
* `math`, `string` and `table`, base modules from Lua
* Lua's `os` module, containing a single function, `clock`. Like the
  <<timing_funcs,timing functions>>, it should only be used to profile bits of
  code.
* Modules provided by Lunatic, which are described in <<ext_api,their own
  section>>.

If `modname` does not designate a built-in module, Lunatic first replaces every
dot contained in it with a directory separator. Then, it looks for a file with
that base name suffixed with `.lua` in the EDuke32 search path (virtual file
system, GRP, ZIP). Using directory separators directly is not allowed.

The loaded module is protected so that write accesses to its table yield
errors. Unlike in Lua, our `require` does not return *true* when a module is
requested that has not yet finished loading (that is, the inclusion chain
contains a loop). Instead, an error is raised.

Lunatic's `require` allows passing additional arguments to the module to load.
On the module side, they can be obtained by examining the vararg expression
``++\...++'' at file scope. Given a definition of `args` as `{...}`, its first
element `args[1]` would contain `modname` and the following entries the values
passed in addition to `require`. This feature is useful for parametrizing a
module: for example, the module could provide a way alter the starting tile
number of an actor it defines.

Issuing `require` for some special names listed below has a predefined meaning
that cannot be overridden by the user.

* `CON.DEFS`: returns a table mapping labels ++define++d from CON to their
values, except for `NO`.

* `CON.ACTION`: returns a table mapping labels of ++action++s defined from CON
  to immutable <<con_action,`con.action`>> objects.

* `CON.MOVE`: returns a table mapping labels of ++move++s defined from CON
  to immutable <<con_move,`con.move`>> objects.

* `CON.AI`: returns a table mapping labels of ++ai++s defined from CON
  to immutable <<con_ai,`con.ai`>> objects.

* `end_gamevars`: used to mark the end of a gamevar block, described below.


==== The `module()` function

Initiates a _module_ environment by creating a new empty table and setting it
as the global environment of the chunk.  Unlike Lua 5.1, our `module` takes
neither a name argument nor ``option'' varargs. A Lunatic file may have at most
one call to `module`, which (if there is one) *must* be called at file scope.

===== Game variables

Lunatic has a special mechanism to mark variables that represent persistent
state and whose values should be stored in savegames. If such variables are
desired, they must be initialized between the `module` call in a Lua file and a
closing `require("end_gamevars")`.footnote:[The reason that the initialization
has to happen between the `module` and the `require('end_gamevars')` is that on
savegame loading, gamevars are restored from the latter.] These variables may
also be *`local`*.

Game variables may take on only values of types that Lunatic knows how to
serialize into savegames. These are the following:

* Booleans, numbers, and strings, collectively called the _basic types_
* Custom Lunatic types that are labeled _serializeable_ in their documentation
* Tables, but with the following restrictions on their contents:
** A table key may only be of basic type.
** A table value may be (a reference to) any serializeable object, but tables
    or Lunatic objects that are so referenced *must* have originated in the
    gamevar section of the same module. Beyond that, there are no restrictions
    on the table topology.

[icon="icons/din_w_collapse.png"]
CAUTION: If a gamevar contains a value that is not serializeable at any point
in the execution, the behavior is undefined. Note that in particular, gamevars
are not allowed to take on the value *nil*.

// TODO: example?

// TODO: the rest


The ``gv'' variable
~~~~~~~~~~~~~~~~~~~

Some constants, global C variables, and miscellaneous functions and structures
are accessible via the global `gv` variable.

Constants
^^^^^^^^^
`gv.MAXSECTORS`, `gv.MAXWALLS`, `gv.MAXSPRITES`::
The hard engine limits on the number of sectors, walls, and sprites. These
constants *must* be used instead of any literal numeric values because they
can change depending on how EDuke32 was configured and built.

//////////
`gv.MAXSTATUS`, `gv.MAXTILES`, `gv.MAXSPRITESONSCREEN`::
TODO

`gv.MAXBUNCHES`, `gv.CEILING`, `gv.FLOOR`::
TODO
//////////

`gv.CLIPMASK0`::
A clipping (collision detection) mask specifying to consider only _blocking_
walls and sprites.

`gv.CLIPMASK1`::
A clipping (collision detection) mask specifying to consider only _hitscan
sensitive_ walls and sprites.

// Game-side
`gv.*` inventory indices::
`GET_STEROIDS`, `GET_SHIELD`, `GET_SCUBA`, `GET_HOLODUKE`, `GET_JETPACK`,
`GET_DUMMY1`, `GET_ACCESS`, `GET_HEATS`, `GET_DUMMY2`, `GET_FIRSTAID`,
`GET_BOOTS`.  `GET_MAX`.

`gv.*` weapon indices::
`KNEE_WEAPON`, `PISTOL_WEAPON`, `SHOTGUN_WEAPON`, `CHAINGUN_WEAPON`,
`RPG_WEAPON`, `HANDBOMB_WEAPON`, `SHRINKER_WEAPON`, `DEVISTATOR_WEAPON`,
`TRIPBOMB_WEAPON`, `FREEZE_WEAPON`, `HANDREMOTE_WEAPON`,
`GROW_WEAPON`. `MAX_WEAPONS`.

// TODO: the others, like EVENT_*.
//////////
[[gv_STAT]]
`gv.*` sprite status numbers::
`STAT_DEFAULT`, `STAT_ACTOR`, `STAT_ZOMBIEACTOR`, `STAT_EFFECTOR`,
`STAT_PROJECTILE`, `STAT_MISC`, `STAT_STANDABLE`, `STAT_LOCATOR`,
`STAT_ACTIVATOR`, `STAT_TRANSPORT`, `STAT_PLAYER`, `STAT_FX`, `STAT_FALLER`,
`STAT_DUMMYPLAYER`, `STAT_LIGHT`.
//////////

//////////
`gv.MAXPLAYERS`::
TODO
//////////

Variables
^^^^^^^^^

`gv.numsectors` (read-only)::
The total number of sectors in the currently loaded map.

`gv.numwalls` (read-only)::
The total number of walls in the currently loaded map.

[[totalclock]] `gv.totalclock` (read-only)::
The current value of the engine timer that increments at a rate of 120 per
second under default settings. (Thus, one game tic corresponds to four
`totalclock` increments.) When staying within one ``mode'' such as in-menu or
in-game, it is guaranteed to not decrease. However, going from one mode to
another may produce discontinuities.

`gv.screenpeek` (read-only)::
The player index of the player from whose position the scene is being displayed.

`gv.hudweap`::
A structure containing information about the currently displayed HUD weapon.
Contains the following members, which are set from C before entering
`EVENT_DISPLAYWEAPONS`: `cur`, `count`, `gunposx`, `gunposy`, `lookhalfang`,
`lookhoriz`, `shade`.
// TODO: describe

`gv.cam`::
A structure that, prior to entering `EVENT_DISPLAYROOMS`, is populated with the
position and orientation of the ``camera'' from which the scene would be drawn.
Contains the following members: `pos`, `dist`, `clock`, `ang`, `horiz`, `sect`.
// TODO: describe

// TODO: g_logoFlags, g_RETURN?

Functions
^^^^^^^^^

[[krand]] `gv.krand()`::
Returns one value from the global engine-side pseudo-random number generator
in the range [0{nbsp}..{nbsp}65535].

[[timing_funcs]]
`gv.getticks()`, `gv.gethiticksms()`::
Each of these functions return a number that increases at a rate of 1 per
millisecond. Their only intended application is to profile bits of code; they
should not be used to control the game world. The two functions differ in their
precision: `getticks()` always returns integral values, while the result of
`gethiticksms()` also has an unspecified precision in the fractional part. (It
can be expected to give a time precision of at least one microsecond.)

`gv.doQuake(gametics [, snd])`::
Requests from the game to perform the ``quake'' effect that shakes the screen
etc. for the next `gametics` game tics. If a sound index `snd` is passed, also
start playing that sound.
// TODO: Play sound how? ("globalsound")

//////////
`gv.currentEpisode()`::
TODO
`gv.currentLevel()`::
TODO
`gv.currentRenderMode()`::
TODO
//////////

[[Lunatic_structures]]
Lunatic structures
~~~~~~~~~~~~~~~~~~

The primary means of effecting game state in Lunatic is via _composite
variables_ defined in the global environment. These provide direct, but
restricted, access to C _structure arrays_ of the EDuke32 engine or game.

[icon="icons/din_w_toxic.png"]
CAUTION: If an attempt is made to access any composite variable outside of
event or actor code, the behavior is undefined.

Composite variables can be used in various ways. All of them allow indexing
with an integer value from `0` to some maximum (sometimes the size of the array
minus one, but occasionally less). For example, the code snippet
----------
local sec = sector[0]
----------
gets a _reference_ to the first sector of the loaded map into the local `sec`.
This reference can then be used to both read and write its members.

Various structures also provide _methods_ in Lunatic to modify their state,
usable with Lua's `v:func(args...)` syntax. Building on the previous example,
----------
local cz = sec:ceilingzat(wall[sec.wallptr])
----------
would get into `cz` the ceiling z position at the first sector's first
wall-point.

Finally, some composite variables offer _static data_, which can contain
functions or tables of constants. These are accessed using the dot notation on
the composite variable, *not* its constituents. For instance, the following can
be used to change the sector number of the sprite with index `i` manually:
----------
sprite.changesect(i, sectnum)
----------


Type of structure members
^^^^^^^^^^^^^^^^^^^^^^^^^

In the following, some structure members will be annotated with their _integer
type_, for example _`i16`_ or _`u8`_. The letter _`i`_ denotes a _signed_
integer whereas a _`u`_ designates an _unsigned_ one. The number following that
letter indicates the _bit width_ of that integer.

.Representable values
* A member of signed integer type and bit width _B_ can contain any whole
number from --2^_B_--1^ to 2^_B_--1^--1. +

* A member of unsigned integer type and bit width _B_ can contain any whole
number from 0 to 2^_B_^--1.

[[int_assignment]]
.Assignment
* If an assignment to a member having signed integer type is made, the
  ``right-hand side'' value must be a number in the closed interval
  [--2^31^ .. 2^31^--1].

* If an assignment to a member having unsigned integer type and bit width _B_
  is made, the ``right-hand side'' value must be in the closed interval
  [--2^31^ .. 2^31^--1] if _B_ is less than 32, or in [0 .. 2^32^--1] otherwise.

* If the appropriate requirements hold, an assignment from a Lua number to a
  member having integer type begins by discarding the fractional part
  (``truncation'').  Otherwise, the behavior is undefined. +

* If the truncated value is outside the range of representable values for the
  corresponding integer type of bit width _B_, the final value is obtained by
  successively adding or subtracting 2^B^, until the value falls inside that
  range.

//////////
NOTE to self: this is stricter than C99 (which has first truncation, then range
check). Also, it may be tempting to assign 0x80000000 to an int32_t to mean
INT32_MIN, but this is wrong because it's out of range.
Also see:
http://lua-users.org/lists/lua-l/2011-09/msg00534.html
//////////

.Examples
1. Assignments to _`u8`_ member `visibility`
* `sec.visibility=3.94159` results the member to contain the integer `3`
* `sec.visibility=1/0` is undefined (attempt to assign an infinity)
* `sec.visibility=-1` results the member to contain the integer `255`

2. Assignments to _`i16`_ member `lotag`
* `sec.lotag=32768` results the member to contain `-32768`
* `sec.lotag=2^32` is undefined

Bit fields
^^^^^^^^^^

Some structures contain members that represent a collection of _flags_, for
example `sprite[].cstat` or `actor[].flags`. These flags can be toggled by
setting or clearing their respective _bits_ (integer numbers that are powers of
two).

For convenience, Lunatic provides alternative names for some of these members,
together with methods to examine or modify any number of bits of such a member
in one expression.  Whenever there is such an alternative name available, it is
declared as having type _`bitfield`_ in the listings of the structure members.

===== methods of the _`bitfield`_ type

`bf:set(bits)`::
_Sets_ (toggles to an ``on'' state in a boolean sense) those bits of `bf`
that are set in `bits`.

`bf:clear(bits)`::
_Clears_ (toggles to an ``off'' state in a boolean sense) those bits of `bf`
that are set in `bits`.

`bf:flip(bits)`::
_Flips_ those bits of `bf` that are set in `bits`, that is, reverses their
boolean state.

`bf:test(bits)`::
Returns a boolean that indicates whether `bf` has *any* of the bits set in
`bits` set.

.Examples
==========
After the lines setting sprite `i` to 33% translucent and blocking,
----------
local CS = sprite.CSTAT
local spr = sprite[i]
spr.cstat = CS.TRANS1 + CS.BLOCK
----------
one could proceed as follows for the sake of example:

* `spr.cstatbits:set(CS.TRANS2)`, make the sprite 66% translucent now
* `spr.cstatbits:flip(CS.BLOCK + CS.HITSCAN)`, make it hitscan-sensitive but
  not blocking
* `spr.cstatbits:test(CS.FLIP_BITMASK)`, check whether it is flipped (no)
==========

Engine-side
^^^^^^^^^^^

The composite variables described in this subsection provide access to
engine-side structures. The first three, `sector`, `wall`, and `sprite`,
are part of a BUILD map saved to disk. The other ones only exist when
running the game.

===== `sector`
Accessible from `0` to `gv.numsectors-1`. Each element has the following
members:

`wallptr`, `wallnum` (read-only)::
The index of the sector's first wall and the number of walls in the sector,
respectively.

_`u8`_ `visibility`::
Determines the amount of distance fading. In the range [`0` .. `239`], the
``darkening'' increases with rising values. The range [`240` .. `255`] should
be thought of as [`-16` .. `-1`].
// TODO: better wording?

_`i16`_ `lotag`, `hitag`, `extra`::
General-purpose ``tags'' provided for game programming. They may be used by
various EDuke32 sector effects, so it's not recommended to use them in
scripting code.

In addition to the members described above, each sector has two sets of members
for its ceiling and floor. A sector reference can be indexed with the strings
`ceiling` or `floor` to get references to the respective ``parts'', or one can
access the consituent members by prefixing `ceiling` or `floor` to the base
member names given below.

.Different ways of accessing the same member
==========
After the code lines
----------
local sec = sector[0]
local ceil = sec.ceiling
----------
the following expressions all denote the same location, both if read or written
to: `sec.ceilingheinum`, `ceil.heinum`, `sector[0].ceiling.heinum`,
`sector[0].ceilingheinum`.
==========

In the following, `cf` will stand for a ceiling or floor reference, while `sec`
will label a sector reference.

`cf.picnum` (read-only)::
The tile number of the ceiling or floor.

[[cf_stat]] _`u16`_ `cf.stat`, {nbsp} _`bitfield`_ `cf.statbits`::
A bit field holding various flags about how the ceiling or floor shoud be
displayed, how collision detection should be handled, etc.
The <<sector_STAT,`sector.STAT`>>
object should be used to obtain the values for applicable flags.

_`i16`_ `cf.heinum`::
If `cf.stat` has bit `sector.STAT.SLOPE` set, the tangent of the slope angle
multiplied by 4096.  Positive values make the ceiling or floor slope towards
the floor, negative ones slope upward.

[[cf_z]] _`i32`_ `cf.z`::
The BUILD z coordinate (scaled by 16 compared to the x and y directions) of the
pivoting line of the ceiling or floor.

`cf.bunch` (read-only)::
The ``bunch'' number of the ceiling or floor used for True Room over Room. One
bunch comprises _N_ ceilings and _M_ floors (_N_ &ge; 1, _M_ &ge; 1) such that
each set covers the same planar, connected area.

_`i8`_ `cf.shade`::
The shade of the ceiling or floor. Larger values mean a more darker appearance.

_`u8`_ `cf.pal`::
The ``palette swap'' index of the ceiling or floor.

_`u8`_ `cf.xpanning`, `cf.ypanning`::
The panning values of the ceiling or floor. One full cycle is covered by values
from `0` to `255`.

===== `sector` methods

`sec:set_ceilingpicnum(tilenum)`, `sec:set_floorpicnum(tilenum)`::
Set the tile number of the ceiling or floor.

[[sec_cfz_at]] `sec:ceilingzat(pos)`, `sec:floorzat(pos)`::
Return the z coordinate of sector `sec`'s ceiling or floor at position `pos`,
which can be anything indexable with the strings `x` and `y`.

//////////
`zrangeat(pos, walldist, cliptype)`::
TODO
//////////

===== `sector` static data

[[sector_STAT]] `sector.STAT`::
Provides a mapping of symbolic names to values applicable to
<<cf_stat,`cf.stat`>>.  These name single bits:
`PARALLAX`, `SLOPE`, `SWAPXY`, `SMOOSH`, `FLIPX`, `FLIPY`, `RELATIVE`, `MASK`,
`TRANS1`, `TRANS2`, `BLOCK`, `HITSCAN`, while the following denote _bit masks_:
`FLIP_BITMASK`, `ORIENT_BITMASK`, `TRANS_BITMASK`.

[[sector_UPDATE_FLAGS]] `sector.UPDATE_FLAGS`::
Contains a flag `BREADTH` permissible to <<updatesector,`updatesector`>>.

'''
[[wall]]
===== `wall`
Accessible from `0` to `gv.numwalls-1`. Each element has the following
members:

`x`, `y`::
The 2D coordinates or this wall point. Should not be set directly.

`z` (read-only)::
Always yields `0`. The primary purpose of this field is to make wall references
permissible as arguments to <<vector_types,`xmath` vector>> operations.

`point2` (read-only)::
The index of the second wall point.

[[nextwall]] `nextwall`, `nextsector` (read-only)::
If the wall is ``white'', these members equal `-1`. For ``red'' walls, they
contain the wall and sector indices (respectively) of the wall on the other side.

`upwall`, `dnwall` (read-only)::
For walls constrained by TROR extension, the upper and lower neighbor walls,
respectively. Any of them may be `-1`, meaning that the wall is not attached to
a neighbor in this direction.

[[wall_cstat]] _`u16`_ `cstat`, {nbsp} _`bitfield`_ `cstatbits`::
A bit field holding various flags about how the wall shoud be
displayed, how collision detection should be handled, etc.
The <<wall_CSTAT,`wall.CSTAT`>>
object should be used to obtain the values for applicable flags.

[[wall_picnum]]`picnum` (read-only)::
The tile number of the non-masked portion of the wall. If
`wall.CSTAT.BOTTOMSWAP` is set on this wall's `.cstat`, it is only displayed in
the upper portion. (The lower portion takes it from this wall's `.nextwall`
then; this will be labeled _use-other-bottom_ in the following.)

`overpicnum` (read-only)::
The tile number of the masked portion of the wall, i.e. that which is drawn if
this wall's `.cstat` has bit `wall.CSTAT.MASK` or `wall.CSTAT.ONEWAY` set.

_`i8`_ `shade` (<<wall_picnum,_use-other-bottom_>>)::
The shade of the wall for both non-masked and masked portions. Larger values
mean a more darker appearance.

_`u8`_ `pal` (<<wall_picnum,_use-other-bottom_>>)::
The ``palette swap'' index of the wall.

_`u8`_ `xrepeat`, `yrepeat`::
Values that are proportional to the number of times that the wall's texture
repeats in each direction per given wall length/height. A value of `8` renders
64 texels across a length of 1024 x/y map units or a height of 16384 z units.

_`u8`_ `xpanning`, `ypanning` (<<wall_picnum,_use-other-bottom_>>)::
The panning values of both masked and non-masked portions of the wall. One full
cycle is covered by values from `0` to `255`.

_`i16`_ `lotag`, `hitag`, `extra`::
General-purpose ``tags'' provided for game programming. They may be used by
various EDuke32 effects internally, so it is advised to do some research before
claiming them for oneself.

===== `wall` methods

`wal:set_picnum(tilenum)`, `wal:set_overpicnum(tilenum)`::
Set the tile number of the wall or its masked portion.

===== `wall` static functions

`wall.dragto(i, pos)`::
Set the position of the point of the wall with index `i` to `pos`, which can be
anything indexable with `x` and `y`. This function is the preferred way of
changing wall coordinates, since it takes care to reposition dependent wall
points, too.

===== `wall` static data

[[wall_CSTAT]] `wall.CSTAT`::
Provides a mapping of symbolic names to values applicable to
<<wall_cstat,`wall[i].cstat`>>.  These name single bits:
`BLOCK`, `BOTTOMSWAP`, `ALIGNBOTTOM`, `FLIPX`, `MASK`, `ONEWAY`, `HITSCAN`,
`TRANS1`, `FLIPY`, `TRANS2`,
while the following denote _bit masks_:
`FLIP_BITMASK`, `TRANS_BITMASK`.

'''
[[sprite]]
===== `sprite`

The `sprite` composite is accessible with indices from `0` to
`gv.MAXSPRITES-1`, but accesses to sprites that do not exist in the game world
have no meaning. Each element has the following members:

`x`, `y`, `z`::
The BUILD coordinates of the sprite. It is not advisable to set these directly.

//////////
_`i16`_ `ang`::
TODO (make set_ang() out of that which always ANDs with 2047?)
//////////

[[sprite_cstat]] _`u16`_ `cstat`, {nbsp} _`bitfield`_ `cstatbits`::
A bit field holding various flags about how the sprite shoud be
displayed, how collision detection should be handled, etc.
The <<sprite_CSTAT,`sprite.CSTAT`>>
object should be used to obtain the values for applicable flags.

`picnum` (read-only)::
The tile number of the sprite, also used to determine which _actor_ code is run
if this sprite has a `statnum` of `actor.STAT.ACTOR`.

_`i8`_ `shade`::
The shade of the sprite. This may not be the shade that this sprite is
ultimately drawn with, though.

_`u8`_ `pal`::
The ``palette swap'' index of the sprite. This may not be the palette swap that
this sprite is ultimately drawn with, though.

_`u8`_ `clipdist`::
If this sprite is _view-aligned_, controls the distance at which another moving
object is considered to be in collision with this *stationary* sprite. (It does
not control the inverse case.) More precisely, it designates half the
side-length of the bounding square divided by 4. Thus, a value of `255` keeps
moving objects away from this one at a max-norm distance
footnote:[The max-norm distance between points _p_~1~=(x~1~, y~1~) and
_p_~2~=(x~2~, y~2~) is defined as max(abs(x~2~ -- x~1~), abs(y~2~ -- y~1~)).]
of at least 1020
BUILD x/y units.

_`u8`_ `xrepeat`, `yrepeat`::
The size of the sprite in each dimension. For wall- and floor- aligned sprites,
a value of `64` means a width of 16 x/y BUILD units or a height of 256 z BUILD
units per texel.

`sectnum` (read-only)::
The index of the sector that this sprite is currently contained in.

[[sprite_statnum]] `statnum` (read-only)::
The current _status number_ of this sprite. Applicable values are contained in
<<actor_STAT,`actor.STAT`>>.

`owner` (read-only)::
The index of the sprite from which this sprite was spawned. If this sprite is
not a ``child'' of another one, then `owner` is the index of this sprite itself.
//Occasionally, game effects may use this member for their particular purposes,
//so research is recommended before claiming it for oneself.

_`i16`_ `xvel`, `zvel`::
For _actors_ and other moving sprite types, the horizontal and vertical
components of the current velocity.
//It is not advisable to set these directly
//unless one knows how they are processed.

//`yvel` (read-only)::
//A general-purpose member of which the game has exclusive control.

_`i16`_ `lotag`, `hitag`, `extra`::
General-purpose ``tags'' provided for game programming. They may be used by
hard-coded actors internally, so it is advised to do some research before
claiming them for oneself.

===== `sprite` methods

`spr:set_picnum(tilenum)`::
Set the tile number of the sprite.

===== `sprite` static functions

`sprite.changesect(i, sectnum)`::
Allows to manually change the sector number of the sprite with index `i` to
`sectnum`.

`sprite.changestat(i, statnum)`::
Allows to manually change the status number of the sprite with index `i` to
`statnum`.

===== `sprite` overridden operators

[[sprite_power]] `spr^zofs`::
Returns an <<vector_types,`xmath.ivec3`>> object that contains the position of
this sprite, diminished by `zofs` in the z direction. Because in BUILD, z
coordinates increase toward the floor, the `^` can be thought of as ``raise the
sprite by `zofs` units''.

===== `sprite` static data

[[sprite_CSTAT]] `sprite.CSTAT`::
Provides a mapping of symbolic names to values applicable to
<<sprite_cstat,`sprite[i].cstat`>>.  These name single bits:
`BLOCK`, `TRANS1`, `XFLIP`, `YFLIP`, `ALIGNWALL`, `ALIGNFLOOR`, `ONESIDE`,
`CENTER`, `HITSCAN`, `TRANS2`,
while the following denote _bit masks_: `ALIGN_BITMASK`, `TRANS_BITMASK`.

===== `spriteext`

===== `atsprite`


Game-side
^^^^^^^^^

===== `actor`

The `actor` composite holds various run-time data about a sprite.  Like
<<sprite,`sprite`>>, it is accessible with indices from `0` to
`gv.MAXSPRITES-1`, but accesses to actors that do not exist in the game world
have no meaning.

===== `actor` methods

`a:set_action(act)`::
Sets the action of actor `a` to `act`, which may be either an object returned
by <<con_action,`con.action`>> or a number 0 or 1. Resets the actor's _action
count_ and current frame offset to 0.

`a:has_action(act)`::
Returns a boolean of whether the current action of actor `a` is `act`, which
can be any value permissible to `a:set_action()`. For composite action objects,
equality is established using its hidden ID, not the public members. Refer to
<<actions_moves_ais,Actions&#44; moves and AIs>> for further details.

`a:set_action_delay()`::
Overrides the <<action_delay,`delay`>> of the current action of actor `a`
without changing the action's ID.

`a:set_count(count)`::
Sets the actor's _execution count_ to `count`. The execution count of an actor
increments after each time its <<gameactor,callback function>> has run once.

`a:get_count()`::
Returns the actor's execution count.

`a:reset_acount()`::
Resets the _action count_ of the actor to 0. The action count is incremented on
each frame advance of the actor's current action. Also see the
<<action_delay,`delay`>> argument to `con.action`.

`a:get_acount()`::
Returns the actor's action count.

`a:set_move(mov [, movflags])`::
Sets the move of actor `a` to `mov`, which may be either an object returned by
<<con_move,`con.move`>> or a number 0 or 1. See the <<gameactor_move,`move`>>
argument to `gameactor` for further details. If <<actor_MOVFLAGS,`movflags`>>
is omitted, it defaults to 0.
+
The `set_move` method resets the actor's execution count. Also, if `moveflags`
has bit <<actor_MOVFLAGS,`actor.MOVFLAGS.randomangle`>> set and the actor is
not an enemy or a live enemy, its `sprite[].ang` value is set to a ``random''
value using <<krand,`gv.krand`>>.

`a:has_move(mov)`::
Returns a boolean of whether the current move of actor `a` is `mov`, which can
be any value permissible to `a:set_move()`. Like with `a:has_action()`,
equality is established using the move ID in case a composite one is passed.

`a:set_hvel(hvel)`::
Overrides the <<con_move,horizontal velocity>> of the actor's current move to
`hvel` without changing its ID.

`a:set_vvel(vvel)`::
Overrides the <<con_move,vertical velocity>> of the actor's current move to
`vvel` without changing its ID.

`a:set_ai(ai)`::
Sets the AI of actor `a` to `ai`, which must be an object returned by
<<con_ai,`con.ai`>>. In addition to setting the current AI ID of the actor,
`a:set_ai(ai)` is equivalent to the sequence
+
----------
a:set_action(ai.act)
a:set_move(ai.mov, ai.movflags)
----------

`a:has_ai(ai)`::
Returns a boolean of whether the current AI of actor `a` is `ai`.

// TODO: set_picnum, set_owner?

===== `actor` static functions

`actor.fall(i)`::
Causes the actor with index `i` to fall in a ``hard-coded'', not further
specified fashion.

===== `actor` static data

[[actor_STAT]]
`actor.STAT`::
Provides a mapping of symbolic names to values applicable as sprite
<<sprite_statnum,status numbers>>. +
`DEFAULT`, `ACTOR`, `ZOMBIEACTOR`, `EFFECTOR`, `PROJECTILE`, `MISC`,
`STANDABLE`, `LOCATOR`, `ACTIVATOR`, `TRANSPORT`, `PLAYER`, `FX`, `FALLER`,
`DUMMYPLAYER`, `LIGHT`.

[[actor_FLAGS]] `actor.FLAGS`::
Contains symbolic names of values applicable to <<gameactor,`gameactor`>>'s
`flags` input argument, most of which are described there. +
`SHADOW`, `NVG`, `NOSHADE`, `NOPAL`, `NOEVENTS`, `NOLIGHT`,
`USEACTIVATOR`, `NOCLIP`, `SMOOTHMOVE`, `NOTELEPORT`.

//`BADGUY`,

[[actor_MOVFLAGS]] `actor.MOVFLAGS`::
Contains symbolic names of values applicable <<gameactor,`gameactor`>>'s
`movflags` input argument, `actor[]:set_move()`, and the like. +
`faceplayer`, `geth`, `getv`, `randomangle`, `faceplayerslow`, `spin`,
`faceplayersmart`, `fleeenemy`, `jumptoplayer`, `seekplayer`, `furthestdir`,
`dodgebullet`.

===== `player`

===== `player` methods

`ps:fadecol(fadefrac, r, g, b [, speed [, prio]])`::

Initiates a tinting that linearly fades over time and is blended with the whole
screen contents whenever player `ps`'s view is displayed.footnote:[The behavior
is unspecified should more than one player's view be displayed at one time.]
The first argument `fadefrac` specifies the starting blending coefficient; `r`,
`g` and `b` specify the intensities of the red, green and blue color
components, respectively.
+
Both `fadefrac` and the component intensities are first clamped to the range
[0.0 .. 1.0]. The resulting values are interpreted as a fraction, 0.0 meaning
no blending/no color and 1.0 meaning full blending/full
color.footnote:[Currently, for implementation reasons, a value of 1.0 results
in only _almost_ full blending or presence of the specified color component.]
+
The fourth, optional argument `speed` controls the rate at which the tinting
diminishes. At a value of `1` (the default), a tint with a `fadefrac` of 0.5
finishes in approximately one second.
+
The last, optional argument `prio` must be an integer in the range [`-128`
.. `127`], the default being `0`. When a `fadecol` is issued in the presence of
another tint fading in progress, and the `prio` given by the arriving `fadecol`
is greater or equal than the `prio` of the ongoing one, the latter is canceled
and the arriving fading is initiated in its place. (There is no support for
tint fades that overlap in time.)
+
[icon="icons/din_w_crushing.png"]
CAUTION: If Lunatic code that uses `fadecol` is loaded together with CON code
that writes to the player's `pals` members directly at any point, the behavior
is undefined.

===== `projectile`

===== `g_tile`

===== `g_tile` static data

`g_tile.sizx`, {nbsp} `g_tile.sizy`::
Arrays indexable with tile numbers [`0` .. `gv.MAXTILES-1`] that hold the
horizontal and vertical texel sizes of each tile.


Lunatic functions
~~~~~~~~~~~~~~~~~

Engine-side iterators
^^^^^^^^^^^^^^^^^^^^^

+*for* w *in* wallsofsect(sectnum)+::
Iterates over the indices of all walls of the sector with index `sectnum`.

+*for* s *in* spritesofstat(statnum)+::
Iterates over the indices of all sprites with status number `statnum`.

+*for* s *in* spritesofsect(sectnum)+::
Iterates over the indices of all sprites contained in the sector with index
`sectnum`.

Sector containment functions
^^^^^^^^^^^^^^^^^^^^^^^^^^^^

`inside(pos, sectnum)`::
Returns a boolean of whether the position `pos` (which can be anything
indexable with `x` and `y`) is considered inside the sector with number
`sectnum`, which must be valid. The `z` component is not taken into account.

A number of engine functions take a position `pos` and a starting sector number
`sectnum` and try to find a sector that contains `pos`, assuming it started out
in `sectnum`.footnote:[Note that this is different from CON's `updatesector`,
which takes the starting sector to be the one of the _current sprite_.]

If a valid sector numeric is passed for `sectnum`, these functions first check
whether that sector contains `pos` (i.e. the position stays in the same sector)
and then attempt to search neighboring sectors. If the passed `sectnum` is
`-1`, all sectors are searched in an unspecified order. On success, these
functions return the sector number of the ``updated'' sector, otherwise `-1`.

[[updatesector]] `updatesector(pos, sectnum [, flags])`::

Searches for a sector containing `pos`, which can be anything indexable with
`x` and `y`. Thus, the `z` component is not taken into account. If `sectnum` is
a valid sector number, first all its neighboring walls
(<<nextwall,`wall[].nextwall`>>, ``red wall links'') are searched, falling back
to a linear search on failure.
+
However, this strategy can be problematic if the position passes multiple thin
sectors that overlap another, potentially unrelated sector (for example, in a
TROR or sector-over-sector construction). If such a sector is passed without an
`updatesector` call ever made when it contains the position, the next call may
not find the real sector (as it is now two nextwall links away from the initial
one), and wrongly suggest the overlapping one instead.
+
For this reason, the optional argument `flags` accepts
<<sector_UPDATE_FLAGS,`sector.UPDATE_FLAGS.BREADTH`>>, instructing
`updatesector` to look for matching sectors in a _breadth-first_ search
starting from `sectnum`, and following all nextwall links. With this strategy,
there is *no* fallback to a linear search if no matching sector is found.

`updatesectorz(pos, sectnum)`::

Searches for a sector containing `pos`, which can be any value indexable with
`x`, `y` and `z`. Thus, it additionally takes the `z` component into account by
checking against the bounds that would be returned using a sector's
<<sec_cfz_at,ceilingzat/floorzat>> methods.
+
The `updatesectorz` function first checks the initial sector for containment of
`pos`, then it tries any TROR neighbors of `sectnum`. Finally, it proceeds like
`updatesector` as far as the searching order is concerned.

//////////
cansee
hitscan
neartag
sectorsofbunch
//////////

Customizing the game
^^^^^^^^^^^^^^^^^^^^

In Lunatic, there are two main ways of customizing the game's behavior. Both
involve the user providing functions that are _called back_ at certain points
in the execution of EDuke32. Game _actors_ are simply sprites that run a
particular piece of code based on their tile number each game tic, unless they
are in a ``dormant'' state. Game _events_ are invoked at predetermined points
in the program flow.

To register custom actor and event code with the game (and define additional
actor information), Lunatic provides two functions in the global environment,
`gameactor` and `gameevent`. As their sole argument, they take a table
containing the appropriate data.

[[gameactor]]
===== The function `gameactor{tilenum [, ...], func}`

Registers custom code for the actor given by tile number `tilenum`. For each
non-sleeping actor, the function `func` is called every game tic with three
input arguments: `func(aci, pli, dist)`.

* `aci`: the sprite number of the actor invoking `func`
* `pli`: the index of the player that is nearest to this actor
* `dist`: the 3D Manhattan distance
  footnoteref:[mhdist_def,The Manhattan distance between points
  _p_~1~=(x~1~&#44; y~1~&#44; z~1~) and _p_~2~=(x~2~&#44; y~2~&#44; z~2~) is
  defined as abs(x~2~ -- x~1~) + abs(y~2~ -- y~1~) + abs(z~2~ -- z~1~).]
  between actor `aci` and player `pli`

// NOTE: &#44; is the comma; the footnote would be truncated at it otherwise.
// For a related issue, see
// http://www.methods.co.nz/asciidoc/faq.html#_why_am_i_having_trouble_getting_nested_macros_to_work

Additionally, `gameactor` accepts optional input arguments. They can be
specifyed positionally by following `tilenum`, or be given as values to string
keys of the argument table. Each such input argument may be provided in at most
one of these two forms. Furthermore, `func` may be provided as value to the
key `'func'` as well.

`[2] flags`::
A number that controls both certain aspects of the `gameactor` call as well as
the run-time behavior of the actor itself. A couple of bits for the latter type
are listed in <<actor_FLAGS,`actor.FLAGS`>>, abbreviated `AF` in the following.
+
These values describe the ``type'' of the actor: `AF.enemy`, `AF.enemystayput`
and `AF.rotfixed`. Except for `enemystayput`, they name single bits
(`enemystayput` implies `enemy`).
+
In Lunatic, game actors can be _chained_, that is, a callback function can be
either appended to the end of an already registered one, or prefixed at its
front. In this case, a previous `gameactor` call must have taken place for that
actor (this may have happened from a CON `useractor` block, which gets
translated to `gameactor`). Moreover, this mechanism allows to add run-time
flags to the actor in question.
+
Several flags in `AF` are provided to control how a `gameactor` invocation
handles chaining.
+
* `AF.replace_hard`: Completely replace the actor's callback function and
  run-time flags. This is the default.
* `AF.replace_soft`: Replace the callback function, but bitwise-OR the existing
  run-time flags with the provided ones. This is the way CON's `useractor`
  behaves.
* `AF.chain_beg`: Prepend the provided `func` to the exising callback function,
  bitwise-OR in flags.
* `AF.chain_end`: Append the provided `func` to the exising callback function,
  bitwise-OR in flags.
+
The following members all default to 0 if omitted.
+
`[3] strength`::
The initial strength or health of the actor.

`[4] action`::
The initial action of the actor. May be either an object returned by
<<con_action,`con.action`>>, or the numbers 0 or 1. Both represent actions with
that ID, but all public members set to 0.

[[gameactor_move]] `[5] move`::
The initial move of the actor. May be either an object returned by
<<con_move,`con.move`>>, or the numbers 0 or 1. Both represent moves with that
ID, but all public members set to 0. A move of 0 disables the usual actor
movement, even if its `hvel` or `vvel` get subsequently overridden (and the
corresponding `movflags` set).

`[6] movflags`::
The actor's initial movement flags. Applicable bits are available in the
<<actor_MOVFLAGS,`actor.MOVFLAGS`>> object.

===== The function `gameevent{evtlabel [, flags], func}`

:wiki: http://wiki.eduke32.com
:wiki_eventlist: http://wiki.eduke32.com/wiki/EDuke32_event_list

Registers custom code to be run at specific points in the program.  The first
argument `evtlabel` should be a string naming the event. A complete
{wiki_eventlist}[list of events] can be found at the {wiki}[EDuke32 wiki]. The
label may be stripped of the leading ```EVENT_`'', so that e.g. `EVENT_JUMP`
and simply `JUMP` denote the same event.

The arguments `flags` and `func` can alternatively be passed as values to the
same-named keys of the input argument table to `gameevent`. Like with
`gameactor`, each may be provided in at most one of the two forms.

The callback `func` is invoked with the same arguments and meaning as for
<<gameactor,`gameactor`>>, but certain events are run in contexts where no
meaningful `aci` and/or `pli` value can be assigned. In this case, `func`
receives `-1` for the respective input arguments.

Like with actors, game events may be chained or replaced by passing an
appropriate `flags` value. However, it is not necessary for an event to be
already defined when chaining is requested. In that case, it is simply
registered initially.  Permissible values for these flags are provided in
`actor.FLAGS` as well (abbreviated `AF` here):

* `AF.replace`: Replace any previously defined event code with the given one.
* `AF.chain_beg`: Prepend the provided `func` to the exising callback
  function. This is the behavior of CON's `onevent`.
* `AF.chain_end`: Append the provided `func` to the exising callback
  function. This is the default.

// TODO: RETURN handling...


[[ext_api]]
Extended API (Lunatic modules)
------------------------------

The `xmath` module
~~~~~~~~~~~~~~~~~~

Mathematical functions
^^^^^^^^^^^^^^^^^^^^^^

Lunatic, being a Lua-based scripting system, provides the user with a single
numeric data type that variables can contain on the Lua side --
double-precision floating point.footnote:[In LuaJIT, variables additionaly can
take on ``boxed'' 64-bit integer numeric types, but these should not be used
for numeric calculations.]  However, since BUILD, and in turn, EDuke32, almost
exclusively use integer types to represent quantities such as angles or carry
out e.g. trigonometrical calculations, there is a need for convenient
interoperability between the two ``worlds''.

Two pairs of functions calculate the trigonometric sine and cosine, both
accepting a BUILD angle as input argument, but differing in the scaling of
their result. Using these functions is recommended over Lua's `math.sin` or
`math.cos` in cases where the argument is a BUILD angle in the first place, for
example because it is read from an engine or game structure. The computation is
both faster (because it is essentially only a bitwise-AND operation followed by
a table lookup) and the results have the symmetry expected from the
mathematical counterparts.

`xmath.sinb(bang)`, {nbsp} `xmath.cosb(bang)`::
Returns the sine/cosine of the given BUILD angle `bang`, which can be any
whole number in [--2^31^ .. 2^31^--1]. In BUILD, one full cycle is covered by
values from 0 to 2047; in other words, an angle of 2048 corresponds to 360
degrees.
+
The `sinb` and `cosb` functions return values in the range [--1 .. 1], just
like their mathematical counterparts.
+
The following guarantees are made for `sinb` whereever its argument expression
is permissible:
+
* `sinb(-a) == -sinb(a)` (point symmetry around the origin)
* `sinb(a + i*2048) == sinb(a)`, where `i` is any whole number (periodicity)
* `sinb(1024 - a) == sinb(a)` (mirror symmetry around `a`=512)
* `sinb(a - 1024) == -sinb(a)` (point symmetry around `a`=1024)
* The value for `cosb(a)` is derived as `sinb(a + 512)`.

`xmath.ksin(bang)`, {nbsp} `xmath.kcos(bang)`::
Returns the sine/cosine of the given BUILD angle `bang`, multiplied with 16384
and rounded towards zero. The same guarantees as for the `sinb`/`cosb` pair
apply.

`xmath.dist(pos1, pos2)`::
Returns an approximation of the 3D Euclidean distance between points `pos1` and
`pos2`, both of which can be any object indexable with `x`, `y` and `z`.
<<cf_z,BUILD z units>> are assumed.

`xmath.ldist(pos1, pos2)`::
Returns an approximation of the 2D Euclidean distance between points `pos1` and
`pos2`, both of which can be any object indexable with `x` and `y`.

[[vector_types]]
The types `xmath.vec3` and `xmath.ivec3` [_serializeable_]
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Another purpose of the `xmath` module is to provide _vector_ types that allow
writing concise and clear code involving geometrical calculations. There are
two types, both containing three components (`x`, `y` and `z`), but differing
in their numeric type. For the most part, `vec3` should be used, whose
components are Lua numbers, i.e. floating point. The other type, `ivec3`, is
part of some game structures, and consequently uses 32-bit integers for its
components. With minor differences, the `vec3` and `ivec3` types share the same
operations and methods.

The constructors of the vector types can be called in several ways. In the
following, they are only described for `vec3`. The conventions for `ivec3` are
completely analogous, but since their creation involves a number type
conversion, the rules about <<int_assignment,assignment to integer types>>
apply.

`v = xmath.vec3([x [, y [, z]]])`::
Create a 3-element vector `v` by passing the `x`, `y` and `z` components
separately. Trailing components can be omitted, in which case they are
initialized to 0.

`v = xmath.vec3(t)`::
Create a 3-element vector `v` by passing `t`, which can be any variable
indexable with the strings `x`, `y` and `z` (and yielding numbers for these
lookups). For example, `t` can be another (`i`)`vec3`, a `sprite` or even
<<wall,`wall`>> reference, as each of them can be indexed with these three
keys.

Since the vector types are compound objects, they are always passed around by
reference. For example, consider executing
----------
v = xmath.vec3(0, 1)
w = v
w.y = 2
----------
After this code, the expression `v.x` yields `2` instead of `v`'s initial value
`1`.

===== Operations for `vec3` and `ivec3`

In the following, `v` denotes a `vec3` or `ivec3` object reference while `t`
denotes any object indexable with `x`, `y` and `z`. Note that for binary
operations, Lua looks for overridden operators in the left operand first and
the right one next.  So, where `t` appears on the left hand side of an
arithmetic expression, it is assumed that `t`'s type does not overload the
corresponding operation or provides the same semantics. Arithmetic operations
always return a (reference to a) new `vec3` object, even if any or both of the
operands have `ivec3` type.

`v + t`, {nbsp} `t + v`::
Returns a new `vec3` object whose components are the sum of the respective
components of `v` and `t`.

`v - t`, {nbsp} `t - v`::
Returns a new `vec3` object whose components are the difference of the
respective components of `v` and `t` (in the first case) or `t` and `v` (in the
second case).

`-v`::
Returns a new `vec3` object with the components of `v` negated.

`a*v`, {nbsp} `v*a`::
For a scalar number `a`, returns a new `vec3` object whose components are those
of `v` mutiplied with `a`.

`v/a`::
For a scalar number `a`, returns a new `vec3` object whose components are those
of `v` divided by `a`.

`v^zofs`::
Returns an object of the same type as `v` and with the same components, except
that `v.z` is diminished by `zofs`. Also see the <<sprite_power,power
operation>> for `sprite` objects.

`tostring(v)`::
Returns a string representation of `v` for display purposes: ```vec3`'' or
```ivec3`'', followed by the components of `v` in parentheses.

===== Methods for `vec3` and `ivec3`

`v:len()`::
Returns the Euclidean length of `v` in three dimensions.

`v:lensq()`::
Returns the squared Euclidean length of `v` in three dimensions.

`v:len2()`::
Returns the Euclidean length of `v`, taking only the `x` and `y` components
into account.

`v:len2sq()`::
Returns the squared Euclidean length of `v`, taking only the `x` and `y`
components into account.

`v:mhlen()`::
Returns the length of `v` calculated using the Manhattan distance
footnoteref:[mhdist_def] in three dimensions between the origin and the
endpoint.

`v:toivec3()`::
Returns a new `ivec3` object with the same components as `v`, but converted
<<int_assignment,to integers>>.

`v:touniform()`::
Returns a new vector of the same type as `v` which has the same `x` and `y`
components as `v`, but the `z` element divided by 16 (if `v` is a `vec3`) or
arithmetically right-shifted by 4 (if `v` is an
`ivec3`).footnote:[Right-shifting by 4 can be seen as a division by 16 with
subsequent rounding to an integer towards negative infinity.] Also see the
description of the ceiling/floor <<cf_z,`z` member>>.

`v:tobuild()`::
Returns a new vector of the same type as `v` which has the same `x` and `y`
components as `v`, but the `z` element multiplied with 16.


The `con` module -- game control
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The `con` module on one hand provides functionality to control certain aspects
of the game, such as defining game-side animations for actors. On the other
hand, it hosts varioius functions that are familiar from CON, although
sometimes under a different name.

[[actions_moves_ais]]
Actions, moves and AIs -- customizing actor behavior
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

In CON, three aspects of an actor can changed using a mechanism that is
syntactically similar for each. _Actions_ carry information about a particular
animation for an actor, such as how many frames it contains. _Moves_ define the
potential motion characteristics of an actor. Finally, _AIs_ are aggregates of
an action and a move, plus _movement flags_ that toggle certain movement
aspects.

At file scope, one first defines each of these composites using directives such
as `action`, and inside code blocks to be executed at game time, one instructs
the game to use a particular composite by passing the chosen label to the
same-named command (i.e. `action` for our example).

Lunatic provides a similar mechanism, but the main difference from CON is that
the definition functions merely return the composite structures, without
registering them under any particular name. Thus, it is up to the user to
organize them, for example by storing those for each class in a separate table
indexed by chosen names. Similar to CON, the creation functions may only be
called when the game is not yet running.

Actor behavior composites contain an additional ``hidden'' ID. Each invocation
of a creation function such as `con.action` returns a composite with a unique
ID per composite type. This ID is used to compare for equality in actor methods
such as `actor[]:has_action()`. All returned composites are immutable.

[[con_action]]
===== The function `con.action{ ... }`

:wiki_action: http://wiki.eduke32.com/wiki/Action
:Lua51_TableConstructors: http://www.lua.org/manual/5.1/manual.html#2.5.7

Returns a new _action_ composite created with the given values. The
`con.action` function expects a single table as input argument, each of whose
keys denote an action member. Each member may be provided by an index in the
table or its name, but not both. Members may be omitted, in which case they
default to either 0 or 1.

Refer to the {Lua51_TableConstructors}[Table Constructors] subsection of the
Lua 5.1 Reference Manual for the syntax and semantics of table initialization.

`[1] startframe`::
The offset of the starting frame of the animation, relative to the
`sprite[].picnum` of an actor (i.e. the tile number, selecting which actor code
is run).

`[2] numframes` (default: 1)::
The total number of frames in the animation.

`[3] viewtype` (default: 1)::
The number of consecutive tiles used to construct one frame of the animation,
as viewed from different angles. Valid values are 1, 3, 5, 7 and 8. In
addition, -5 and -7 are allowed, which behave like the corresponding positive
++viewtype++s, but effectively mirror the actor on the vertical axis. This can
be useful if tile data is available that has the opposite orientation of what
EDuke32 uses.  See the {wiki_action}[Action entry] in the EDuke32 wiki for how
the views are constructed for different `viewtype` values.

`[4] incval` (default: 1)::
The value to add the actor's _current frame_ on each frame advance. May be -1,
0, or 1.
// In the wild, sometimes other values, too.

[[action_delay]] `[5] delay`::
Roughly, the number of <<totalclock,`gv.totalclock`>> time units (120 per
second) after which a frame is advanced, at a granularity of one game tic (30
per second, corresponding to a `delay` difference of 4).footnote:[The reason
for the granularity is due to the implementation: each execution of an actor's
code increments its hidden ``action tics'' counter by four (= 120/30).]

// TODO: the above can be more precise. State in terms of floor(delay/4).

.Equivalent `action` definitions
==========
Each of the following calls return an action with the same public members:
----------
con.action{0, 4, delay=20}
con.action{0, 4, 1, 1, 20}
con.action{startframe=0, numframes=4, viewtype=1, incval=1, delay=20}
----------
==========

[[con_move]]
===== The function `con.move{ ... }`

Returns a new _move_ composite created with the given values, expecting a
single table as input argument. The same conventions as with `con.action` apply
for the following members:

`[1] hvel`::
The (most often) doubled horizontal velocity of the actor, in BUILD x/y units
per game tic. An actor's `sprite[].xvel` will approach this value in an
``exponential'' fashion, halving the difference between the current velocity
and this goal velocity each movement update from the actor execution loop. For
most objects, `sprite[].xvel` is then further halved to yield the ultimate
velocity. Only effective when the actor's `movflags` has
<<actor_MOVFLAGS,`actor.MOVFLAGS.geth`>> is set.

`[2] vvel`::
The (most often) doubled horizontal velocity of the actor, in BUILD x/y (*not*
z) units per game tic. An actor's `sprite[].zvel` will approach 16 times this
value in an ``exponential'' fashion. For most objects, `sprite[].zvel` is then
further halved to yield the ultimate velocity.  Only effective when the actor's
`movflags` has <<actor_MOVFLAGS,`actor.MOVFLAGS.getv`>> is set.

[[con_ai]]
===== The function `con.ai([action [, move [, movflags]]])`

The `con.ai` function differs from `con.action` and `con.move` in that it is of
``second order'', i.e. it accepts two composites as input arguments, returning
an _AI_ object containing these. Also, it is called with three positional,
optional arguments. Like for <<gameactor,`gameactor`>>, the numbers 0 and 1 are
permissible for `action` and `move`. Applicable bits for `movflags` are
available in the <<actor_MOVFLAGS,`actor.MOVFLAGS`>> object.