Three events get a sound: a shot leaving a gun, a vessel dying, a structure
coming down.
The sounds are SYNTHESISED rather than downloaded - audio/make_sfx.py
generates all three from scratch, and is committed alongside them. The
ticket asked for free sources and the good ones are in its comments
(Kenney's CC0 packs, OpenGameArt's CC0 sets, Freesound filtered to CC0),
but a generated sound has no licence to track, no attribution to keep, and
no binary in the repository whose provenance nobody can check a year from
now. It also makes the sounds DATA: too sharp a shot is a number in that
file and a re-run, not a hunt through a library. Dropping in a pack file
later means replacing a .wav and nothing else.
A voice POOL, not a player, because these overlap constantly - a fleet
firing is several shots inside one shot's length. Twelve voices, and when
they are all busy the one furthest through its own sound is recycled, which
is the one with the least left to lose.
Parented to the tree root, for the reason that matters: every one of these
sounds is started by something that is being freed on the same frame. A
dying ship cannot own the sound of its own death.
Levels are per sound rather than shared - a shot fires constantly and a
death happens once, so equal volumes are not proportionate ones - and shots
get a little pitch spread so a stream of them does not flatten into one
machine-gun note. The deaths get none: a wobbling explosion sounds broken
rather than varied.
The test goes at the failures a play-through would hide for weeks: firing
three times the pool size must leave exactly the pool's worth sounding and
no leaked voices, and the ship-death case is checked from a node that really
has been freed on that frame.
"All the time" is the whole of the requirement and it decides the shape.
The theme has to survive the main menu becoming the game, the game becoming
a planet surface, and the surface becoming the game again - so the player
cannot live in any of those scenes, because change_scene_to_file() frees
whichever one is current.
It is parented to the tree root instead, beside the GameState autoload,
which is the same trick for the same reason. Music.ensure() is idempotent by
node name, so each scene asks for the music on the way up and gets the one
already playing rather than a second copy over the top of it. Two call
sites cover everything: MainMenu, and GameController - which is the root
script of BOTH the space scene and the planet surface.
Done this way rather than as an autoload deliberately: project.godot carries
the developer's own uncommitted window settings, and adding music should not
drag those into a commit.
It is also PROCESS_MODE_ALWAYS. Since #128 a dialog stops the tree, and a
soundtrack that cuts out every time someone reads a line is worse than no
soundtrack.
The theme ships as MP3 rather than the 59MB WAV that was sitting in the
project root. Same 5m36s, 6.7MB, encoded with LAME at 160k - 89% smaller,
which is the difference between a repository that carries its music and one
that carries a WAV forever in its history. The original file is untouched
and still there, untracked, so nothing is lost.
The test checks CONTINUITY rather than "a sound started": the same player,
never a second one, through two scene changes and a dialog.
