com.harryaskham.orbitdrums · Kotlin · OpenGL ES 3 · sounds by chirp

Orbit Drums

A drumming game in polyrhythms, played with two thumbs, a game controller or a keyboard. Every lane is an orb: a circular drum whose arm sweeps once per bar, in lock-step with the others. An orb that divides the bar into three carries a triangle of notes, four a square and five a pentagon, and you strike each note as the arm crosses it.

23 levels in 6 worlds6 bosses6 lessons±38 ms perfect

Overclock on Hard, played perfectly. The Neon boss runs from 4/4 into 7/8, 11/8 and back to 4/4. The game recorded its own frames while its autoplay struck every note, and its own mixer rendered the music underneath.

Orbs

Drawn from the level's definition in Catalog.kt, so it changes when the level does.

Notes come in several kinds: strikes, accents, holds, rolls, flicks (a swipe up), ghost notes you may skip (on Hard they become ordinary strikes), and voids, where you must stay silent. Notes that land at the same instant on different orbs are conjunctions, and filling the Resonance meter ignites it on the next downbeat.

Songs are built in sections, and a section can change the music under you: it can turn the orbs into different shapes, run the arms backwards, hide an orb, ramp the tempo or change the meter.

Controls
Orbs	Controller	Keyboard
Two	L1, L2, D-pad · R1, R2, A B X Y	`D` `F` · `J` `K`
Three	adds L2 and R2 for the middle orb	adds `Space`
Four	split across both shoulders and pads	`S` · `D` `F` · `J` `K` · `L`

Six worlds

Each world has its own key, instruments, background and a mechanic it introduces. Landed strikes leave each world's mark: moon dust, sand, laser streaks, petals, bubbles or bent light.

Hemiola on Luna: a triangle orb and a two-note line orb under a moonlit sky, notes and approach rings on their rims. — **Luna**Hemiola · 3:2 · kalimba, handpan, glass, music box

Bembé on Dune: a square orb against a six-pulse orb over dusk dunes, sand bursting from struck notes. — **Dune**Bembé · 4:6 · tabla, koto, tanpura, hand percussion

Overdrive on Neon: two orbs over a striped synthwave sun and a scrolling grid, a combo multiplier at the top. — **Neon**Overdrive · 4:3 · 909 kit, supersaw, acid bass, arps

Temple of Bells on Gilded: three orbs over a gold mandala, petals falling from struck notes. — **Gilded**Temple of Bells · 3:5:4 · gamelan, glockenspiel, vibes

Sonar on Abyss: a four-pulse orb and a seven-pulse orb in deep teal water, the Voids section card between them and red void notes on the rim. — **Abyss**Sonar · 4:7 · sub bass, reese, dub kit, voices

Singularity on Horizon: four orbs in a row over an accretion disc, the finale's arms sweeping together. — **Horizon**Singularity · 3:4:5:7 · electro kit, ondes, choir

The Journey, read from `Catalog.kt` and `World.kt` when this page was built
World	Key	Levels	Orbs	BPM	Boss
Luna	D major	5	1–2	80–96	The Tidewarden
Dune	D Hijaz	4	2	100–138	Simoom
Neon	A minor	4	2–3	108–124	Overclock
Gilded	E pelog	4	2–3	84–96	Kala
Abyss	F minor	3	2	72–80	Kraken
Horizon	C Dorian	3	2–4	96–104	Event Horizon

Bosses in odd time

Clearing a world opens its boss. Bosses move through odd and shifting meters. Before each change a card slides in with the new time signature and its beat groups, then bursts on the downbeat. An orb that follows the groups (2+2+3 in 7/8) draws an irregular polygon through the group starts, and arcs around its rim mark each group.

Every landed strike drains the boss's health; PERFECTs and conjunctions hit hardest. A boss must be broken before the song ends, because one that survives is a fail. Each boss brings its own band, from djembe and sitar to gong and waterphone, and breaking it plays a fanfare.

The Tidewarden, a great almond eye, between two orbs; the health bar at the top. — **The Tidewarden**Luna · 4/4 → 5/4 → 7/8

Simoom, a spinning sand vortex, between two orbs in 7/8 over the dunes. — **Simoom**Dune · 3/4 → 7/8 → 9/8

Overclock breaking: its name glitches across the Neon sun as red shards and a shockwave burst between the two orbs. — **Overclock**Neon · 4/4 → 7/8 → 11/8

Kala, a gold idol in a ring of turning petals, between orbs in 11/8. — **Kala**Gilded · 5/8 → 11/8 → 13/8

The Kraken, a dark mantle with one amber slit-pupilled eye and eight banded arms, in deep water between two orbs. — **Kraken**Abyss · 9/8 → 7/4 → 15/8

Event Horizon, a black hole with a glowing disc, behind a row of four orbs. — **Event Horizon**Horizon · 4/4 → 11/8 → 15/8 → 7/8

Modes

Journey: levels across six worlds, each with Easy, Normal and Hard charts, and a final level that unlocks at 60 stars.
Bosses: one per world, in odd and shifting meters such as 7/8 and 11/8, with health your strikes drain before the song ends.
Orbit School: short lessons in striking, holding, two hands, conjunctions, flicks and voids, each looping until you get it.
Daily: one seeded song a day, with a name, a streak and sometimes a twist such as Mirror or Fade; about one day in four is in an odd meter.
Endless: two to four orbs drifting through ratios, faster and denser as you go.
Workshop: any ratio from 1:1 to 9:9 at 40–160 BPM, optionally with the computer playing one hand.
Jam: free play over a world's backing with a loop recorder; loops can be shared as a link or exported as a WAV file.

The title screen: ORBIT DRUMS over a striped synthwave sun, 58 of 90 stars, and a menu of Continue, Journey, Daily, Endless, Workshop, Jam and Settings. — **Title**the backdrop tours the worlds you've opened

The Horizon journey map: level sigils joined by a path with stars under each, then Event Horizon and the final level, Musica Universalis, locked until 60 stars. — **Journey**each world's path ends at its boss

Overclock's level sheet over the Neon map: 4/4 to 7/8 to 11/8 at 124 BPM, Easy, Normal and Hard, and its mechanics with the new ones marked. — **Level sheet**difficulty, records and what's new

Orbit School, lesson 1 of 6, Strike: tap the orb as the arm crosses each note, with a ring on the next note and six progress dots. — **Orbit School**six lessons that loop until you get them

Jam at 3:4: two orbs over the Neon sun, with record, 1, 2 and 4 bar loops, Clear, Save, Link and WAV. — **Jam**loops save, share as links and export as WAV

Results for Overdrive on Hard: an S+ seal whose rings plot every strike, 100% accuracy, 340 PERFECTs and 52 of 52 conjunctions. — **Results**every strike plotted around the bar

Timing

Read from Session.kt. A close-up of one note above, and one whole bar to scale below.

Calibration is tapping along with a click. Offsets are kept separately for each audio output (the speaker, wired headphones, and each Bluetooth or USB device by name), and calibrating with a controller measures that controller's own extra delay. On a controller or keyboard, flick notes strike themselves.

Sound and picture

The game's 44 instruments are rendered ahead of time with chirp, the synthesiser on the tools site, into Ogg sample banks shipped in the app (about 6 MB), and played by a sample-accurate mixer. The band grows with your combo: extra parts join at 10 and 30, every 16 PERFECTs in a row plays a run, and conjunctions ring a chord. Each world's sounds are decoded once and cached, so only the first play of a world waits for decoding.

The picture is drawn with OpenGL ES 3.0. The game logic (charts, judging, worlds, the composer, the mixer and the generators for daily, endless and workshop songs) is a plain Kotlin module with its own tests, including an autoplay of every level on every difficulty to a perfect result.

Limits

Timing depends on the audio output's delay; each output needs calibrating once.
The final level, Musica Universalis, stays locked until you have 60 stars.
Android only, through Google Play internal testing.