Beatbound

Cinevva's analyzer read this game's design doc and its source, then wrote the brief below. "Make your own" hands it to the game creator as your opening message, so you start from a real spec rather than a one-line idea.

Create a single-screen 2D canvas rhythm endless runner titled “Beatbound.” Use a full-window responsive canvas with no scrolling page, dark navy futuristic neon styling, and crisp geometric shapes rendered with simple fills, gradients, glow, and translucent overlays.

Core gameplay: the player controls a small glowing cyan rounded-square character fixed horizontally at about 24% of the screen width, running automatically across a ground track. The objective is to survive as long as possible by jumping over incoming rectangular obstacles while timing jumps to the beat. The game runs at 112 BPM, with a beat every 60/112 seconds and a generous timing window of 0.18 seconds on either side of each beat. A jump input is only accepted while the player is grounded. If pressed within that beat window, perform a stronger/standard jump (initial vertical velocity about 700), award points equal to 10 plus 2 times the newly increased combo, increment the combo, briefly flash cyan particles and show “PERFECT” or “PERFECT xN” feedback. If pressed off beat, still jump (initial velocity about 610), reset the combo, show “OFF BEAT” in orange, and play a lower error tone. Do not allow double jumps. Apply gravity around 1700 so the character arcs up and returns to the track.

The player’s horizontal position remains fixed while obstacles move from right to left. Start spawning after roughly 0.6 seconds, then spawn obstacles at intervals of either 1.5 or 2 beats, with a 25% chance of the shorter interval. Each obstacle begins just beyond the right edge, has a random width around 36–58 pixels and height around 38–76 pixels, and is removed after leaving the screen. Most obstacles (about 78%) are beat-associated and should be pink/red (#ff4d8d); the remainder should be orange (#ffae57). Draw them as rounded rectangles with a small pale highlight bar near the top. Collision occurs when the obstacle overlaps the player’s fixed x range and the player is not high enough to clear the obstacle. On collision, end the run immediately, save the high score in local storage under “beatbound-best,” and play a low game-over tone. Increase travel speed over time from about 290 pixels/second up to a cap increase of 150, using approximately 290 + min(150, elapsed seconds*7), making the run progressively harder.

The track sits at 76% of viewport height. Draw a dark blue ground rectangle from the track to the bottom, with a bright 4-pixel cyan top edge. Add a thin vertical cyan “center line” at approximately 68% of the viewport width, extending 170 pixels upward from the track; its opacity and the beat pulse brighten on each beat. The visual instruction refers to timing the jump when the pulse hits this center line, although the player remains fixed and obstacles travel toward it. Use a scrolling perspective grid behind the track: faint diagonal lines from the horizon around 58% height toward the bottom and horizontal lines every 34 pixels, with the grid’s horizontal offset advancing with run speed and wrapping every 64 pixels.

Background: fill the whole screen with a vertical gradient from #111936 at the top to #070912 at the bottom. Add a faint blue circular glow around 72% width and 22% height that expands/brightens on beats. Beat pulses should decay smoothly, and the beat pulse should also influence the center line and background glow. Add brief cyan square particle bursts around the player’s ground position on perfect jumps; particles drift outward and upward, then fall slightly and fade.

HUD during every state: top-left display “BEATBOUND” in bold light text, then “SCORE [number]” and “BEST [number]” below it. Top-right display “112 BPM.” During play, show centered feedback around 20% screen height: perfect feedback in cyan and off-beat feedback in orange. Use a clean system sans-serif font, with light gray-white primary text and muted periwinkle-blue secondary text.

States and controls: begin in a menu state. The menu has a translucent dark overlay and centered title “BEATBOUND,” subtitle “A RHYTHM RUNNER,” instructions split over two lines as “Jump when the pulse hits” and “the center line.”, and a bordered dark rounded button reading “TAP TO START.” At the bottom show “Space / tap / click.” A pointer/touch press on the canvas, or keyboard Space, ArrowUp, or W, starts the game. Starting resets score, combo, obstacles, particles, timing, speed, and player jump state, and initializes Web Audio. While playing, the same inputs attempt a beat-timed jump. On collision show a game-over overlay with title “RUN OVER,” “SCORE [score],” the same two-line instruction, and a button reading “TAP TO RETRY”; the same controls restart. Keep the canvas touch-action disabled and prevent default input behavior.

Audio: on first interaction create/resume a Web Audio context. Schedule a repeating synthesized beat at 112 BPM: a stronger low sine tone on every fourth subdivision (about 110 Hz, 0.16 sec, volume about 0.09), a short square tone around 660 Hz on odd subdivisions, and a shorter 220 Hz square tone on other subdivisions. Also play a triangle success tone whose pitch rises with combo (starting around 520 Hz, capped combo contribution around 10), a short sawtooth error tone around 170 Hz for off-beat presses, and a low sawtooth tone around 90 Hz on game over. Keep the experience minimalist and arcade-like, with no invented characters, weapons, lives, levels, collectibles, or extra screens.