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 polished mobile/desktop 2D side-scrolling rhythm runner titled “Beatbound.” Use a full-screen responsive HTML canvas with a dark neon aesthetic: a deep navy-to-near-black vertical gradient background, a large soft purple circular glow centered high in the playfield, subtle perspective/grid lines receding toward the horizon, and a dark indigo ground occupying the bottom quarter with a thin blue-violet top edge. The camera is fixed side-on; the world scrolls from right to left while the player stays around 22% of the screen width.

The player is a small glowing aqua/turquoise rounded square character (about 36px square on a typical viewport) on the ground, with a dark single circular eye/detail near its upper-right. Give it a soft cyan bloom and a subtle squash/stretch when jumping. Gravity pulls it back down after each jump. The jump is a single fixed-height hop and can only be initiated while grounded.

Make the core mechanic rhythm-based. The track runs at exactly 120 BPM (one beat every 0.5 seconds), with a visible beat indicator: a small outlined circle near the top-center that briefly expands and brightens on each beat, then fades. Also play simple synthesized tones: a stronger low triangle tone on every fourth beat and a lighter higher tone on other beats. Spawn a glowing pink/magenta vertical neon gate roughly every four beats, beginning after the opening beats. Gates enter from the right at x about 112% of screen width and travel left toward the player. Each gate is a narrow rectangle around 6.5% of screen width and 16–23% of screen height, sitting on the ground; add a small pale highlight stripe near its top and a strong pink glow. Increase scroll speed slightly as score grows, capped at the modest amount implied by the original mechanics.

Controls: clicking/tapping the canvas, pressing Space, ArrowUp, or W, or using a mobile “JUMP ON BEAT” button performs the jump. Ignore jump input while airborne. Judge timing against the nearest point in the current 0.5-second beat interval: a jump is “on beat” if within 0.16 seconds of a beat boundary, including just before or after it. On-beat jumps use a higher jump velocity, increment the combo, award 100 plus 10 times the new combo, play an ascending square-wave confirmation tone, and emit a cyan particle burst. Off-beat jumps use a slightly lower jump velocity, reset combo to zero, play a muted tone, and emit a smaller pink particle burst. When the player passes a gate, award 25 points. If a gate overlaps the player horizontally and the player’s top is below the gate’s height, end the run immediately with a miss; the game has no lives or health system. The player can also simply continue jumping or landing between gates. Keep a scrolling list of gates and remove them once far off-screen. Add small colored square particles for jump/landing effects, with gravity and fading.

HUD/UI should match the visual design. At the top-left, show the uppercase spaced brand “BEATBOUND // RHYTHM RUNNER” in pale periwinkle with a glow. At the top-right, show two dark translucent rounded stat boxes with thin blue borders: SCORE and its numeric value, and COMBO and its value formatted like “0x.” On narrow/mobile screens, show a large rounded gradient button at the bottom center labeled “JUMP ON BEAT”; hide this button on wider desktop screens, where keyboard/canvas input is sufficient. Prevent page scrolling and support safe-area insets.

Before a run, show a centered dark translucent navy rounded card with a thin blue border and shadow. It contains the large white title “Beatbound,” the instruction “Run through the pulse. Tap or press Space exactly on the beat to clear the neon gates.”, a pink-to-purple gradient pill button labeled “START THE TRACK,” and the hint “120 BPM · jump on the glowing pulse.” Starting initializes/resumes Web Audio, resets score/combo/timing/player/gates/particles, hides the card, reveals the mobile jump button, and begins the track.

On collision, stop gameplay and hide the jump button. Show a centered game-over card in the same style with title “Missed the beat,” text in the form “Score [score] · best [best]. Jump when the pulse blooms.”, and a “RUN IT BACK” button that starts a fresh run. Persist the best score in local storage under a Beatbound-specific key and update it at run end. Preserve the score/combo HUD throughout. Include an alternate “Track complete” end title only if the implementation has a natural non-collision completion state, but do not add levels, enemies, collectibles, health, or other mechanics beyond this single endless rhythm run. Make audio start only after a user gesture, keep it unobtrusive, and use Web Audio oscillator/gain envelopes for the simple tones.