Beatbound Runner

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 2D rhythm endless runner titled “Beatbound Runner,” rendered on a full-screen HTML canvas with a fixed logical playfield of 1200×700 that scales responsively to the viewport while preserving aspect ratio and centers letterboxed content. Use a dark neon aesthetic: a vertical navy gradient background (#0c1130 to #080b18), approximately 70 subtly twinkling pale stars in the upper sky, and a faint cyan perspective grid converging toward the center around y=390. Along the bottom gameplay lane at y=530, draw a thin glowing cyan horizontal track line.

The player is an always-forward-running, stationary-in-horizontal-position cyan rounded rectangle character at x=190, about 34×52 pixels, with a soft cyan glow, two dark circular eyes, and a simple dark smiling arc. The character automatically runs; there is no horizontal movement control. It jumps vertically using gravity: launch velocity about -720, gravity about 1900, and land back on the lane. Add a slight squash/stretch effect and emit small cyan and pink square particles when jumping.

The core mechanic is timing jumps to a 120 BPM rhythm. One beat is 0.5 seconds. On every beat, play simple synthesized Web Audio percussion/tones: an alternating low bass pulse, a higher triangle tone, rapid high ticks subdividing the beat, and an occasional sawtooth accent. Display a centered beat indicator near the top: a 76px cyan outlined ring that briefly expands and turns pink on each beat, with a label that alternates between “JUMP ON THE PULSE” during the first half of a beat and “KEEP RUNNING” during the second half. Obstacles begin after the first few beats and spawn on every second beat starting at beat index 4 (the code condition is beat index >2 and even). Each obstacle enters from the right at x=1240 and moves left across the lane. It is a glowing pink rounded rectangle roughly 34×42 pixels, positioned with its bottom near the lane, with two small pale vertical highlights inside and a subtle bobbing motion. Movement speed starts around 360 pixels/second and increases gradually by 4 pixels/second per elapsed second, capped at an additional 240.

When the player presses jump, determine the nearest beat and compare the press timing to it. If within 0.055 seconds, award “PERFECT,” increase combo, and add 100 plus 10×the new combo to score. If within 0.14 seconds but not perfect, award “ON BEAT,” increase combo, and add 50 plus 5×the new combo. Otherwise reset combo to zero and show “OFF BEAT.” Show feedback text centered high on the screen in the matching cyan, pale cyan, or pink color, glowing and fading after about half a second. Jump is allowed only while grounded, so a jump attempt in midair does nothing. Passing an obstacle awards 20 points. If the player overlaps an obstacle while sufficiently near the lane, end the run immediately with the reason/title “Catch the downbeat.” Store and update a persistent best score in localStorage under the key “beatbound-best.”

Build a fixed HUD over the canvas. At top left show the uppercase spaced cyan brand “BEATBOUND RUNNER.” At top right show three translucent dark rounded stat pills with small uppercase labels and bold values: SCORE, COMBO (shown like “0x”), and BEST. At the bottom left show the hint “Jump on the pulse — Space, W, or tap JUMP. Land on rhythm to build your combo.” Hide this hint on narrow mobile screens. At bottom right show a large pink gradient rounded “JUMP” button, usable by pointer/touch and sized responsively.

On initial load, pause gameplay and show a centered modal overlay with a dark radial backdrop. The rounded dark translucent card has a pink uppercase eyebrow “A RHYTHM RUNNER,” a large two-line title “Run the” and cyan “beat.”, explanatory text “Obstacles arrive on the downbeat. Jump with the music and keep the combo alive.”, and a bright cyan rounded button labeled “START THE TRACK.” Starting initializes/resumes audio, resets score, combo, player, obstacles, particles, and beat timing, then hides the overlay. Support keyboard Space, W, or Up Arrow for jump; if the game has not started, these keys start it. The touch button also triggers jump and initializes audio.

On collision, stop the run and show the overlay again with a second card replacing the start card: pink eyebrow “TRACK ENDED,” a large title using the collision reason “Catch the downbeat,” a result line such as “Score 0 · Best 0,” and a bright button “RUN IT BACK.” Restart fully resets the run but retains the persistent best score. Include responsive pointer/touch behavior, prevent page scrolling, and use neon cyan/pink glow, translucent panels, rounded corners, uppercase letter spacing, and smooth feedback transitions to match the provided visual style.