Gem 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.

Recreate a 2D side-scrolling platform runner titled “Gem Runner” using a full-screen responsive HTML canvas with a dark navy overlay UI and bright cartoon graphics. The game should be playable across 50 levels, with a menu shown initially. The core gameplay is an automatically advancing runner: the world scrolls from left to right at a difficulty-dependent speed while the player remains around the left side of the screen (the supplied implementation does not actually apply the left/right key state to player movement, so preserve the simple auto-scroll behavior). The player is a small stylized humanoid with a tan circular head, white eyes, blue rectangular shirt, tan arms, and dark legs. Put the player on a grassy platform at the bottom of the screen; beneath the grass is brown soil with darker round details. The background is a cheerful sky gradient from blue to pale cyan, with soft white clouds and a distant teal rolling landscape/hill layer that moves at a slower parallax rate.

Controls: support Arrow keys or A/D as the advertised movement controls, Space, W, or Up Arrow to jump, and touch buttons at the lower left/lower right for left/right plus an Up button at lower right on mobile. Jumping is the meaningful action: only jump while grounded, apply gravity, and let the player land back on the ground. Difficulty buttons on the menu are Easy, Medium, and Hard. Easy uses speed 270, gravity 1450, jump velocity 620; Medium uses speed 320, gravity 1650, jump velocity 650; Hard uses speed 370, gravity 1800, jump velocity 680.

Generate each level deterministically from its level number. Level length is 5200 plus 115 times the level number in world units. Starting around x=500, repeatedly place obstacles at randomized deterministic gaps of roughly 260–480 units until the level length. Obstacles should include brown/gold-outlined rectangular blockers of varied width and height, dark gray triangular spike groups, and dark moving platforms/blocks with a yellow top stripe that oscillate vertically. Place collectibles around obstacle areas: rotating cyan diamond gems and rotating yellow coin diamonds, usually in short groups of 2–4, at varied airborne heights. The player collects them by proximity; gems increment the gem counter and coins increment the coin counter, with a small toast such as “+1 gem” or “+1 coin” and simple arcade sound effects. Contact with a blocker, spike, or moving obstacle causes a hit, briefly makes the player invulnerable/blinking, decrements the level’s attempts, pauses the game, and opens a modal. Start each level with 3 attempts. The hit modal says “Ouch — blocker hit!” and offers a simulated “Watch ad to resume” button; after a short loading delay it resumes the run from slightly before the checkpoint and grants about 2.5 seconds of protection. It also offers “End game.” If the run ends, show a game-over modal with the reached level and total stars and offer “Retry level” or “Main menu.”

When the runner passes the generated level length, stop gameplay and show a level-complete modal. Award stars based on performance: 3 stars if all three attempts remain and the completion time is below 18 + 1.7 times the level number seconds; otherwise award 2 if at least two attempts remain or the time is below 1.35 times that target, otherwise 1. Display a message such as “Level X complete!”, the earned star icons, and current gem/coin totals. Provide “Next level” (up to level 50) and “Main menu.” Persist mode, current level, gems, coins, stars, and attempts in localStorage so “Resume run” is enabled when a saved run exists.

HUD: place a translucent dark rounded pill at the top left showing a cyan gem icon/count and gold coin icon/count. At the top right show rounded pills for “Level N/50,” star count, and heart/attempt count. Use white bold sans-serif text with subtle shadows. Use a dark translucent modal backdrop with blur, centered rounded navy cards, pale cyan borders, and bright cyan primary buttons; use orange for the rewarded-ad button and red for ending the run. The opening menu card should say “Gem Runner,” explain “Dash through 50 handcrafted-style levels, dodge blockers, and collect gems and coins,” offer the three difficulty buttons, Resume run, New game, and the controls hint. Add subtle synthesized arcade sound effects for jumping, collecting gems/coins, hits, level completion, clicks, and ad resume. Match the visible art direction: clean flat vector-like shapes, saturated cyan/blue sky, vivid green grass, brown soil, navy glassmorphism HUD panels, rounded UI cards, and simple geometric collectibles and hazards.