Space Invaders Demo Spec

Goal

Build a Space Invaders-style shooter demo that exercises formation movement, enemy waves, projectile collisions, shields, scoring, keyboard input, and clear visual evidence.

The game opens to a cannon at the bottom, a grid of descending enemies, defensive shields, and a HUD. The player moves horizontally, fires upward, avoids enemy shots, protects shields where possible, clears waves, and loses if enemies reach the bottom or lives run out.

Core Rules

Player cannon moves left and right along the bottom.
Player can have only one active shot at a time, or a small fixed limit such as 2 shots.
Enemy formation moves horizontally as a group.
When the formation reaches a side boundary, it steps downward and reverses direction.
Enemies fire downward periodically.
Player shots destroy enemies on contact.
Enemy shots damage shields or the player.
Shields are destructible cell blocks.
The wave is clear when all enemies are destroyed.
The game ends when lives reach zero or enemies reach the player zone.

Controls

Left or A: move player left.
Right or D: move player right.
Space: fire.
P: pause or resume.
R: restart after game over.
Esc: request close when hosted interactively.

Enemies

Use at least 5 columns by 4 rows of enemies.
Enemy rows may have different score values and colors/shapes.
Formation speed increases as fewer enemies remain.
Later waves can add rows, increase fire rate, or increase movement speed.
Optional mystery ship may cross the top occasionally for bonus points.

Scoring

Bottom enemy row: 10 points.
Middle enemy rows: 20 points.
Top enemy row: 40 points.
Mystery ship: 100 points if included.
Wave clear bonus: 300 points times wave number.

Visual Requirements

Render a dark playfield with clear enemy formation, player cannon, projectiles, shields, and HUD.
Use simple pixel-art-like shapes or blocky icons for enemies.
Shields must visibly degrade as they take hits.
Show score, lives, wave, and paused/game-over state.
Projectiles must be visually distinct from enemies and shield blocks.

Game State

Track at minimum:

Player position, lives, cooldown, and active state.
Enemy grid/list with position, row type, alive flag, and formation metadata.
Player projectiles and enemy projectiles.
Shield block grids and health.
Score, wave, formation direction, formation step timer, enemy fire timer, paused flag, game-over flag, elapsed time, and random seed.

Determinism and Evidence

Accept an optional seed for enemy firing and mystery ship timing.
Evidence mode should inject movement and fire input, run enough frames to show formation movement, and complete with a bounded close reason.
Evidence outcome should include frame count, input count, enemies remaining, shield blocks remaining, projectile counts, score, lives, wave, and close reason.
Screenshot evidence should show the player, enemies, shields, at least one projectile or clear HUD state, and the full playfield.

Acceptance Criteria

Player movement is continuous and clamped to the playfield.
Firing creates a projectile subject to the shot limit/cooldown.
Player projectiles destroy enemies and update score.
Enemy formation reverses and descends at side boundaries.
Enemy shots damage shields and player.
Shields degrade visibly.
Clearing all enemies advances the wave.
Enemy reach or zero lives causes game over.
Interactive mode stays open until explicitly closed.

Out of Scope

Exact original arcade timings.
Full sprite animation sheets.
Networked scores.
Required audio.