Gemini 2.5 Flash × doom

Implement a first-person 3D raycasting engine in a single self-contained HTML file with no external libraries, no external images, and no CDN scripts. This is the hardest challenge in the benchmark. Partial credit is given per requirement met.

## Rendering
- DDA (Digital Differential Analysis) raycasting — not a simplified ray-box approximation
- Fish-eye correction applied to all wall distances
- **Procedurally generated wall textures** using canvas math only (no image files, no data URIs): at least 3 distinct texture patterns (e.g. checkerboard, brick, stripe) assigned to different wall types in the map
- Perspective-correct texture mapping onto wall columns
- Distance-based shading: walls darken smoothly as they recede (multiply shade by 1/distance, clamped)
- Ceiling rendered as a flat dark color; floor as a slightly lighter flat color
- Target: 60fps at 640×480 internal resolution scaled to fill the browser window

## Map
- Hard-coded map of at least 16×16 cells encoded as a 2D array
- Non-trivial layout: at least 3 distinct rooms connected by corridors, one dead end, one secret area
- At least 3 wall types (mapped to the 3 texture patterns)
- One door cell (wall type 4) that opens when the player is within 1.5 cells and presses E; opened doors become passable and render as open archways
- One exit cell — reaching it displays a 'LEVEL COMPLETE — [MM:SS]' overlay
- Player spawn position defined in the map; facing toward the first corridor

## Player
- WASD movement with smooth speed (moveSpeed: 3 cells/sec, rotSpeed: 2 rad/sec)
- Mouse-look for horizontal rotation using the Pointer Lock API (click canvas to lock)
- Collision detection: AABB against all solid walls (player radius: 0.2 cells)
- Field of view: 66 degrees

## Z-buffer
- Maintain a per-column Z-buffer (array of wall distances) for correct depth ordering
- Use it to clip any future sprite/overlay rendering to avoid drawing behind walls

## HUD
- Minimap in top-left corner: draw map cells as colored squares, player as a dot with a direction arrow; scale: 6px per cell
- FPS counter (rolling average over last 30 frames) in top-right corner
- 'Press E to open door' hint rendered in the center-bottom when a door is within 1.5 cells

## Code quality
- Single HTML file, all JS inline in <script> tags, all CSS inline in <style>
- requestAnimationFrame game loop with delta-time movement
- Organized into clearly named functions: initMap(), castRay(), drawWallColumn(), drawHUD(), drawMinimap(), gameLoop(), handleInput()
- No god-object — game state in a plain JS object, renderer functions take state as argument

Scoring: the judge scores each major section (rendering, map, player, HUD, code) independently. A beautiful but mathematically wrong perspective loses on correctness. A correct raycaster with unreadable code loses on quality. Both must be right to score above 8.