ZX Console Constraints

Comprehensive reference for Nethercore ZX hardware capabilities and constraints. Use this knowledge to validate game concepts, plan memory budgets, and make informed design decisions.

Core Specifications

Memory Budget Planning

ROM Distribution (16 MB Total)

Typical allocation patterns:

Fighting Game (~12 MB):

• Characters (8): ~6 MB (meshes, textures, animations)
• Stages (4): ~3 MB
• Audio (SFX + music): ~2 MB
• Effects, UI, code: ~1 MB

3D Platformer (~10 MB):

• Player + animations: ~500 KB
• Levels (5 worlds × 4 stages): ~5 MB
• Enemies/NPCs: ~2 MB
• Audio: ~2 MB
• Code: ~500 KB

Racing Game (~8 MB):

• Vehicles (12): ~2 MB
• Tracks (6): ~4 MB
• Audio: ~1.5 MB
• Effects, UI, code: ~500 KB

RAM Usage (4 MB Total)

Keep game state small for fast rollback:

• Typical game state: 50-200 KB
• 8-frame rollback at 60fps: ~2ms (well within budget)
• Stack + heap for logic: remaining space

VRAM Budget (4 MB Total)

Active GPU resources:

• Loaded textures
• Mesh vertex/index buffers
• Careful: large textures consume quickly

Render Modes

Choose ONE render mode in init() — cannot change at runtime.

Mode Selection Guidelines

Mode 0 (Lambert) — Side-scrollers, puzzles, retro aesthetics:

• Texture × vertex color (no lighting without normals)
• Simple Lambert shading if normals present
• Lowest GPU cost

Mode 1 (Matcap) — Stylized 3D, character games:

• View-space normal matcap sampling
• Lighting baked into matcap texture
• Good for toon/cartoon aesthetics

Mode 2 (MR-Blinn-Phong) — Modern/realistic:

• Metallic-roughness workflow
• 4 dynamic lights + procedural sun
• Energy-conserving specular

Mode 3 (Blinn-Phong) — Retro 3D, 5th-gen feel:

• Classic specular-shininess
• Rim lighting support
• Era-authentic aesthetic

Audio System

Design implications:

• Lower sample rate = retro sound quality (N64/PS1 era)
• Record/compress as mono, pan in software
• 16 channels is tight for orchestral — plan carefully
• Music via XM tracker format recommended for size

Input System

6th-generation controller layout:

Control scheme guidelines:

• 3D games: prefer analog sticks + triggers
• 2D games: D-pad works well, consider stick as alternative
• Fighting games: all face buttons + D-pad
• Racing: triggers for accelerate/brake, stick for steering

Multiplayer Constraints

• Max 4 players — any mix of local and remote
• GGRS rollback netcode — requires deterministic update()
• Fast rollback — small state enables 8-frame rollback in ~2ms

Determinism requirements:

• All randomness via seeded random() FFI
• Time from tick_count(), not system clock
• No floating-point precision tricks
• State changes ONLY in update(), never in render()

What ZX Excels At

Based on hardware capabilities:

• 3D platformers and action games
• Fighting games (4-player, rollback netcode)
• Racing games (analog triggers, tracks in ROM)
• Third-person adventures
• Split-screen local multiplayer
• Online competitive games

What Requires Careful Planning

• Large open worlds (16 MB ROM limit)
• Orchestral/complex soundtracks (16 channels, 22 kHz)
• Massive texture counts (4 MB VRAM)
• Complex physics simulations (determinism required)

Additional Resources

Reference Files

For detailed constraint breakdowns:

• references/memory-budget-calculator.md — ROM/RAM/VRAM allocation templates
• references/render-mode-comparison.md — Visual examples and use cases

Validation

Before finalizing a game concept, validate:

1. Total asset size fits in 16 MB ROM
2. Game state fits comfortably in RAM for rollback
3. Render mode matches art style goals
4. Audio design fits 16-channel limit
5. Control scheme uses available inputs appropriately