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

Spec	Value	Design Implication
Resolution	960×540 fixed	UI safe zones required, 16:9 aspect
Color depth	32-bit RGBA8	Full color, no palette limitations
ROM	16 MB	WASM + all assets must fit
RAM	4 MB	Game state only (fast rollback)
VRAM	4 MB	GPU textures and mesh buffers
Tick rate	24/30/60/120 fps	Choose based on game needs
Max players	4	Local + remote mix supported
Alpha	2-bit Bayer 4×4	16 threshold levels for transparency

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	Name	Best For	Cost
0	Lambert	2D games, UI, sprites, flat stylized	Lowest
1	Matcap	Stylized 3D, toon shading, metallic	Low
2	MR-Blinn-Phong	PBR materials, realistic surfaces	Medium
3	Blinn-Phong	5th-gen retro, artistic specular	Medium

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

Spec	Value
Sample rate	22,050 Hz
Format	16-bit signed PCM, mono
Sound channels	16 simultaneous
Music channel	1 dedicated (looping)
Panning	Equal-power stereo (-1.0 to +1.0)

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:

Input	Type	Notes
D-Pad	4-way digital	Best for 2D precision
Face buttons	A, B, X, Y	Standard action buttons
Bumpers	L1, R1	Digital shoulder buttons
Triggers	L2, R2	Analog (0.0-1.0)
Sticks	Left + Right	Analog (-1.0 to 1.0) with L3/R3 click
Menu	Start, Select	Standard menu buttons

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