Derive macros for the RDPE particle simulation engine.

This crate provides three derive macros:

• [Particle] - Generates GPU-compatible structs and WGSL code
• [ParticleType] - Creates type-safe enums for particle categories
• [MultiParticle] - Combines multiple Particle types into one simulation

Usage

These macros are re-exported from the main rdpe crate. You don't need to add this crate directly:

use rdpe::prelude::*;

#[derive(Particle, Clone)]
struct Ball {
    position: Vec3,
    velocity: Vec3,
}

#[derive(ParticleType, Clone, Copy, PartialEq)]
enum Species {
    Prey,
    Predator,
}

The Particle Macro

#[derive(Particle)] transforms your Rust struct into a GPU-compatible format. It generates:

• A companion {Name}Gpu struct with proper alignment and padding
• A WGSL_STRUCT constant containing the WGSL struct definition
• to_gpu() method for converting Rust → GPU format

Required Fields

Every particle must have:

• position: Vec3 - Particle position in 3D space
• velocity: Vec3 - Particle velocity

Optional Fields

• particle_type: u32 - For typed interactions (auto-added if missing)
• #[color] color: Vec3 - Custom particle color
• Any f32, u32, i32, Vec2, Vec3, Vec4 fields

GPU Memory Layout

The macro handles WGSL's strict alignment requirements:

• Vec3 requires 16-byte alignment (even though it's only 12 bytes)
• Struct total size must be a multiple of 16 bytes
• Padding fields are automatically inserted

The ParticleType Macro

#[derive(ParticleType)] enables type-safe particle categories for use with typed rules like Chase, Evade, and Convert.

It generates:

• From<EnumName> for u32 - Convert enum to GPU-compatible integer
• From<u32> for EnumName - Convert back (defaults to first variant)
• EnumName::count() -> u32 - Number of variants