Derive Macro Particle 

#[derive(Particle)]
{
    // Attributes available to this derive:
    #[color]
}

Derive macro for particle structs.

Transforms a Rust struct into a GPU-compatible particle type. Generates:

• A companion {Name}Gpu struct with #[repr(C)] and proper WGSL alignment
• Implementation of ParticleTrait
• WGSL struct definition as a const string

Required Fields

Every particle must have these fields:

Field	Type	Purpose
position	Vec3	Particle location in 3D space
velocity	Vec3	Particle movement direction and speed

Optional Fields

Field	Type	Purpose
particle_type	u32	Category for typed interactions (auto-added if missing)
#[color] name	Vec3	Custom particle color (RGB, 0.0-1.0)
(any name)	f32, u32, i32, Vec2, Vec3, Vec4	Custom data

Supported Types

Rust Type	WGSL Type	Size	Alignment
Vec3	vec3<f32>	12 bytes	16 bytes
Vec2	vec2<f32>	8 bytes	8 bytes
Vec4	vec4<f32>	16 bytes	16 bytes
f32	f32	4 bytes	4 bytes
u32	u32	4 bytes	4 bytes
i32	i32	4 bytes	4 bytes

GPU Memory Layout

WGSL has strict alignment requirements that differ from Rust. This macro automatically inserts padding fields to ensure correct GPU memory layout:

• Vec3 requires 16-byte alignment (despite being 12 bytes)
• Arrays of structs require 16-byte stride
• Padding fields are named _pad0, _pad1, etc.

The #[color] Attribute

Mark a Vec3 field with #[color] to use it for particle rendering:

#[derive(Particle, Clone)]
struct Firework {
    position: Vec3,
    velocity: Vec3,
    #[color]
    color: Vec3,  // RGB values 0.0-1.0
}

Without #[color], particles are colored based on their position.

Example

use rdpe::prelude::*;

// Minimal particle
#[derive(Particle, Clone)]
struct Basic {
    position: Vec3,
    velocity: Vec3,
}

// Full-featured particle
#[derive(Particle, Clone)]
struct Advanced {
    position: Vec3,
    velocity: Vec3,
    #[color]
    color: Vec3,
    particle_type: u32,
    energy: f32,
    age: f32,
}

Generated Code

For a particle Ball, the macro generates:

// GPU-compatible struct
#[repr(C)]
#[derive(Clone, Copy, bytemuck::Pod, bytemuck::Zeroable)]
pub struct BallGpu {
    pub position: [f32; 3],
    pub _pad0: f32,  // Alignment padding
    pub velocity: [f32; 3],
    pub _pad1: f32,
    pub particle_type: u32,
    pub _pad2: [f32; 3],  // Struct size padding
}

impl ParticleTrait for Ball {
    type Gpu = BallGpu;
    const WGSL_STRUCT: &'static str = "...";
    // ...
}

Panics

The macro panics at compile time if:

• Applied to an enum instead of a struct
• Struct uses tuple fields instead of named fields
• Any field has an unsupported type