PBR Materials

Myth ships with a robust Physically Based Rendering (PBR) material pipeline. PhysicalMaterial supports not only the standard metallic-roughness workflow, but also several advanced surface features from glTF extensions: Clearcoat, Iridescence, Transmission, Sheen, and Anisotropy.

1. The Basic Workflow

PhysicalMaterial uses a chainable builder API. Start from a base color and layer on physical properties:

use myth::prelude::*;

let material = engine.assets.materials.add(
    PhysicalMaterial::new(Vec4::new(0.8, 0.1, 0.1, 1.0)) // base color (RGBA)
        .with_metallic(1.0)      // metallic [0, 1]
        .with_roughness(0.25)    // roughness [0, 1]
);

Intuition for Metallic / Roughness

• Metallic: 0 means dielectric (plastic, wood, skin); 1 means pure metal.
• Roughness: 0 means mirror-smooth; 1 means fully diffuse.

2. Emissive & Texture Maps

let material = PhysicalMaterial::new(Vec4::new(0.1, 0.1, 0.1, 1.0))
    .with_roughness(0.18)
    // Emissive: color + intensity, participates in Bloom
    .with_emissive(Vec3::new(0.25, 0.86, 1.0), 2.2)
    // Albedo map
    .with_map(albedo_tex);

Emissive materials combined with Bloom produce glowing effects like neon signs and energy cores.

3. Advanced Surface Features

The following features correspond to official glTF 2.0 extensions and combine freely with the base properties:

Clearcoat

Adds a transparent coating layer on top of the base material, simulating car paint, varnished wood, etc.:

PhysicalMaterial::new(base_color)
    .with_roughness(0.22)
    .with_clearcoat(1.0, 0.04); // (clearcoat strength, clearcoat roughness)

Sheen

Simulates the soft rim highlight of fabrics like velvet and silk:

PhysicalMaterial::new(base_color)
    .with_roughness(0.92)
    .with_sheen(Vec3::new(0.85, 0.42, 0.96), 0.38); // (sheen color, sheen roughness)

Iridescence

Simulates thin-film interference colors seen in soap bubbles, beetle shells, and oil films:

PhysicalMaterial::new(base_color)
    .with_roughness(0.08)
    .with_iridescence(1.0, 1.3, 120.0, 900.0);
    //               (strength, film IOR, min thickness nm, max thickness nm)

Anisotropy

Simulates directional highlights on brushed metal, hair, etc.:

PhysicalMaterial::new(base_color)
    .with_roughness(0.18)
    .with_anisotropy(0.95, std::f32::consts::PI * 0.35); // (strength, rotation)

Transmission & Dispersion

Implements refractive transparent materials like glass, gems, and liquids:

PhysicalMaterial::new(base_color)
    .with_ior(1.52)          // index of refraction
    .with_roughness(0.03)
    .with_transmission(1.0, 0.55, 4.0, Vec3::new(0.96, 0.98, 1.0));
    //                (transmission, thickness, dispersion, absorption/attenuation color)

Transmission Requires the High-Fidelity Path

Transmissive materials read a refraction background buffer of scene color, depending on the HighFidelity render path and its transmission copy/mipmap stage. See Render Paths & Frame Composer.

4. Other Built-in Materials

Besides PhysicalMaterial, the engine provides lighter-weight material types:

Material	Purpose
PhysicalMaterial	Full PBR, the go-to for production rendering
PhongMaterial	Classic Phong shading, lower cost, good for prototypes / low-end devices
UnlitMaterial	No lighting, outputs color / texture directly, ideal for UI, debugging, skyboxes

// Unaffected by lighting, displays the texture directly
let mat = UnlitMaterial::new(Vec4::ONE).with_map(tex_handle);

Next Steps

• See materials under environment lighting → Procedural Sky & Atmosphere
• Want fully custom materials? → Custom Shaders & Post FX
• Understand the underlying strongly-typed design → Material System