material_asset.h

#pragma once
 
#include <cstddef>
#include <cstdint>
 
#include <glm/glm.hpp>
 
#include "resource/resource.h"
#include "resource/resource_handle.h"
 
#include "resource/asset/texture_asset.h"
 
#include "core/reflect.h"
 
namespace Vkm::Engine {

#define VKM_MATERIAL_MAPS(X)                                                                                                            \
    X(albedo,              albedoTexture,              ALBEDO,                Base color (RGBA; A feeds AlphaMask / Transparent))       \
    X(normal,              normalTexture,              NORMAL,                Tangent-space normal map (RGB))                           \
    X(metallicRoughness,   metallicRoughnessTexture,   METALLIC_ROUGHNESS,    Combined roughness (G) + metallic (B) in the glTF layout) \
    X(metallic,            metallicTexture,            METALLIC,              Separate metalness (R channel))                           \
    X(roughness,           roughnessTexture,           ROUGHNESS,             Separate roughness (R channel))                           \
    X(ao,                  aoTexture,                  AO,                    Ambient occlusion (R channel))                            \
    X(aoMetallicRoughness, aoMetallicRoughnessTexture, AO_METALLIC_ROUGHNESS, Combined AO (R) + roughness (G) + metallic (B))           \
    X(emission,            emissionTexture,            EMISSION,              Emission (RGB))                                           \
    X(height,              heightTexture,              HEIGHT,                Height field for parallax (R channel, white is high))     \
    X(clearcoat,           clearcoatTexture,           CLEARCOAT,             Clearcoat strength mask (R channel))                      \
    X(transmission,        transmissionTexture,        TRANSMISSION,          Transmission mask (R channel))

#define VKM_MATERIAL_MAP_COUNT(key, member, slot, doc) +1
inline constexpr std::size_t MATERIAL_MAP_COUNT = 0 VKM_MATERIAL_MAPS(VKM_MATERIAL_MAP_COUNT);
#undef VKM_MATERIAL_MAP_COUNT

enum class MaterialType : uint8_t {
    Opaque      = 0,
    Transparent = 1,
    Unlit       = 2,
    AlphaMask   = 3,
    Count
};

struct MaterialAsset : public Resource {
    MaterialType type = MaterialType::Opaque;
    float alphaCutoff = 0.5f;

    glm::vec4 albedo   = {1,1,1,1};
    float metallic     = 0.0f;                   
    float roughness    = 0.5f;
    float ior          = 1.5f;                   
    float ao           = 1.0f;
    float normalScale  = 1.0f;
 
    glm::vec3 emission     = {0,0,0};            
    float emissiveStrength = 1.0f;               

    float clearcoat               = 0.0f;
    float clearcoatRoughness      = 0.0f;        
    float anisotropy              = 0.0f;        
    glm::vec3 anisotropyDirection = {1,0,0};     
 
    glm::vec3 sheenColor     = {0,0,0};          
    float     sheenRoughness = 0.3f;             
 
    float subsurface          = 0.0f;            
    glm::vec3 subsurfaceColor = {1,1,1};         

    float transmission = 0.0f;
    // KHR_materials_volume: transmittance = pow(attenuationColor, path / attenuationDistance),
    // the path from thicknessFactor.
    float     thicknessFactor     = 0.0f;
    float     attenuationDistance = 1.0f;
    glm::vec3 attenuationColor    = {1,1,1};

    float heightScale = 0.0f;
 
#define VKM_MATERIAL_MAP_MEMBER(key, member, slot, doc) TextureHandle member;
    VKM_MATERIAL_MAPS(VKM_MATERIAL_MAP_MEMBER)
#undef VKM_MATERIAL_MAP_MEMBER
};
 
using MaterialHandle = Handle<MaterialAsset>;
 
} // namespace Vkm::Engine
 
VKM_ENUM_NAMES(::Vkm::Engine::MaterialType, "Opaque", "Transparent", "Unlit", "AlphaMask")
 
// Non-texture fields; texture handles serialize separately as name refs.
VKM_REFLECT_BEGIN(::Vkm::Engine::MaterialAsset)
    VKM_F(type)
    VKM_F(alphaCutoff)
    VKM_F(albedo)
    VKM_F(metallic)
    VKM_F(roughness)
    VKM_F(ior)
    VKM_F(ao)
    VKM_F(normalScale)
    VKM_F(emission)
    VKM_F(emissiveStrength)
    VKM_F(clearcoat)
    VKM_F(clearcoatRoughness)
    VKM_F(anisotropy)
    VKM_F(anisotropyDirection)
    VKM_F(sheenColor)
    VKM_F(sheenRoughness)
    VKM_F(subsurface)
    VKM_F(subsurfaceColor)
    VKM_F(transmission)
    VKM_F(thicknessFactor)
    VKM_F(attenuationDistance)
    VKM_F(attenuationColor)
    VKM_F(heightScale)
VKM_REFLECT_END()