Added gltf2 KHR_materials_volume import support.

code/AssetLib/glTF2/glTF2Asset.h

@@ -49,6 +49,7 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *   KHR_materials_sheen full
  *   KHR_materials_clearcoat full
  *   KHR_materials_transmission full
+ *   KHR_materials_volume full
  */
 #ifndef GLTF2ASSET_H_INC
 #define GLTF2ASSET_H_INC
@@ -713,6 +714,7 @@ const vec3 defaultEmissiveFactor = { 0, 0, 0 };
 const vec4 defaultDiffuseFactor = { 1, 1, 1, 1 };
 const vec3 defaultSpecularFactor = { 1, 1, 1 };
 const vec3 defaultSheenFactor = { 0, 0, 0 };
+const vec3 defaultAttenuationColor = { 1, 1, 1 };
 
 struct TextureInfo {
     Ref<Texture> texture;
@@ -777,6 +779,16 @@ struct MaterialTransmission {
     float transmissionFactor = 0.f;
 };
 
+struct MaterialVolume {
+    float thicknessFactor = 0.f;
+    TextureInfo thicknessTexture;
+    float attenuationDistance = 0.f;
+    vec3 attenuationColor;
+
+    MaterialVolume() { SetDefaults(); }
+    void SetDefaults();
+};
+
 //! The material appearance of a primitive.
 struct Material : public Object {
     //PBR metallic roughness properties
@@ -803,6 +815,9 @@ struct Material : public Object {
     //extension: KHR_materials_transmission
     Nullable<MaterialTransmission> materialTransmission;
 
+    //extension: KHR_materials_volume
+    Nullable<MaterialVolume> materialVolume;
+    
     //extension: KHR_materials_unlit
     bool unlit;
 
@@ -1091,6 +1106,7 @@ public:
         bool KHR_materials_sheen;
         bool KHR_materials_clearcoat;
         bool KHR_materials_transmission;
+        bool KHR_materials_volume;
         bool KHR_draco_mesh_compression;
         bool FB_ngon_encoding;
         bool KHR_texture_basisu;

code/AssetLib/glTF2/glTF2Asset.inl

@@ -1215,6 +1215,19 @@ inline void Material::Read(Value &material, Asset &r) {
             }
         }
 
+        if (r.extensionsUsed.KHR_materials_volume) {
+            if (Value *curMaterialVolume = FindObject(*extensions, "KHR_materials_volume")) {
+                MaterialVolume volume;
+
+                ReadMember(*curMaterialVolume, "thicknessFactor", volume.thicknessFactor);
+                ReadTextureProperty(r, *curMaterialVolume, "thicknessTexture", volume.thicknessTexture);
+                ReadMember(*curMaterialVolume, "attenuationDistance", volume.attenuationDistance);
+                ReadMember(*curMaterialVolume, "attenuationColor", volume.attenuationColor);
+
+                this->materialVolume = Nullable<MaterialVolume>(volume);
+            }
+        }
+
         unlit = nullptr != FindObject(*extensions, "KHR_materials_unlit");
     }
 }
@@ -1260,6 +1273,13 @@ inline void MaterialSheen::SetDefaults() {
     sheenRoughnessFactor = 0.f;
 }
 
+inline void MaterialVolume::SetDefaults() {
+    //KHR_materials_volume properties
+    thicknessFactor = 0.f;
+    attenuationDistance = INFINITY;
+    SetVector(attenuationColor, defaultAttenuationColor);
+}
+
 namespace {
 
 template <int N>
@@ -1931,6 +1951,7 @@ inline void Asset::ReadExtensionsUsed(Document &doc) {
     CHECK_EXT(KHR_materials_sheen);
     CHECK_EXT(KHR_materials_clearcoat);
     CHECK_EXT(KHR_materials_transmission);
+    CHECK_EXT(KHR_materials_volume);
     CHECK_EXT(KHR_draco_mesh_compression);
     CHECK_EXT(KHR_texture_basisu);
 

code/AssetLib/glTF2/glTF2Importer.cpp

@@ -341,6 +341,16 @@ static aiMaterial *ImportMaterial(std::vector<int> &embeddedTexIdxs, Asset &r, M
             SetMaterialTextureProperty(embeddedTexIdxs, r, transmission.transmissionTexture, aimat, AI_MATKEY_TRANSMISSION_TEXTURE);
         }
 
+        // KHR_materials_volume
+        if (mat.materialVolume.isPresent) {
+            MaterialVolume &volume = mat.materialVolume.value;
+
+            aimat->AddProperty(&volume.thicknessFactor, 1, AI_MATKEY_VOLUME_THICKNESS_FACTOR);
+            SetMaterialTextureProperty(embeddedTexIdxs, r, volume.thicknessTexture, aimat, AI_MATKEY_VOLUME_THICKNESS_TEXTURE);
+            aimat->AddProperty(&volume.attenuationDistance, 1, AI_MATKEY_VOLUME_ATTENUATION_DISTANCE);
+            SetMaterialColorProperty(r, volume.attenuationColor, aimat, AI_MATKEY_VOLUME_ATTENUATION_COLOR);
+        }
+
         return aimat;
     } catch (...) {
         delete aimat;

include/assimp/material.h

@@ -318,6 +318,12 @@ enum aiTextureType {
     */
     aiTextureType_TRANSMISSION = 21,
 
+    /** Volume
+    * Simulates transmission through the surface
+    * May include further information such as wall thickness
+    */
+    aiTextureType_VOLUME = 22,
+
     /** Unknown texture
      *
      *  A texture reference that does not match any of the definitions
@@ -1028,6 +1034,17 @@ extern "C" {
 // Multiplied by AI_MATKEY_TRANSMISSION_FACTOR
 #define AI_MATKEY_TRANSMISSION_TEXTURE aiTextureType_TRANSMISSION, 0
 
+// Volume
+// ------------
+// https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_materials_volume
+// Base percentage of light transmitted through the surface. 0.0 = Opaque, 1.0 = Fully transparent
+#define AI_MATKEY_VOLUME_THICKNESS_FACTOR "$mat.volume.thicknessFactor", 0, 0
+// Texture defining percentage of light transmitted through the surface.
+// Multiplied by AI_MATKEY_THICKNESS_FACTOR
+#define AI_MATKEY_VOLUME_THICKNESS_TEXTURE aiTextureType_VOLUME, 0
+#define AI_MATKEY_VOLUME_ATTENUATION_DISTANCE "$mat.volume.attenuationDistance", 0, 0
+#define AI_MATKEY_VOLUME_ATTENUATION_COLOR "$mat.volume.attenuationColor", 0, 0
+
 // Emissive
 // --------
 #define AI_MATKEY_USE_EMISSIVE_MAP "$mat.useEmissiveMap", 0, 0