Multiple fixes for transparency.

- alphaMode is only BLEND for transparent materials.
- We use RawMaterial.type to figure out what's transparent.
- FBX TransparencyFactor is not opacity, but 1.0-opacity.
- Treat vertex coloured materials as transparent
  - We should at least iterate over vertices here and see if any of them
    actually are transparent
- Sort triangles properly: transparent ones render last!

src/Fbx2Raw.cpp

@@ -169,7 +169,7 @@ public:
             fmt::printf("Warning: Mat [%s]: Can't handle texture for %s; discarding.\n", name, FbxSurfaceMaterial::sTransparencyFactor);
         }
         // FBX color is RGB, so we supply the A channel from TransparencyFactor
-        res.colDiffuse[3] = transparency[3];
+        res.colDiffuse[3] = 1.0 - transparency[3];
 
         return res;
     }

src/Raw2Gltf.cpp

@@ -367,6 +367,11 @@ ModelData *Raw2Gltf(
 
         for (int materialIndex = 0; materialIndex < raw.GetMaterialCount(); materialIndex++) {
             const RawMaterial &material = raw.GetMaterial(materialIndex);
+            const bool isTransparent =
+                           material.type == RAW_MATERIAL_TYPE_VERTEX_COLORED ||
+                           material.type == RAW_MATERIAL_TYPE_SKINNED_VERTEX_COLORED ||
+                           material.type == RAW_MATERIAL_TYPE_TRANSPARENT ||
+                           material.type == RAW_MATERIAL_TYPE_SKINNED_TRANSPARENT;
 
             // find a texture by usage and return it as a TextureData*, or nullptr if none exists.
             auto getTex = [&](RawTextureUsage usage)
@@ -407,7 +412,7 @@ ModelData *Raw2Gltf(
             }
             std::shared_ptr<MaterialData> mData = gltf->materials.hold(
                 new MaterialData(
-                    material.name, getTex(RAW_TEXTURE_USAGE_NORMAL),
+                    material.name, isTransparent, getTex(RAW_TEXTURE_USAGE_NORMAL),
                     getTex(RAW_TEXTURE_USAGE_EMISSIVE), material.emissiveFactor,
                     khrComMat, pbrMetRough, pbrSpecGloss));
             materialsByName[materialHash(material)] = mData;

src/RawModel.cpp

@@ -95,7 +95,7 @@ int RawModel::AddTexture(const char *name, const char *fileName, const RawTextur
         }
     }
 
-    const ImageProperties properties = GetImageProperties(name);
+    const ImageProperties properties = GetImageProperties(fileName);
 
     RawTexture texture;
     texture.name      = name;
@@ -421,13 +421,13 @@ void RawModel::CreateMaterialModels(
         // Sort the transparent triangles in the reverse direction.
         std::sort(transparentTriangles.begin(), transparentTriangles.end(), TriangleModelSortNeg::Compare);
 
-        for (const auto &transparentTriangle : transparentTriangles) {
-            sortedTriangles.push_back(transparentTriangle);
-        }
         // Add the triangles to the sorted list.
         for (const auto &opaqueTriangle : opaqueTriangles) {
             sortedTriangles.push_back(opaqueTriangle);
         }
+        for (const auto &transparentTriangle : transparentTriangles) {
+            sortedTriangles.push_back(transparentTriangle);
+        }
     } else {
         sortedTriangles = triangles;
         std::sort(sortedTriangles.begin(), sortedTriangles.end(), TriangleModelSortPos::Compare);

src/glTF/MaterialData.cpp

@@ -153,13 +153,14 @@ void to_json(json &j, const PBRMetallicRoughness &d)
 }
 
 MaterialData::MaterialData(
-    std::string name, const TextureData *normalTexture,
+    std::string name,  bool isTransparent, const TextureData *normalTexture,
     const TextureData *emissiveTexture, const Vec3f & emissiveFactor,
     std::shared_ptr<KHRCommonMats> const khrCommonMats,
     std::shared_ptr<PBRMetallicRoughness> const pbrMetallicRoughness,
     std::shared_ptr<PBRSpecularGlossiness> const pbrSpecularGlossiness)
     : Holdable(),
       name(std::move(name)),
+      isTransparent(isTransparent),
       normalTexture(Tex::ref(normalTexture)),
       emissiveTexture(Tex::ref(emissiveTexture)),
       emissiveFactor(std::move(emissiveFactor)),
@@ -171,7 +172,7 @@ json MaterialData::serialize() const
 {
     json result = {
         { "name", name },
-        { "alphaMode", "BLEND" }
+        { "alphaMode", isTransparent ? "BLEND" : "OPAQUE" }
     };
 
     if (normalTexture != nullptr) {

src/glTF/MaterialData.h

@@ -82,7 +82,7 @@ struct PBRMetallicRoughness
 struct MaterialData : Holdable
 {
     MaterialData(
-        std::string name, const TextureData *normalTexture,
+        std::string name, bool isTransparent, const TextureData *normalTexture,
         const TextureData *emissiveTexture, const Vec3f &emissiveFactor,
         std::shared_ptr<KHRCommonMats> const khrCommonMats,
         std::shared_ptr<PBRMetallicRoughness> const pbrMetallicRoughness,
@@ -91,6 +91,7 @@ struct MaterialData : Holdable
     json serialize() const override;
 
     const std::string                name;
+    const bool                       isTransparent;
     const std::unique_ptr<const Tex> normalTexture;
     const std::unique_ptr<const Tex> emissiveTexture;
     const Vec3f                      emissiveFactor;