From 98d8ea9005deb592af039bffad1a6df6b7542e6c Mon Sep 17 00:00:00 2001
From: Michael Oliver <michael.oliver_@outlook.com>
Date: Mon, 27 Apr 2026 13:17:59 +0100
Subject: [PATCH] fix: xmodel glTF dumps dropping `COLOR_0` vertex attributes

---
 src/ObjCommon/XModel/Gltf/JsonGltf.h      |  2 +-
 src/ObjWriting/XModel/Gltf/GltfWriter.cpp | 17 +++++++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/src/ObjCommon/XModel/Gltf/JsonGltf.h b/src/ObjCommon/XModel/Gltf/JsonGltf.h
index fe081504..09a3c7f8 100644
--- a/src/ObjCommon/XModel/Gltf/JsonGltf.h
+++ b/src/ObjCommon/XModel/Gltf/JsonGltf.h
@@ -265,7 +265,7 @@ namespace gltf
         std::optional<unsigned> WEIGHTS_0;
     };
 
-    NLOHMANN_DEFINE_TYPE_EXTENSION(JsonMeshPrimitivesAttributes, POSITION, NORMAL, TEXCOORD_0, JOINTS_0, WEIGHTS_0);
+    NLOHMANN_DEFINE_TYPE_EXTENSION(JsonMeshPrimitivesAttributes, POSITION, NORMAL, COLOR_0, TEXCOORD_0, JOINTS_0, WEIGHTS_0);
 
     class JsonMeshPrimitives
     {
diff --git a/src/ObjWriting/XModel/Gltf/GltfWriter.cpp b/src/ObjWriting/XModel/Gltf/GltfWriter.cpp
index 7dc5a564..0aacfc79 100644
--- a/src/ObjWriting/XModel/Gltf/GltfWriter.cpp
+++ b/src/ObjWriting/XModel/Gltf/GltfWriter.cpp
@@ -23,6 +23,7 @@ namespace
     {
         float coordinates[3];
         float normal[3];
+        float color[4];
         float uv[2];
     };
 
@@ -190,6 +191,7 @@ namespace
 
                 primitives.attributes.POSITION = m_position_accessor;
                 primitives.attributes.NORMAL = m_normal_accessor;
+                primitives.attributes.COLOR_0 = m_color_accessor;
                 primitives.attributes.TEXCOORD_0 = m_uv_accessor;
 
                 if (hasBoneWeightData)
@@ -455,6 +457,15 @@ namespace
             m_normal_accessor = static_cast<unsigned>(gltf.accessors->size());
             gltf.accessors->emplace_back(normalAccessor);
 
+            JsonAccessor colorAccessor;
+            colorAccessor.bufferView = m_vertex_buffer_view;
+            colorAccessor.byteOffset = static_cast<unsigned>(offsetof(GltfVertex, color));
+            colorAccessor.componentType = JsonAccessorComponentType::FLOAT;
+            colorAccessor.count = static_cast<unsigned>(xmodel.m_vertices.size());
+            colorAccessor.type = JsonAccessorType::VEC4;
+            m_color_accessor = static_cast<unsigned>(gltf.accessors->size());
+            gltf.accessors->emplace_back(colorAccessor);
+
             JsonAccessor uvAccessor;
             uvAccessor.bufferView = m_vertex_buffer_view;
             uvAccessor.byteOffset = static_cast<unsigned>(offsetof(GltfVertex, uv));
@@ -545,6 +556,11 @@ namespace
                 vertex->normal[2] = commonVertex.normal[2];
                 LhcToRhcCoordinates(vertex->normal);
 
+                vertex->color[0] = commonVertex.color[0];
+                vertex->color[1] = commonVertex.color[1];
+                vertex->color[2] = commonVertex.color[2];
+                vertex->color[3] = commonVertex.color[3];
+
                 vertex->uv[0] = commonVertex.uv[0];
                 vertex->uv[1] = commonVertex.uv[1];
 
@@ -681,6 +697,7 @@ namespace
         unsigned m_first_bone_node = 0u;
         unsigned m_position_accessor = 0u;
         unsigned m_normal_accessor = 0u;
+        unsigned m_color_accessor = 0u;
         unsigned m_uv_accessor = 0u;
         unsigned m_joints_accessor = 0u;
         unsigned m_weights_accessor = 0u;