ADD: Support multiple materials per object

assets/buildings/stone_mason/stone_mason.mtl

@@ -9,4 +9,4 @@ Ke 0.000000 0.000000 0.000000
 Ni 1.500000
 d 1.000000
 illum 2
-map_Kd /home/sebastian/Downloads/textures/Image_0.002.webp
+map_Kd stone_mason.png

assets/buildings/stone_mason/stone_masonobj_full.mtl

@@ -0,0 +1,32 @@
+# Blender 5.0.1 MTL File: 'Untitled.blend'
+# www.blender.org
+
+newmtl Cobblestone_tjemdayjw
+Ns 0.000000
+Ka 1.000000 1.000000 1.000000
+Ks 0.000000 0.000000 0.000000
+Ke 0.000000 0.000000 0.000000
+Ni 1.500000
+d 1.000000
+illum 1
+map_Kd textures/tjemdayjw_4K_Albedo_LOD7.jpg
+
+newmtl Cobblestone_tjemdbyiw
+Ns 0.000000
+Ka 1.000000 1.000000 1.000000
+Ks 0.000000 0.000000 0.000000
+Ke 0.000000 0.000000 0.000000
+Ni 1.500000
+d 1.000000
+illum 1
+map_Kd textures/tjemdbyiw_4K_Albedo_LOD6.jpg
+
+newmtl Material_0.002
+Ns 250.000000
+Ka 1.000000 1.000000 1.000000
+Ks 0.500000 0.500000 0.500000
+Ke 0.000000 0.000000 0.000000
+Ni 1.500000
+d 1.000000
+illum 2
+map_Kd textures/stone_mason.png

src/engine/renderer/loader/OBJLoader.cpp

@@ -6,6 +6,8 @@
 
 #define TINYOBJLOADER_IMPLEMENTATION
 #include <complex>
+#include <filesystem>
+#include <iostream>
 
 #include "tiny_obj_loader.h"
 
@@ -14,21 +16,28 @@ std::shared_ptr<TexturedModel> OBJLoader::loadModel(const std::string &modelPath
     std::vector<tinyobj::shape_t> shapes;
     std::vector<tinyobj::material_t> materials;
     std::string warn, err;
-    if (!tinyobj::LoadObj(&attrib, &shapes, &materials, &warn, &err, modelPath.c_str())) {
-        throw std::runtime_error(warn + err);
+    std::string baseDir = std::filesystem::path(modelPath).parent_path().string();
+    bool ret = tinyobj::LoadObj(&attrib, &shapes, &materials, &warn, &err, modelPath.c_str(), baseDir.c_str());
+
+    if (!warn.empty()) {
+        std::cout << "OBJ Loader warning: " << warn << std::endl;
+    }
+    if (!err.empty()) {
+        std::cerr << "OBJ Loader error: " << err << std::endl;
+    }
+    if (!ret) {
+        throw std::runtime_error("Failed to load OBJ");
     }
 
-    if (!tinyobj::LoadObj(&attrib, &shapes, &materials, &warn, &err, modelPath.c_str())) {
-        throw std::runtime_error("Failed to load OBJ: " + warn + err);
-    }
+    std::vector<SubModel> subModels;
 
-    std::vector<float> vertices;
-    std::vector<float> normals;
-    std::vector<float> uvs;
-    std::vector<int> indices;
 
-    int indexOffset = 0;
     for (const auto& shape : shapes) {
+        std::vector<float> vertices;
+        std::vector<float> normals;
+        std::vector<float> uvs;
+        std::vector<int> indices;
+        int indexOffset = 0;
         for (const auto& index : shape.mesh.indices) {
             // Vertex-Position
             vertices.push_back(attrib.vertices[3*index.vertex_index + 0]);
@@ -52,10 +61,30 @@ std::shared_ptr<TexturedModel> OBJLoader::loadModel(const std::string &modelPath
             indices.push_back(indexOffset);
             indexOffset++;
         }
+
+        RawModel rawModel = loader.loadToVAO(vertices, normals, uvs, indices);
+
+        std::shared_ptr<ModelTexture> texture = nullptr;
+        if (!materials.empty() && !shape.mesh.material_ids.empty()) {
+            int matID = shape.mesh.material_ids[0];
+            if (matID >= 0 && matID < static_cast<int>(materials.size())) {
+                tinyobj::material_t &mat = materials[matID];
+                if (!mat.diffuse_texname.empty()) {
+                    std::string texFile = mat.diffuse_texname;
+                    std::filesystem::path fullTexPath = std::filesystem::path(baseDir) / std::filesystem::path(texFile);
+                    texture = std::make_shared<ModelTexture>(loader.loadTextureFromFile(fullTexPath.string()));
+                }
+            }
+        }
+
+        if (!texture) {
+            texture = std::make_shared<ModelTexture>(loader.loadTextureFromFile(texturePath));
+        }
+
+        subModels.emplace_back(
+            std::make_shared<RawModel>(rawModel), texture
+        );
     }
 
-    RawModel rawModel = loader.loadToVAO(vertices, normals, uvs, indices);
-    ModelTexture modelTexture = loader.loadTextureFromFile(texturePath);
-    TexturedModel texturedModel = TexturedModel(std::make_shared<RawModel>(rawModel), std::make_shared<ModelTexture>(modelTexture));
-    return std::make_shared<TexturedModel>(texturedModel);
+    return std::make_shared<TexturedModel>(subModels);
 }

src/game/GameLayer.cpp

@@ -64,6 +64,13 @@ void GameLayer::onAttach()
     EntityID entityID = entityManager->createEntity();
     entityManager->addComponent(entityID, transformComponent);
     entityManager->addComponent(entityID, modelComponent);*/
+
+    auto test = AssetManager::loadModel("test", "assets/buildings/stone_mason/stone_masonobj_full.obj", "assets/buildings/stone_mason/textures/stone_mason.png", loader);
+    auto transformComponent = std::make_shared<TransformComponent>(glm::vec3(0,0,0), glm::vec3(0), 1.f);
+    auto modelComponent = std::make_shared<ModelComponent>(test);
+    EntityID entityID = entityManager->createEntity();
+    entityManager->addComponent(entityID, transformComponent);
+    entityManager->addComponent(entityID, modelComponent);
 }
 
 void GameLayer::onDetach()