fix: material serialization

tests/serialization_tests.cpp

@@ -9,6 +9,7 @@
 #include <destrum/Scene/Scene.h>
 #include <destrum/Scene/SceneManager.h>
 #include <destrum/Serialization/GlmJson.h>
+#include <destrum/Serialization/MaterialSerialization.h>
 #include <destrum/Serialization/SceneSerializer.h>
 #include <destrum/Components/CameraComponent.h>
 #include <destrum/Components/LightComponent.h>
@@ -281,6 +282,58 @@ namespace {
 
         SceneManager::GetInstance().Destroy();
     }
+
+    void testMaterialJsonRoundTrip()
+    {
+        Material material = Material::SimpleColor(glm::vec3{0.2f, 0.4f, 0.6f}, "Crate");
+        material.metallicFactor = 0.3f;
+        material.roughnessFactor = 0.55f;
+        material.emissiveColor = {1.0f, 0.5f, 0.0f};
+        material.textureFilteringMode = TextureFilteringMode::Anisotropic;
+        material.diffuseTexture = 3;
+        material.emissiveTexture = 7;
+        material.normalTexture = 9;
+
+        // Texture 9 has no source file, it must be left out instead of saved as a dangling id
+        const nlohmann::json data = MaterialSerialization::ToJson(material, [](ImageID id) -> nlohmann::json {
+            if (id == 9) {
+                return nullptr;
+            }
+            return {{"path", "game://tex" + std::to_string(id) + ".png"}, {"srgb", id == 3}};
+        });
+        check(!MaterialSerialization::Validate(nlohmann::json{{"Crate", data}}).has_value(),
+              "a serialized material must pass validation");
+        check(!data.at("textures").contains("normal"), "textures without a source must not be saved");
+
+        const Material loaded = MaterialSerialization::FromJson(data, [](const nlohmann::json& texture) {
+            const std::string path = texture.at("path").get<std::string>();
+            return path == "game://tex3.png" ? ImageID{30} : ImageID{70};
+        });
+        check(loaded.name == "Crate" && loaded.baseColor == material.baseColor &&
+              close(loaded.metallicFactor, 0.3f) && close(loaded.roughnessFactor, 0.55f) &&
+              loaded.emissiveColor == material.emissiveColor &&
+              loaded.textureFilteringMode == TextureFilteringMode::Anisotropic,
+              "material factors must round-trip through json");
+        check(loaded.diffuseTexture == 30 && loaded.emissiveTexture == 70 &&
+              loaded.normalTexture == NULL_IMAGE_ID && loaded.metallicTexture == NULL_IMAGE_ID,
+              "material textures must round-trip through their slots");
+    }
+
+    void testSceneValidatesEmbeddedMaterials()
+    {
+        const auto path = std::filesystem::temp_directory_path() / "destrum_materials_scene.json";
+        Scene& scene = SceneManager::GetInstance().CreateScene("materials");
+
+        std::ofstream{path} << R"({"version":2,"objects":[],"materials":{"Bad":{"textures":{"diffuse":5}}}})";
+        check(!SceneSerializer::Load(scene, path), "a material texture without a path must be rejected");
+
+        std::ofstream{path} << R"({"version":2,"objects":[{"id":1,"name":"box"}],)"
+                              R"("materials":{"Good":{"baseColor":[1,0,0],"textures":{"diffuse":{"path":"game://a.png"}}}}})";
+        check(SceneSerializer::Load(scene, path), "a scene with embedded materials must load");
+        std::filesystem::remove(path);
+
+        SceneManager::GetInstance().Destroy();
+    }
 }
 
 void RunSerializationTests()
@@ -295,4 +348,6 @@ void RunSerializationTests()
     testSceneLoadDropsMissingCamera();
     testGlmJson();
     testSceneFileIdsAreLocal();
+    testMaterialJsonRoundTrip();
+    testSceneValidatesEmbeddedMaterials();
 }