前言

目的

如此节标题，为了实现像unity那样保存场景到本地和从本地加载场景的功能
原理

这功能其实就是将场景的实体和组件用文本信息保存起来，加载场景的话就是读取文本信息，根据文本存储的信息，创建实体并且设置组件和组件数据。
用什么存储和解析技术实现

用yaml存储和解析yaml。使用第三方库yaml，将为其写premake文件融入到项目中，使用这个库的存储和解析功能。

地址
为什么不用其它格式存储
- 二进制
  
  虽然有保护性，但是阅读困难对引擎开发人员来说
- Json
  
  Cherno说它的格式{}，会漏掉{}括号，维护有点麻烦。

将yaml项目作为子模块融入项目中

cmd

git submodule add https://github.com/TheCherno/yaml-cpp GameEngineLightWeight/vendor/yaml-cpp

打开yaml-cpp文件夹下的premake.lua，将staticruntime "off"改为
```
staticruntime "on"
```
目的是使yaml-cpp项目作为静态链接

打开项目根目录的premake5.lua,修改的和增加的地方如下：

IncludeDir["yaml_cpp"] = "GameEngineLightWeight/vendor/yaml-cpp/include" -- 用yaml_cpp下划线是因为"%{IncludeDir.yaml_cpp}"只认识_ 不认识-

group "Dependencies"
	include "GameEngineLightWeight/vendor/GLFW"
	include "GameEngineLightWeight/vendor/Glad"
	include "GameEngineLightWeight/vendor/imgui"
	include "GameEngineLightWeight/vendor/yaml-cpp"
group ""

includedirs{
      
      
    "%{prj.name}/src",
    "%{prj.name}/vendor/spdlog/include",
    "%{IncludeDir.Glad}",
    "%{IncludeDir.GLFW}",
    "%{IncludeDir.ImGui}",
    "%{IncludeDir.glm}",
    "%{IncludeDir.stb_image}",
    "%{IncludeDir.entt}",
    "%{IncludeDir.yaml_cpp}"
}
	
links{
      
      
    "GLFW",
    "Glad",
    "ImGui",
    "yaml-cpp",
    "opengl32.lib"
}

重新运行脚本生成新项目

关键的代码

存储

void SceneSerializer::Serialize(const std::string& filepath)
{
      
      
    YAML::Emitter out;
    out << YAML::BeginMap;

    out << YAML::Key << "Scene" << YAML::Value << "Untitled";
    out << YAML::Key << "Entities" << YAML::Value << YAML::BeginSeq;// 开始序列化
    m_Scene->m_Registry.each([&](auto entityID) {
      
      
        Entity entity = {
      
       entityID ,m_Scene.get() };
        if (!entity)
            return;
        // 序列化实体
        SerializeEntity(out, entity);
    });
    out << YAML::EndSeq; // 结束序列化

    out << YAML::EndMap;

    std::ofstream fout(filepath);
    fout << out.c_str();
}
static void SerializeEntity(YAML::Emitter& out, Entity entity) {
      
      
    out << YAML::BeginMap;
    out << YAML::Key << "Entity" << YAML::Value << "12837192831273";
    if (entity.HasComponent<TagComponent>()) {
      
      
        out << YAML::Key << "TagComponent";
        out << YAML::BeginMap;

        auto& tag = entity.GetComponent<TagComponent>().Tag;
        out << YAML::Key << "Tag" << YAML::Value << tag;

        out << YAML::EndMap;
    }
    // 其它组件类似
    out << YAML::EndMap;
}

解析

std::ifstream stream(filepath);
std::stringstream strStream;
strStream << stream.rdbuf(); // strStream流对象中的流重定向到字符串输出流strStream

// 转换为node对象
YAML::Node data = YAML::Load(strStream.str());
if (!data["Scene"]) {
      
      
    return false;
}

std::string sceneName = data["Scene"].as<std::string>();
HZ_CORE_TRACE("Deserializing scene '{0}'", sceneName);

auto entities = data["Entities"];
if (entities) {
      
      
    for (auto entity : entities) {
      
      
        uint64_t uuid = entity["Entity"].as<uint64_t>();

        std::string name;
        auto tagComponent = entity["TagComponent"];
        if (tagComponent) {
      
      
            name = tagComponent["Tag"].as<std::string>();
        }
        HZ_CORE_TRACE("Deserialized entity with ID = {0}, name = {1}", uuid, name);

        Entity deserializedEntity = m_Scene->CreateEntity(name);;

        auto transformComponent = entity["TransformComponent"];
        if (transformComponent) {
      
      
            // 添加实体，默认有transform组件
            auto& tc = deserializedEntity.GetComponent<TransformComponent>();
            tc.Translation = transformComponent["Translation"].as<glm::vec3>();
            tc.Rotation = transformComponent["Rotation"].as<glm::vec3>();
            tc.Scale = transformComponent["Scale"].as<glm::vec3>();
        }
        .....

存储的文件

Scene: Untitled
Entities:
  - Entity: 12837192831273
    TagComponent:
      Tag: Camera B
  - Entity: 12837192831273
    TagComponent:
      Tag: Camera A
  ......

关于yaml的BeginSeq

开了<< YAML::BeginSeq

Scene: Untitled
Entities:
  - Entity: 12837192831273
    TagComponent:
      Tag: Camera B
  - Entity: 12837192831273
    TagComponent:
      Tag: Camera A
  - Entity: 12837192831273
    TagComponent:
      Tag: Green Square Entity
  - Entity: 12837192831273
    TagComponent:
      Tag: Red Square Entity

没开<< YAML::BeginSeq

Scene: Untitled
Entities:
  Entity: 12837192831273
  TagComponent:
    Tag: Camera B
? Entity: 12837192831273
  TagComponent:
    Tag: Camera A
: Entity: 12837192831273
  TagComponent:
    Tag: Green Square Entity
? Entity: 12837192831273
  TagComponent:
    Tag: Red Square Entity

可以看出，BeginSeq是在实体信息前加一个**“-”**，代表着是一个实例

记录bug

问题详情

error LNK2038: 检测到“RuntimeLibrary”的不匹配项: 值“MDd_DynamicDebug”不匹配值“MTd_StaticDebug”(EditorLayer.obj 中)
解决方法

将yaml-cpp项目的运行库改为MTD;

为什么有这个bug

因为在yaml-cpp项目的premake5.lua

filter "system:windows"
    systemversion "latest"
    cppdialect "cpp17"
    staticruntime "off"

staticruntime “off”,代表不是静态链接，所以生成了动态链接dll的选项MDd

要修改成

filter "system:windows"
    systemversion "latest"
    cppdialect "cpp17"
    staticruntime "on"

才是静态链接

Hazel游戏引擎（091）保存和加载场景、序列化场景、Yaml使用

文章目录

前言

将yaml项目作为子模块融入项目中

关键的代码

关于yaml的BeginSeq

记录bug

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