Vulkan教程 – 03 验证层-卡核

Vulkan API设计一开始就是要减轻驱动负担，所以API本身的错误检查很少。但是并不表示我们不能向API添加这些检查，这也就是validation layers的功能了。验证层中常用的操作有：

检查参数值以避免误用；

追踪创建和销毁对象以查找资源泄露；

检查线程安全；

记录每次调用的参数；

跟踪Vulkan调用以进行分析和重现。

验证层必须要安装到系统中之后才能使用，比如LunarG验证层就只能在电脑上安装了VulkanSDK后才能用。

下面看如何启用标准的诊断层，这和扩展一样，需要通过指定它们的名称来开启。这些很有用的标准验证都绑定到了SDK的VK_LAYER_KHRONOS_validation层中。先添加两个配置变量，根据是否是debug模式来确定是否启用，这里用了一个NDEBUG宏：

#ifdef NDEBUG
const bool enableValidationLayers = false;
#else
const bool enableValidationLayers = true;
#endif

下面添加一个方法检查是否所有所需的层都可用，首先列出所有可用的层：

bool checkValidationLayerSupport() {
    uint32_t layerCount;
    vkEnumerateInstanceLayerProperties(&layerCount, nullptr);

    std::vector<VkLayerProperties> availableLayers(layerCount);
    vkEnumerateInstanceLayerProperties(&layerCount, availableLayers.data());

    return false;
}

接着检查validationLayers所有的层是否都在availableLayers中：

bool checkValidationLayerSupport() {
    uint32_t layerCount;
    vkEnumerateInstanceLayerProperties(&layerCount, nullptr);

    std::vector<VkLayerProperties> availableLayers(layerCount);
    vkEnumerateInstanceLayerProperties(&layerCount, availableLayers.data());

    for (const char* layerName : validationLayers) {
        bool layerFound = false;

        for (const auto& layerProperties : availableLayers) {
            if (strcmp(layerName, layerProperties.layerName) == 0) {
                layerFound = true;
                break;
            }
        }

        if (!layerFound) {
            return false;
        }
    }

    return true;
}

现在就能在createInstance方法中调用了：

void createInstance() {
    if (enableValidationLayers && !checkValidationLayerSupport()) {
        throw std::runtime_error("validation layers requested, but not available!");
    }

    ...
}

接着将原来的：

createInfo.enabledLayerCount = 0;

修改为：

if (enableValidationLayers) {
    createInfo.enabledLayerCount = static_cast<uint32_t>(validationLayers.size());
    createInfo.ppEnabledLayerNames = validationLayers.data();
} else {
    createInfo.enabledLayerCount = 0;
}

不幸的是，只启用这些层并没有太多帮助，因为当前还不能将这些调试信息返回给我们的程序。为了接收这些信息，我们需要搭建一个调试信息回调，需要VK_EXT_debug_utils扩展。先创建函数getRequiredExtensions，获取扩展列表：

std::vector<const char*> getRequiredExtensions() {
    uint32_t glfwExtensionCount = 0;
    const char** glfwExtensions;
    glfwExtensions = glfwGetRequiredInstanceExtensions(&glfwExtensionCount);
    std::vector<const char*> extensions(glfwExtensions, glfwExtensions + glfwExtensionCount);

    if (enableValidationLayers) {
        extensions.push_back(VK_EXT_DEBUG_UTILS_EXTENSION_NAME);
    }

    return extensions;
}

调试回调函数如下：

static VKAPI_ATTR VkBool32 VKAPI_CALL debugCallback(
    VkDebugUtilsMessageSeverityFlagBitsEXT messageSeverity,
    VkDebugUtilsMessageTypeFlagsEXT messageType,
    const VkDebugUtilsMessengerCallbackDataEXT* pCallbackData,
    void* pUserData) {
    std::cerr << "validation layer: " << pCallbackData->pMessage << std::endl;

    return VK_FALSE;
}

第一个参数表明信息严重性等级，第二个是消息类型，第三个参数是回调数据参数，会包含pMessage、pObjects和objectCount等信息。现在要告诉Vulkan回调函数了，在类中添加一个成员：

VkDebugUtilsMessengerEXT debugMessenger;

现在添加函数以便initVulkan中创建实例后调用：

void initVulkan() {
    createInstance();
    setupDebugMessenger();
}

void setupDebugMessenger() {
    if (!enableValidationLayers) return;

}

我们应该设置结构体，以添加消息处理器和回调的详情：

VkDebugUtilsMessengerCreateInfoEXT createInfo = {};
createInfo.sType = VK_STRUCTURE_TYPE_DEBUG_UTILS_MESSENGER_CREATE_INFO_EXT;
createInfo.messageSeverity = VK_DEBUG_UTILS_MESSAGE_SEVERITY_VERBOSE_BIT_EXT |
    VK_DEBUG_UTILS_MESSAGE_SEVERITY_WARNING_BIT_EXT;
createInfo.messageType = VK_DEBUG_UTILS_MESSAGE_TYPE_GENERAL_BIT_EXT |
    VK_DEBUG_UTILS_MESSAGE_TYPE_VALIDATION_BIT_EXT |
    VK_DEBUG_UTILS_MESSAGE_TYPE_PERFORMANCE_BIT_EXT;
createInfo.pfnUserCallback = debugCallback;
createInfo.pUserData = nullptr;

messageSeverity可以设置什么时候调用回调函数，这里除了info级别的全都写了。这个结构体应该传给vkCreateDebugUtilsMessengerEXT方法，以创建VkDebugUtilsMessengerEXT对象。可是这个方法却是个扩展方法，不会自动加载。我们需要查看它的地址，用vkGetInstanceProcAddr方法即可获得。我们要创建自己的代理函数来在后台自动处理这个任务，就放在HelloTriangleApplication类之前：

VkResult CreateDebugUtilsMessengerEXT(
    VkInstance instance,
    const VkDebugUtilsMessengerCreateInfoEXT* pCreateInfo,
    const VkAllocationCallbacks* pAllocator,
    VkDebugUtilsMessengerEXT* pDebugMessenger) {
    auto func = (PFN_vkCreateDebugUtilsMessengerEXT)vkGetInstanceProcAddr(instance, "vkCreateDebugUtilsMessengerEXT");
    if (func != nullptr) {
        return func(instance, pCreateInfo, pAllocator, pDebugMessenger);
    } else {
        return VK_ERROR_EXTENSION_NOT_PRESENT;
    }
}

如果方法不能成功加载，vkGetInstanceProcAddr方法就会返回nullptr。如果有的话我们就能调用该方法创建扩展对象了：

if (CreateDebugUtilsMessengerEXT(instance, &createInfo, nullptr, &debugMessenger) != VK_SUCCESS) {
    throw std::runtime_error("failed to set up debug messenger!");
}

对应的，还需要一个销毁函数：

void DestroyDebugUtilsMessengerEXT(
    VkInstance instance,
    VkDebugUtilsMessengerEXT debugMessenger,
    const VkAllocationCallbacks* pAllocator) {
    auto func = (PFN_vkDestroyDebugUtilsMessengerEXT)vkGetInstanceProcAddr(instance, "vkDestroyDebugUtilsMessengerEXT");
    if (func != nullptr) {
        func(instance, debugMessenger, pAllocator);
    }
}

这样就能在cleanup中调用了：

void cleanup() {
    if (enableValidationLayers) {
        DestroyDebugUtilsMessengerEXT(instance, debugMessenger, nullptr);
    }
    vkDestroyInstance(instance, nullptr);
    glfwDestroyWindow(window);
    glfwTerminate();
}

最终完整代码如下：

#define GLFW_INCLUDE_VULKAN
#include <GLFW/glfw3.h>

#include <iostream>
#include <stdexcept>
#include <functional>
#include <cstdlib>

const int WIDTH = 800;
const int HEIGHT = 600;
const std::vector<const char*> validationLayers = {
    "VK_LAYER_KHRONOS_validation"
};

#ifdef NDEBUG
const bool enableValidationLayers = false;
#else
const bool enableValidationLayers = true;
#endif

VkResult CreateDebugUtilsMessengerEXT(
    VkInstance instance,
    const VkDebugUtilsMessengerCreateInfoEXT* pCreateInfo,
    const VkAllocationCallbacks* pAllocator,
    VkDebugUtilsMessengerEXT* pDebugMessenger) {
    auto func = (PFN_vkCreateDebugUtilsMessengerEXT)vkGetInstanceProcAddr(instance, "vkCreateDebugUtilsMessengerEXT");
    if (func != nullptr) {
        return func(instance, pCreateInfo, pAllocator, pDebugMessenger);
    } else {
        return VK_ERROR_EXTENSION_NOT_PRESENT;
    }
}

void DestroyDebugUtilsMessengerEXT(
    VkInstance instance,
    VkDebugUtilsMessengerEXT debugMessenger,
    const VkAllocationCallbacks* pAllocator) {
    auto func = (PFN_vkDestroyDebugUtilsMessengerEXT)vkGetInstanceProcAddr(instance, "vkDestroyDebugUtilsMessengerEXT");
    if (func != nullptr) {
        func(instance, debugMessenger, pAllocator);
    }
}

class HelloTriangleApplication {
public:
    void run() {
        initWindow();
        initVulkan();
        mainLoop();
        cleanup();
    }

private:
    GLFWwindow* window;
    VkInstance instance;
    VkDebugUtilsMessengerEXT debugMessenger;

    void initWindow() {
        glfwInit();

        glfwWindowHint(GLFW_CLIENT_API, GLFW_NO_API);
        glfwWindowHint(GLFW_RESIZABLE, GLFW_FALSE);

        window = glfwCreateWindow(WIDTH, HEIGHT, "Vulkan", nullptr, nullptr);
    }

    void initVulkan() {
        createInstance();
        setupDebugMessenger();
    }

    void mainLoop() {
        while (!glfwWindowShouldClose(window)) {
            glfwPollEvents();
        }
    }

    void cleanup() {
        if (enableValidationLayers) {
            DestroyDebugUtilsMessengerEXT(instance, debugMessenger, nullptr);
        }

        vkDestroyInstance(instance, nullptr);
        glfwDestroyWindow(window);
        glfwTerminate();
    }

    void createInstance() {
        if (enableValidationLayers && !checkValidationLayerSupport()) {
            throw std::runtime_error("validation layers requested, but not available!");
        }

        VkApplicationInfo appInfo = { };
        appInfo.sType = VK_STRUCTURE_TYPE_APPLICATION_INFO;
        appInfo.pApplicationName = "Hello Triangle";
        appInfo.applicationVersion = VK_MAKE_VERSION(1, 0, 0);
        appInfo.pEngineName = "No Engine";
        appInfo.engineVersion = VK_MAKE_VERSION(1, 0, 0);
        appInfo.apiVersion = VK_API_VERSION_1_0;

        VkInstanceCreateInfo createInfo = {};
        createInfo.sType = VK_STRUCTURE_TYPE_INSTANCE_CREATE_INFO;
        createInfo.pApplicationInfo = &appInfo;

        auto extensions = getRequiredExtensions();
        createInfo.enabledExtensionCount = static_cast<uint32_t>(extensions.size());
        createInfo.ppEnabledExtensionNames = extensions.data();
        
        VkDebugUtilsMessengerCreateInfoEXT debugCreateInfo;
        if (enableValidationLayers) {
            createInfo.enabledLayerCount = static_cast<uint32_t>(validationLayers.size());
            createInfo.ppEnabledLayerNames = validationLayers.data();

            populateDebugMessengerCreateInfo(debugCreateInfo);
        } else {
            createInfo.enabledLayerCount = 0;
            createInfo.pNext = nullptr;
        }

        // getExtensionsInfo();

        if (vkCreateInstance(&createInfo, nullptr, &instance) != VK_SUCCESS) {
            throw std::runtime_error("failed to create instance!");
        }
    }

    void populateDebugMessengerCreateInfo(VkDebugUtilsMessengerCreateInfoEXT& createInfo) {
        createInfo = {};
        createInfo.sType = VK_STRUCTURE_TYPE_DEBUG_UTILS_MESSENGER_CREATE_INFO_EXT;
        createInfo.messageSeverity = VK_DEBUG_UTILS_MESSAGE_SEVERITY_VERBOSE_BIT_EXT |
            VK_DEBUG_UTILS_MESSAGE_SEVERITY_WARNING_BIT_EXT |
            VK_DEBUG_UTILS_MESSAGE_SEVERITY_ERROR_BIT_EXT;
        createInfo.messageType = VK_DEBUG_UTILS_MESSAGE_TYPE_GENERAL_BIT_EXT |
            VK_DEBUG_UTILS_MESSAGE_TYPE_VALIDATION_BIT_EXT |
            VK_DEBUG_UTILS_MESSAGE_TYPE_PERFORMANCE_BIT_EXT;
        createInfo.pfnUserCallback = debugCallback;
    }

    void setupDebugMessenger() {
        if (!enableValidationLayers) return;

        VkDebugUtilsMessengerCreateInfoEXT createInfo;
        populateDebugMessengerCreateInfo(createInfo);

        if (CreateDebugUtilsMessengerEXT(instance, &createInfo, nullptr, &debugMessenger) != VK_SUCCESS) {
            throw std::runtime_error("failed to set up debug messenger!");
        }
    }

    std::vector<const char*> getRequiredExtensions() {
        uint32_t glfwExtensionCount = 0;
        const char** glfwExtensions;
        glfwExtensions = glfwGetRequiredInstanceExtensions(&glfwExtensionCount);
        std::vector<const char*> extensions(glfwExtensions, glfwExtensions + glfwExtensionCount);

        if (enableValidationLayers) {
            extensions.push_back(VK_EXT_DEBUG_UTILS_EXTENSION_NAME);
        }

        return extensions;
    }

    bool checkValidationLayerSupport() {
        uint32_t layerCount;
        vkEnumerateInstanceLayerProperties(&layerCount, nullptr);

        std::vector<VkLayerProperties> availableLayers(layerCount);
        vkEnumerateInstanceLayerProperties(&layerCount, availableLayers.data());

        for (const char* layerName : validationLayers) {
            bool layerFound = false;

            for (const auto& layerProperties : availableLayers) {
                if (strcmp(layerName, layerProperties.layerName) == 0) {
                    layerFound = true;
                    break;
                }
            }

            if (!layerFound) {
                return false;
            }
        }

        return true;
    }

    static VKAPI_ATTR VkBool32 VKAPI_CALL debugCallback(
        VkDebugUtilsMessageSeverityFlagBitsEXT messageSeverity,
        VkDebugUtilsMessageTypeFlagsEXT messageType,
        const VkDebugUtilsMessengerCallbackDataEXT* pCallbackData,
        void* pUserData) {
        std::cerr << "validation layer: " << pCallbackData->pMessage << std::endl;

        return VK_FALSE;
    }

    void getExtensionsInfo() {
        uint32_t extensionCount = 0;
        vkEnumerateInstanceExtensionProperties(nullptr, &extensionCount, nullptr);
        std::vector<VkExtensionProperties> extensionsTmp(extensionCount);
        vkEnumerateInstanceExtensionProperties(nullptr, &extensionCount, extensionsTmp.data());

        std::cout << "available extensions:" << std::endl;

        for (const auto& extension : extensionsTmp) {
            std::cout << "\\t" << extension.extensionName << std::endl;
        }
    }
};

int main() {
    HelloTriangleApplication app;

    try {
        app.run();
    } catch (const std::exception& e) {
        std::cerr << e.what() << std::endl;
        return EXIT_FAILURE;
    }

    return EXIT_SUCCESS;
}

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# Vulkan教程