Vulkan教程 - 04 物理設備與隊列族

在通過VkInstance初始化Vulkan後，我們需要選擇物理硬件也就是顯卡來進行後面的工作了，在initVulkan方法中添加一個函數pickPhysicalDevice。我們選擇的顯卡存儲在VkPhysicalDevice中，該對象會在VkInstance銷燬後自動銷燬，所以我們不用在cleanup中做操作。列出顯卡和列出擴展一樣，如下：

uint32_t deviceCount = 0;
vkEnumeratePhysicalDevices(instance, &deviceCount, nullptr);

沒有支持Vulkan的顯卡就退出，否則就可以分配一個數組來存儲VkPhysicalDevice了：

if (deviceCount == 0) {
    throw std::runtime_error("failed to find GPUs with Vulkan support!");
}

std::vector<VkPhysicalDevice> devices(deviceCount);
vkEnumeratePhysicalDevices(instance, &deviceCount, devices.data());

現在需要依次評估，這裏再以引入一個新的函數：

bool isDeviceSuitable(VkPhysicalDevice device) {
    return true;
}

我們會檢查這些物理設備是否有能滿足我們要求的：

for (const auto& device : devices) {
    if (isDeviceSuitable(device)) {
        physicalDevice = device;
        break;
    }
}

if (physicalDevice == VK_NULL_HANDLE) {
    throw std::runtime_error("failed to find a suitable GPU!");
}

然後現在向其添加條件，先查看設備名稱、類型和支持的Vulkan版本：

VkPhysicalDeviceProperties deviceProperties;
vkGetPhysicalDeviceProperties(device, &deviceProperties);

其他特性支持如貼圖壓縮，64位浮點數以及多視口渲染等可以用如下方法查看：

VkPhysicalDeviceFeatures deviceFeatures;
vkGetPhysicalDeviceFeatures(device, &deviceFeatures);

這裏，我們假定需要支持geometry shader，那麼上面這個函數就應該是這樣的：

bool isDeviceSuitable(VkPhysicalDevice device) {
    VkPhysicalDeviceProperties deviceProperties;
    VkPhysicalDeviceFeatures deviceFeatures;
    vkGetPhysicalDeviceProperties(device, &deviceProperties);
    vkGetPhysicalDeviceFeatures(device, &deviceFeatures);
    
    return deviceProperties.deviceType == VK_PHYSICAL_DEVICE_TYPE_DISCRETE_GPU &&
        deviceFeatures.geometryShader;
}

Vulkan幾乎所有的操作，都要將命令提交到隊列中。不同的隊列族有不同的隊列類型，而且每一種隊列族只能執行一組命令。比如，可能有的隊列族只能允許執行內存交換有關的命令。我們需要查看該設備支持哪種類型的隊列族，還要查看哪些隊列族能提供我們想要的功能，所以我們添加一個新的函數：

struct QueueFamilyIndices {
    std::optional<uint32_t> graphicsFamily;

    bool isComplete() {
        return graphicsFamily.has_value();
    }
};

當前我們只是要能支持圖形命令即可，以後會擴展。該方法能返回滿足條件的隊列族的索引。

下面看下隊列族查找方法的實現：

QueueFamilyIndices findQueueFamilies(VkPhysicalDevice device) {
    QueueFamilyIndices indices;
    uint32_t queueFamilyCount = 0;
    vkGetPhysicalDeviceQueueFamilyProperties(device, &queueFamilyCount, nullptr);

    std::vector<VkQueueFamilyProperties> queueFamilies(queueFamilyCount);
    vkGetPhysicalDeviceQueueFamilyProperties(device, &queueFamilyCount, queueFamilies.data());

    int i = 0;
    for (const auto& queueFamily : queueFamilies) {
        if (queueFamily.queueCount > 0 && queueFamily.queueFlags & VK_QUEUE_GRAPHICS_BIT) {
            indices.graphicsFamily = i;
        }

        if (indices.isComplete()) {
            break;
        }

        i++;
    }

    return indices;
}

獲取隊列族列表用vkGetPhysicalDeviceQueueFamilyProperties，VkQueueFamilyProperties包含了一些隊列族的詳細信息，如支持的操作，基於該族能創建的隊列個數等。我們要找到至少一個支持VK_QUEUE_GRAPHICS_BIT的隊列族了，也就是for循環中那一段。現在我們有了這個實現，我們就能在isDeviceSuitable方法中檢查以確定該設備能處理我們需要的命令：

bool isDeviceSuitable(VkPhysicalDevice device) {
    QueueFamilyIndices indices = findQueueFamilies(device);

    return indices.isComplete();
}

最後，完整代碼如下：

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

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

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);
    }
}

struct QueueFamilyIndices {
    std::optional<uint32_t> graphicsFamily;

    bool isComplete() {
        return graphicsFamily.has_value();
    }
};

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

private:
    GLFWwindow* window;
    VkInstance instance;
    VkDebugUtilsMessengerEXT debugMessenger;
    VkPhysicalDevice physicalDevice = VK_NULL_HANDLE;

    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();
        pickPhysicalDevice();
    }

    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!");
        }
    }

    void pickPhysicalDevice() {
        VkPhysicalDevice physicalDevice = VK_NULL_HANDLE;
        uint32_t deviceCount = 0;
        vkEnumeratePhysicalDevices(instance, &deviceCount, nullptr);

        if (deviceCount == 0) {
            throw std::runtime_error("failed to find GPUs with Vulkan support!");
        }

        std::vector<VkPhysicalDevice> devices(deviceCount);
        vkEnumeratePhysicalDevices(instance, &deviceCount, devices.data());

        for (const auto& device : devices) {
            if (isDeviceSuitable(device)) {
                physicalDevice = device;
                break;
            }
        }

        if (physicalDevice == VK_NULL_HANDLE) {
            throw std::runtime_error("failed to find a suitable GPU!");
        }
    }

    bool isDeviceSuitable(VkPhysicalDevice device) {
        QueueFamilyIndices indices = findQueueFamilies(device);

        return indices.isComplete();
    }

    QueueFamilyIndices findQueueFamilies(VkPhysicalDevice device) {
        QueueFamilyIndices indices;
        uint32_t queueFamilyCount = 0;
        vkGetPhysicalDeviceQueueFamilyProperties(device, &queueFamilyCount, nullptr);

        std::vector<VkQueueFamilyProperties> queueFamilies(queueFamilyCount);
        vkGetPhysicalDeviceQueueFamilyProperties(device, &queueFamilyCount, queueFamilies.data());

        int i = 0;
        for (const auto& queueFamily : queueFamilies) {
            if (queueFamily.queueCount > 0 && queueFamily.queueFlags & VK_QUEUE_GRAPHICS_BIT) {
                indices.graphicsFamily = i;
            }

            if (indices.isComplete()) {
                break;
            }

            i++;
        }

        return indices;
    }

    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;
}