Vulkan填坑学习Day04—物理设备与队列

Vulkan 物理设备与队列

Vulkan物理设备与队列 ,通过VkInstance初始化Vulkan后,我们需要在系统中查找并选择一个支持我们所需功能的显卡。实际上,我们可以选择任意数量的显卡并同时使用他们,但在本小节中,我们简单的设定选择规则,即将查找到的第一个图形卡作为我们适合的物理设备。

一、选择物理设备

通过VkInstance初始化Vulkan后,我们需要在系统中查找并选择一个支持我们所需功能的显卡。实际上,我们可以选择任意数量的显卡并同时使用他们,但在本小节中,我们简单的设定选择规则,即将查找到的第一个图形卡作为我们适合的物理设备。
在这里插入图片描述
我们添加函数pickPhysicalDevice并在initVulkan函数中调用。

void initVulkan() {
    createInstance();
    setupDebugCallback();
    pickPhysicalDevice();
}

void pickPhysicalDevice() {
}

最终我们选择的图形显卡存储在类成员VkPhysicalDevice句柄中。当VkInstance销毁时,这个对象将会被隐式销毁,所以我们并不需要在cleanup函数中做任何操作。

VkPhysicalDevice physicalDevice = VK_NULL_HANDLE;

关于获取图形卡列表的方式与获得扩展列表的方式类似。

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

如果Vulkan支持的设备数为0,那么没有任何意义进行下一步,我们选择抛出异常。

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

否则我们分配数组存储所有VkPhysicalDevice的句柄。

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

现在我们需要对它们进行评估,检查它们是否适合我们要执行的操作,因为并不是所有的显卡功能一致。为此我们添加一个新的函数:

bool isDeviceSuitable(VkPhysicalDevice device) {
    return true;
}

我们将检查是否有任何物理设备符合我们的功能需求。

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!");
}

下一步我们介绍isDeviceSuitable函数,并检查第一个需要满足的功能。在后续的小节中,我们将开始使用更多的Vulkan功能,我们会扩展此功能函数以满足更多的检查条件。

二、设备需求检测

评估合适的设备我们可以通过遍历一些细节来完成。基本的设备属性像name, type以及Vulkan版本都可以通过vkGetPhysicalDeviceProperties来遍历得到。

VkPhysicalDeviceProperties deviceProperties;
vkGetPhysicalDeviceProperties(device, &deviceProperties);

可以使用vkGetPhysicalDeviceFeatures查询对纹理压缩,64位浮点数和多视图渲染(VR非常有用)等可选功能的支持:

VkPhysicalDeviceFeatures deviceFeatures;
vkGetPhysicalDeviceFeatures(device, &deviceFeatures);

更多遍历物理设备细节的信息,诸如设备内存、队列簇我们将会在后续小节讨论。

例如,我们假设我们的应用程序仅适用于支持geometry shaders的专用显卡。那么isDeviceSuitable函数将如下所示:

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;
}

为了避免纯粹的单一的判断一个设备是否合适,尤其是当你发现多个设备都合适的条件下,你也可以给每一个设备做权值,选择最高的一个。这样,可以通过给予更高权值获取定制化的图形设备,但如果没有一个可用的设备,可以回滚到集成图形设备。你可以按照如下方式实现:

#include <map>

...

void pickPhysicalDevice() {
    ...

    // Use an ordered map to automatically sort candidates by increasing score
    std::multimap<int, VkPhysicalDevice> candidates;

    for (const auto& device : devices) {
        int score = rateDeviceSuitability(device);
        candidates.insert(std::make_pair(score, device));
    }

    // Check if the best candidate is suitable at all
    if (candidates.rbegin()->first > 0) {
        physicalDevice = candidates.rbegin()->second;
    } else {
        throw std::runtime_error("failed to find a suitable GPU!");
    }
}

int rateDeviceSuitability(VkPhysicalDevice device) {
    ...

    int score = 0;

    // Discrete GPUs have a significant performance advantage
    if (deviceProperties.deviceType == VK_PHYSICAL_DEVICE_TYPE_DISCRETE_GPU) {
        score += 1000;
    }

    // Maximum possible size of textures affects graphics quality
    score += deviceProperties.limits.maxImageDimension2D;

    // Application can't function without geometry shaders
    if (!deviceFeatures.geometryShader) {
        return 0;
    }

    return score;
}

我们不需要在小节内实现所有内容,但我们可以了解如何选择图形设备的过程。当然,我们也可以显示图形设备的名称列表,让用户选择。

因为我们刚刚开始,Vulkan的支持是我们唯一需要的,在这里假设任何GPU都可以:

bool isDeviceSuitable(VkPhysicalDevice device) {
    return true;
}

在下一小节中,我们将会讨论第一个真正需要检查的设备功能。

三、队列族

之前已经简要的介绍过,几乎所有的Vulkan操作,从绘图到上传纹理,都需要将命令提交到队列中。有不同类型的队列来源于不同的队列簇,每个队列簇只允许部分commands。例如,可以有一个队列簇,只允许处理计算commands或者只允许内存传输commands:

我们需要检测设备中支持的队列簇,其中哪一个队列簇支持我们想要的commands。为此我们添加一个新的函数findQueueFamilies来查找我们需要的队列簇。现在我们只会寻找一个支持图形commands队列簇,但是我们可以在稍后的小节中扩展更多的内容。
在这里插入图片描述
此函数返回满足某个属性的队列簇索引。定义结构体,其中索引-1表示”未找到”:

struct QueueFamilyIndices {
    int graphicsFamily = -1;
    bool isComplete() {
        return graphicsFamily >= 0;
    }
};

现在我们实现findQueueFamilies函数:

QueueFamilyIndices findQueueFamilies(VkPhysicalDevice device) {
    QueueFamilyIndices indices;
    ...
    return indices;
}

获取队列簇的列表函数为vkGetPhysicalDeviceQueueFamilyProperties:

uint32_t queueFamilyCount = 0;
vkGetPhysicalDeviceQueueFamilyProperties(device, &queueFamilyCount, nullptr);

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

有关队列簇,结构体VkQueueFamilyProperties包含了具体信息,包括支持的操作类型和基于当前队列簇可以创建的有效队列数。我们至少需要找到一个支持VK_QUEUE_GRAPHICS_BIT的队列簇

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++;
}

现在我们有了比较理想的队列簇查询功能,我们可以在isDeviceSuitable函数中使用,确保物理设备可以处理我们需要的命令:

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

    return indices.isComplete();
}

至此,我们已经找到了我们需要的物理设备,在部分我们会讨论逻辑设备。

附:源代码

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

#include <iostream>
#include <stdexcept>
#include <vector>
#include <cstring>
#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();
//	}
//};

struct QueueFamilyIndices {
	int graphicsFamily = -1;

	bool isComplete() {
		return graphicsFamily >= 0;
	}
};

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);
			createInfo.pNext = (VkDebugUtilsMessengerCreateInfoEXT*)&debugCreateInfo;
		}
		else {
			createInfo.enabledLayerCount = 0;
			createInfo.pNext = nullptr;
		}

		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() {
		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;
	}
};

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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