Vulkan之LogicalDevice

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字数统计: 684 | 阅读时长 ≈ 3

选择完物理设备后，我们实际上很难直接跟物理设备进行交互，一般来说我们都是通过创建逻辑设备来处理。

创建逻辑设备的函数接口如下：

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// Provided by VK_VERSION_1_0
VkResult vkCreateDevice(
    VkPhysicalDevice physicalDevice,
    const VkDeviceCreateInfo* pCreateInfo,
    const VkAllocationCallbacks* pAllocator,
    VkDevice* pDevice);

physicalDevice 是我们的物理设备
pCreateInfo 是指向创建逻辑设备所需要的的结构体的指针
pAllocator 一般为NULL
pDevice 就是我们创建的逻辑设备

下面我们来看一下VkDeviceCreateInfo结构体的内容

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typedef struct VkDeviceCreateInfo {
    VkStructureType                    sType;
    const void*                        pNext;
    VkDeviceCreateFlags                flags;
    uint32_t                           queueCreateInfoCount;
    const VkDeviceQueueCreateInfo*     pQueueCreateInfos;
    uint32_t                           enabledLayerCount;
    const char* const*                 ppEnabledLayerNames;
    uint32_t                           enabledExtensionCount;
    const char* const*                 ppEnabledExtensionNames;
    const VkPhysicalDeviceFeatures*    pEnabledFeatures;
} VkDeviceCreateInfo;

sType—-这个结构体的类型
flag —- 遗留未来用
pNext—- 结构体的扩展指针，一般位NULL，
queueCreateInfoCount — pQueueCreateInfos数组的个数信息
pQueueCreateInfos — 需要创建的对开列的结构信息
enabledLayerCount—-废弃了
ppEnabledLayerNames — 废弃了
enabledExtensionCount — 设备扩展的个数
ppEnabledExtensionNames —设备扩展的名字
pEnabledFeatures — NULL或者是需要激活的一些设备的功能，这个里面内容很，如下所示：

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typedef struct VkPhysicalDeviceFeatures {
    VkBool32    robustBufferAccess;
    VkBool32    fullDrawIndexUint32;
    VkBool32    imageCubeArray;
    VkBool32    independentBlend;
    VkBool32    geometryShader;
    VkBool32    tessellationShader;
    VkBool32    sampleRateShading;
    VkBool32    dualSrcBlend;
    VkBool32    logicOp;
    VkBool32    multiDrawIndirect;
    VkBool32    drawIndirectFirstInstance;
    VkBool32    depthClamp;
    VkBool32    depthBiasClamp;
    VkBool32    fillModeNonSolid;
    VkBool32    depthBounds;
    VkBool32    wideLines;
    VkBool32    largePoints;
    VkBool32    alphaToOne;
    VkBool32    multiViewport;
    VkBool32    samplerAnisotropy;
    VkBool32    textureCompressionETC2;
    VkBool32    textureCompressionASTC_LDR;
    VkBool32    textureCompressionBC;
    VkBool32    occlusionQueryPrecise;
    VkBool32    pipelineStatisticsQuery;
    VkBool32    vertexPipelineStoresAndAtomics;
    VkBool32    fragmentStoresAndAtomics;
    VkBool32    shaderTessellationAndGeometryPointSize;
    VkBool32    shaderImageGatherExtended;
    VkBool32    shaderStorageImageExtendedFormats;
    VkBool32    shaderStorageImageMultisample;
    VkBool32    shaderStorageImageReadWithoutFormat;
    VkBool32    shaderStorageImageWriteWithoutFormat;
    VkBool32    shaderUniformBufferArrayDynamicIndexing;
    VkBool32    shaderSampledImageArrayDynamicIndexing;
    VkBool32    shaderStorageBufferArrayDynamicIndexing;
    VkBool32    shaderStorageImageArrayDynamicIndexing;
    VkBool32    shaderClipDistance;
    VkBool32    shaderCullDistance;
    VkBool32    shaderFloat64;
    VkBool32    shaderInt64;
    VkBool32    shaderInt16;
    VkBool32    shaderResourceResidency;
    VkBool32    shaderResourceMinLod;
    VkBool32    sparseBinding;
    VkBool32    sparseResidencyBuffer;
    VkBool32    sparseResidencyImage2D;
    VkBool32    sparseResidencyImage3D;
    VkBool32    sparseResidency2Samples;
    VkBool32    sparseResidency4Samples;
    VkBool32    sparseResidency8Samples;
    VkBool32    sparseResidency16Samples;
    VkBool32    sparseResidencyAliased;
    VkBool32    variableMultisampleRate;
    VkBool32    inheritedQueries;
} VkPhysicalDeviceFeatures;

而创建队列的结构体如下：

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typedef struct VkDeviceQueueCreateInfo {
    VkStructureType             sType;
    const void*                 pNext;
    VkDeviceQueueCreateFlags    flags;
    uint32_t                    queueFamilyIndex;
    uint32_t                    queueCount;
    const float*                pQueuePriorities;
} VkDeviceQueueCreateInfo;

sType—-这个结构体的类型
flag —- 遗留未来用
pNext—- 结构体的扩展指针，一般位NULL，
queueFamilyIndex — 从物理设备获取到的队列簇的索引
queueCount — 指定索引的队列簇中的队列的个数
pQueuePriorities — 优先级

通过上面的结构体我们就可以创建出逻辑设备了。

然后我们可以通过下面的函数获取队列的句柄：

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// Provided by VK_VERSION_1_0
void vkGetDeviceQueue(
    VkDevice device,
    uint32_t queueFamilyIndex,
    uint32_t queueIndex,
    VkQueue* pQueue);

device — 逻辑设备
queueFamilyIndex — 队列簇索引
queueIndex — 从队列簇中创建的队列的索引，如果创建一个队列，这里就是0。
pQueue — 队列句柄

实际代码如下：

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vkGetDeviceQueue(device, indices.graphicsFamily.value(), 0, &graphicsQueue);
vkGetDeviceQueue(device, indices.presentFamily.value(), 0, &presentQueue);

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