【Vulkan入门】09-CreateFrameBuffer

与网上大多数文章不同，其他文章基本上都使用窗口框架（X11、GLFW、WSL等）提供的surface来显示Vulkan渲染出的图像。我认为那样会屏蔽很多细节，因此我选择使用更原生的方式，即让Vulkan渲染到一块内存中，然后将内存读出再渲染到屏幕上。其实surface只不过是封装好的Image而以。

先叨叨

上一篇创建的RenderPass，但还没有给RenderPass分配内存空间。本篇来介绍如何给RenderPass创建内存空间。RenderPass与内存的对应关系如下图：
在这里插入图片描述
Vulkan的架构设计将RenderPass到Memeory的对应关系拉了一条很长的线路，至于为什么和这么设计的好处，我还理解不到。所以先死记硬背下来。

RenderPass中有很多个Attachment每个，Attachment对应一块内存空间。Attachment用于指明该空间在渲染时具体起到的作用。如：颜色缓存、深度缓存、模板缓存等。
多个Attachment由一个Subpass进行关联，指明一次渲染会用到Subpass中的所有的Attachment。比如将第一个Attachment当作颜色缓存，将第二Attachment当作深度缓存。
一个RenderPass对应一个FrameBuffer。而FrameBuffer中有多个ImageView，每个ImageView对应一个RenderPass中的Attachment。。ImageView还不是真正的内存空间。
ImageView会关联到一个Image。Image是对内存空间的描述，但Image并不是真正的内存空间。
真正的内存空间是Memory，Memory需要从Device上申请，申请完后需要绑定到Image上。

git信息

repository: https://gitee.com/J8_series/easy-car-ui
tag: 09-CreateFrameBuffer
url: https://gitee.com/J8_series/easy-car-ui/tree/09-CreateFrameBuffer

关键代码

VulkanEnv::FindHostVisitbaleMemoryTypeIndex()

上面介绍了Memory需要从Device上申请，而Device可能有多个内存空间（堆）。我希望找到一个GPU和CPU都能访问的堆，因为我想把渲染完的图片拷贝出来。渲染需要GPU访问，而拷贝需要CPU访问。

void VulkanEnv::FindHostVisitbaleMemoryTypeIndex()
{
    VkPhysicalDeviceMemoryProperties pMemoryProperties;
    vkGetPhysicalDeviceMemoryProperties(m_selectedPhysicalDevice, &pMemoryProperties);

    bool found = false;
    for (uint32_t i = 0; i < pMemoryProperties.memoryTypeCount; ++i)
    {
        if (pMemoryProperties.memoryTypes[i].propertyFlags & VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT)
        {
            m_hostVisitbaleMemoryTypeIndex = i;
            found = true;
            break;
        }
    }

    if (false == found)
    {
        throw std::runtime_error("To find host visiable memory is failed");
    }
}

TestPipeLine::CreateFramebuffers()

本方法流程如下：

创建Image
申请Memory
将Image和Memory 绑定到一起
创建ImageView并关联到Image上
创建FrameBuffer。framebufferInfo.pAttachments的值是一个ImageView数组，数组里的元素顺序要与RenderPass中的Attachment顺序一致。Vulkan用这种方式实现了Attachment和ImageView的对应。

    void TestPipeline::CreateFramebuffers()
    {
        //https://registry.khronos.org/vulkan/specs/latest/html/vkspec.html#VkImageCreateInfo
        VkImageCreateInfo imageCreateInfo{};
        imageCreateInfo.sType = VK_STRUCTURE_TYPE_IMAGE_CREATE_INFO;
        imageCreateInfo.pNext = nullptr;
        imageCreateInfo.flags;
        imageCreateInfo.imageType = VK_IMAGE_TYPE_2D;
        imageCreateInfo.format = VK_FORMAT_R8G8B8A8_UINT;
        imageCreateInfo.extent = VkExtent3D{m_width, m_height, 1};
        imageCreateInfo.mipLevels = 1;
        imageCreateInfo.arrayLayers = 1;
        imageCreateInfo.samples = VK_SAMPLE_COUNT_1_BIT;
        imageCreateInfo.tiling = VK_IMAGE_TILING_LINEAR;
        imageCreateInfo.usage = VK_IMAGE_USAGE_STORAGE_BIT | VK_IMAGE_USAGE_COLOR_ATTACHMENT_BIT;
        imageCreateInfo.sharingMode = VK_SHARING_MODE_EXCLUSIVE;
        imageCreateInfo.queueFamilyIndexCount = 0;
        imageCreateInfo.pQueueFamilyIndices = nullptr;
        imageCreateInfo.initialLayout = VK_IMAGE_LAYOUT_UNDEFINED;
        if (VK_SUCCESS != vkCreateImage(m_device, &imageCreateInfo, nullptr, &m_image))
        {
            throw std::runtime_error("To create image is failed!");
        }

        // https://registry.khronos.org/vulkan/specs/latest/html/vkspec.html#VkMemoryAllocateInfo
        VkMemoryAllocateInfo memoryAllocationInfo;
        memoryAllocationInfo.sType = VK_STRUCTURE_TYPE_MEMORY_ALLOCATE_INFO;
        memoryAllocationInfo.pNext = nullptr;
        memoryAllocationInfo.memoryTypeIndex = m_memroyTypeIndex;
        memoryAllocationInfo.allocationSize = m_width * m_height * 4;
        // https://registry.khronos.org/vulkan/specs/latest/html/vkspec.html#vkAllocateMemory
        if (VK_SUCCESS != vkAllocateMemory(m_device, &memoryAllocationInfo, nullptr, &m_imageMemory))
        {
            throw std::runtime_error("To allocate memory is failed!");
        }

        // https://registry.khronos.org/vulkan/specs/latest/html/vkspec.html#vkBindImageMemory
        if (VK_SUCCESS != vkBindImageMemory(m_device, m_image, m_imageMemory, 0))
        {
            throw std::runtime_error("To bind memory is failed!");
        }

        //https://registry.khronos.org/vulkan/specs/latest/html/vkspec.html#VkImageViewCreateInfo
        VkImageViewCreateInfo imageViewCreateInfo{};
        imageViewCreateInfo.sType = VK_STRUCTURE_TYPE_IMAGE_VIEW_CREATE_INFO;
        imageViewCreateInfo.pNext = nullptr;
        imageViewCreateInfo.flags = 0;
        imageViewCreateInfo.image = m_image;
        imageViewCreateInfo.viewType = VK_IMAGE_VIEW_TYPE_2D;
        imageViewCreateInfo.format = VK_FORMAT_R8G8B8A8_UINT;
        imageViewCreateInfo.components.r = VK_COMPONENT_SWIZZLE_IDENTITY;
        imageViewCreateInfo.components.g = VK_COMPONENT_SWIZZLE_IDENTITY;
        imageViewCreateInfo.components.b = VK_COMPONENT_SWIZZLE_IDENTITY;
        imageViewCreateInfo.components.a = VK_COMPONENT_SWIZZLE_IDENTITY;
        imageViewCreateInfo.subresourceRange.aspectMask = VK_IMAGE_ASPECT_COLOR_BIT;
        imageViewCreateInfo.subresourceRange.baseMipLevel = 0;
        imageViewCreateInfo.subresourceRange.levelCount = 1;
        imageViewCreateInfo.subresourceRange.baseArrayLayer = 0;
        imageViewCreateInfo.subresourceRange.layerCount = 1;
        
        if (VK_SUCCESS != vkCreateImageView(m_device, &imageViewCreateInfo, nullptr, &m_imageView))
        {
            throw std::runtime_error("To create image view is failed!");
        }

        VkFramebufferCreateInfo framebufferInfo{};
        framebufferInfo.sType = VK_STRUCTURE_TYPE_FRAMEBUFFER_CREATE_INFO;
        framebufferInfo.renderPass = m_renderPass;
        framebufferInfo.attachmentCount = 1;
        framebufferInfo.pAttachments = &m_imageView;
        framebufferInfo.width = m_width;
        framebufferInfo.height = m_height;
        framebufferInfo.layers = 1;
        //https://registry.khronos.org/vulkan/specs/latest/html/vkspec.html#vkCreateFramebuffer
        if (VK_SUCCESS != vkCreateFramebuffer(m_device, &framebufferInfo, nullptr, &m_framebuffer)) {
                throw std::runtime_error("To create framebuffer is failed!");
        }
    }