【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：

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。

1. 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。
2. 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。
3. 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。
4. 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。
5. 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：

1. 创建Image
2. 申请Memory
3. 将Image和Memory 绑定到一起
4. 创建ImageView并关联到Image上
5. 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#VkImageCreateInfoVkImageCreateInfo 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#VkMemoryAllocateInfoVkMemoryAllocateInfo 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#vkAllocateMemoryif (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#vkBindImageMemoryif (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#VkImageViewCreateInfoVkImageViewCreateInfo 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#vkCreateFramebufferif (VK_SUCCESS != vkCreateFramebuffer(m_device, &framebufferInfo, nullptr, &m_framebuffer)) {throw std::runtime_error("To create framebuffer is failed!");}}