Image views
To use any VkImage, including those in the swap chain, in the render pipeline we have to create a VkImageViewobject. An image view is quite literally a view into an image. It describes how to access the image and which part of the image to access, for example if it should be treated as a 2D texture depth texture without any mipmapping levels.
要使用任何VkImage，包括在交换链中的那些，我们必须在渲染管道中创建一个VkImageView对象。一个image视图就是对image 的一个视图。它描述了，如何存取image，存取image 的哪一部分。例如，image应该被视为2D深度纹理，不含mipmap层。
In this chapter we'll write a createImageViews function that creates a basic image view for every image in the swap chain so that we can use them as color targets later on.
本章，我们将写一个createImageViews 函数，它为交换链中的每个image分别创建一个基础的image view，这样，我们就可以将它们当作颜色目标来用了。
First add a class member to store the image views in:
首先，添加成员以保存image view：
std::vector<VkImageView> swapChainImageViews;
Create the createImageViews function and call it right after swap chain creation.
创建createImageViews 函数，在创建交换链后调用它。
void initVulkan() { createInstance(); setupDebugCallback(); createSurface(); pickPhysicalDevice(); createLogicalDevice(); createSwapChain(); createImageViews(); } void createImageViews() { }
The first thing we need to do is resize the list to fit all of the image views we'll be creating:
首先，调整list的大小，以适应我们要创建的image view的数量：
void createImageViews() { swapChainImageViews.resize(swapChainImages.size()); }
Next, set up the loop that iterates over all of the swap chain images.
接下来，在循环中枚举所有的交换链image。
for (size_t i = 0; i < swapChainImages.size(); i++) { }
The parameters for image view creation are specified in a VkImageViewCreateInfo structure. The first few parameters are straightforward.
创建image view的参数由VkImageViewCreateInfo 结构体提供。前几个参数很直观。
VkImageViewCreateInfo createInfo = {}; createInfo.sType = VK_STRUCTURE_TYPE_IMAGE_VIEW_CREATE_INFO; createInfo.image = swapChainImages[i];
The viewType and format fields specify how the image data should be interpreted. The viewType parameter allows you to treat images as 1D textures, 2D textures, 3D textures and cube maps.
字段viewType 和format 标明了image数据应当被如何解释。参数viewType 允许你将image当作1D纹理、2D纹理、3D纹理或cube纹理。
createInfo.viewType = VK_IMAGE_VIEW_TYPE_2D;
createInfo.format = swapChainImageFormat;
The components field allows you to swizzle the color channels around. For example, you can map all of the channels to the red channel for a monochrome texture. You can also map constant values of 0 and 1 to a channel. In our case we'll stick to the default mapping.
字段components 允许你搅和颜色通道。例如，你可以将所有通道都映射到红色通道，实现黑白纹理。你也可以映射0到1的常量到某个通道。在我们的案例中，我们使用默认的映射。
createInfo.components.r = VK_COMPONENT_SWIZZLE_IDENTITY; createInfo.components.g = VK_COMPONENT_SWIZZLE_IDENTITY; createInfo.components.b = VK_COMPONENT_SWIZZLE_IDENTITY; createInfo.components.a = VK_COMPONENT_SWIZZLE_IDENTITY;
The subresourceRange field describes what the image's purpose is and which part of the image should be accessed. Our images will be used as color targets without any mipmapping levels or multiple layers.
字段subresourceRange 描述了image的用途，还有要用image的哪一部分。我们的image要被用作颜色目标，不含mipmap层，不含多个layer。
createInfo.subresourceRange.aspectMask = VK_IMAGE_ASPECT_COLOR_BIT; createInfo.subresourceRange.baseMipLevel = 0; createInfo.subresourceRange.levelCount = 1; createInfo.subresourceRange.baseArrayLayer = 0; createInfo.subresourceRange.layerCount = 1;
If you were working on a stereographic 3D application, then you would create a swap chain with multiple layers. You could then create multiple image views for each image representing the views for the left and right eyes by accessing different layers.
如果你在做一个立体3D应用程序，那么你得创建一个多layer的交换链。然后你就可以为每个image创建多个image view，不同的layer分别代表从左眼和右眼观察。
Creating the image view is now a matter of calling vkCreateImageView:
现在只需调用vkCreateImageView函数来创建image view：
if (vkCreateImageView(device, &createInfo, nullptr, &swapChainImageViews[i]) != VK_SUCCESS) { throw std::runtime_error("failed to create image views!"); }
Unlike images, the image views were explicitly created by us, so we need to add a similar loop to destroy them again at the end of the program:
与image不同，image view是由我们显式地创建的，所以我们需要在程序结束时添加一个相似的循环来销毁它们：
void cleanup() { for (auto imageView : swapChainImageViews) { vkDestroyImageView(device, imageView, nullptr); } ... }
An image view is sufficient to start using an image as a texture, but it's not quite ready to be used as a render target just yet. That requires one more step of indirection, known as a framebuffer. But first we'll have to set up the graphics pipeline.
有了image view就可以将image用作纹理了，但是它还没有准备好被用作渲染目标。那需要下一步的操作，即帧缓存。但是，首先我们必须创建图形管道。