Image views
To use any VkImage, including those in the swap chain, in the render pipeline we have to create a VkImageView object.
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.
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.
First add a class member to store the image views in:
std::vector<VkImageView> swapChainImageViews;Create the createImageViews function and call it right after swap chain creation.
void initVulkan() {
createInstance();
setupDebugMessenger();
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:
void createImageViews() {
swapChainImageViews.resize(swapChainImages.size());
}Next, set up the loop that iterates over all of the swap chain images.
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.
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.
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.
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.
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.
Creating the image view is now a matter of calling vkCreateImageView:
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:
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. In the next chapters we’ll have to set up the graphics pipeline.