What is the meaning of 'attachment' when speaking about the Vulkan API?

Question

In relation to the Vulkan API, what does an 'attachment' mean? I see that word used in relation to render passes (i.e.: color attachments). I have vague idea of what I think they are, but would like to hear the definition from an expert.

I'm doing graphics programming for the first time and decided to jump straight into the deep end by starting with Vulkan.

Answer 1

To understand attachments in Vulkan, You first need to understand render-passes and sub-passes.

Render-pass is a general description of steps Your drawing commands are divided into and of resources used during rendering. We can't render anything in Vulkan without a render pass. And each render pass must have one or more steps. These steps are called,

Sub-passes and each sub-pass uses a (sub)collection of resources defined for the render-pass. Render-pass's resources may include render-targets (color, depth/stencil, resolve) and input data (resources that, potentially, were render-targets in previous sub-passes of the same render-pass). And these resources are called,

Attachments (they don't include descriptors/textures/samplers and buffers).

Why don't we call them just render-targets or images? Because we not only render into them (input attachments) and because they are only descriptions (meta data). Images that should be used as attachments inside render-passes are provided through framebuffers.

So, in general, we can call them images, because (as far as I know) only images can be used for attachments. But if we want to be fully correct: images are specific Vulkan resources that can be used for many purposes (descriptors/textures, attachments, staging resources); attachments are descriptions of resources used during rendering.