title: Confused on VK_SUBPASS_EXTERNAL with VkSemaphore
body: <p>I'm reading <a href="https://vulkan-tutorial.com/Drawing_a_triangle/Drawing/Rendering_and_presentation" rel="nofollow noreferrer">Vulkan Tutorial &quot;Rendering and Presentation&quot; chapter</a>, the &quot;Subpass dependencies&quot; section confused me a lot.</p>
  <p>It says: VK_SUBPASS_EXTERNAL is reference to the commands outside the render pass, but, the problem is, there is no commands outside the render pass in that Hello-Triangle example, and I didn't see spec or somewhere says it will automatically create a command block by semaphore, I'm confused now, what does the <code>VK_SUBPASS_EXTERNAL</code> mean if there is no command before render pass?</p>