Swapchains other than the main one are VKRSwapchains, owned by the
render manager, each with its own surface, image views, framebuffers
and depth buffer, in the main swapchain's format so the backbuffer render
pass and pipelines work for all of them. A render step with no
framebuffer can name one.
They don't pace the frame: acquiring doesn't wait, and the pass is
skipped if there's no image. The frame's last submit waits on and
signals the semaphores of every swapchain acquired that frame, and each
is presented after the main one. When one goes out of date, it's
recreated at the start of the next frame.
The main swapchain's path is unchanged; frametests on Vulkan match.
VulkanContext::CreateSurface is the old per-platform surface code, now
also used for the extra ones.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
