The renderer was effectively single-buffered despite allocating
triple-buffered infrastructure: Render() ended with an unconditional
vkQueueWaitIdle, and a single (presentComplete, renderComplete)
semaphore pair with zero fences was shared for the Window's lifetime.
Rework the pacing model so up to numFrames frames overlap:
- Per-swapchain-image VkFence, signaled by the submit and waited+reset
before that image's command buffer / descriptor-heap slot is
re-recorded. Keyed by acquired image index (drawCmdBuffers, the heap
slots, and the swapchain images are all image-indexed — see
WriteSwapchainDescriptors). Created signaled so first use passes.
- Per-image render-finished (present) semaphore: the presentation engine
holds it until the image is re-acquired, so per-image is the only safe
key (per-CPU-frame trips VUID-vkQueueSubmit-pSignalSemaphores-00067).
- Per-CPU-frame acquire semaphores (image index unknown until acquire
returns), sized numFrames+1: in-flight depth is bounded by the
per-image fences, so numFrames+1 distinct acquire semaphores guarantee
the reused one has no pending op (VUID-vkAcquireNextImageKHR-01779).
- Drop the steady-state vkQueueWaitIdle; keep it on resize / OUT_OF_DATE
/ teardown.
Add tests/FrameLoopSync: drives the real frame loop against a live
Wayland compositor for 60 frames (>> in-flight slots) and asserts the
CPU frame counter advanced, the swapchain rotated across multiple
images, and the validation layer stayed silent — the load-bearing check,
since the old single-pair design only avoided being an active race
because the wait-idle masked it.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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