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feat(window): multi-frame-in-flight frame pacing (#40)

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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>
This commit is contained in:
catbot 2026-06-16 15:37:11 +00:00
commit 621016f264
4 changed files with 254 additions and 30 deletions
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31
project.cpp
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@ -264,6 +264,37 @@ extern "C" Configuration CrafterBuildProject(std::span<const std::string_view> a
scrollImpls.emplace_back("tests/MouseScroll/main");
sc.GetInterfacesAndImplementations(ifaces, scrollImpls);
cfg.tests.push_back(std::move(scrollTest));
// Issue #40: multi-frame-in-flight frame pacing (per-image fences
// + per-frame semaphores, no steady-state wait-idle). Drives the
// real frame loop against a live Wayland compositor for many more
// frames than there are in-flight slots and asserts the validation
// layer stays silent — the old singleton-semaphore design only
// avoided being an active race because the wait-idle masked it, so
// a clean multi-frame run is the regression guard. Needs the
// Wayland backend + a real compositor, hence inside the !windows
// block alongside MouseScroll.
Test frameLoopTest;
Configuration& fl = frameLoopTest.config;
fl.path = cfg.path;
fl.name = "FrameLoopSync";
fl.outputName = "FrameLoopSync";
fl.type = ConfigurationType::Executable;
fl.target = cfg.target;
fl.march = cfg.march;
fl.mtune = cfg.mtune;
fl.debug = cfg.debug;
fl.sysroot = cfg.sysroot;
fl.dependencies = cfg.dependencies;
fl.externalDependencies = cfg.externalDependencies;
fl.compileFlags = cfg.compileFlags;
fl.linkFlags = cfg.linkFlags;
fl.defines = cfg.defines;
fl.cFiles = cfg.cFiles;
std::vector<fs::path> frameLoopImpls(impls.begin(), impls.end());
frameLoopImpls.emplace_back("tests/FrameLoopSync/main");
fl.GetInterfacesAndImplementations(ifaces, frameLoopImpls);
cfg.tests.push_back(std::move(frameLoopTest));
}
// Issue #36: BLAS build options. Drives the real hardware AS-build