Crafter.Graphics/tests/FrameLoopSync/main.cpp

//SPDX-License-Identifier: LGPL-3.0-only
//SPDX-FileCopyrightText: Copyright (C) 2026 Catcrafts®

// Issue #40: multi-frame-in-flight frame pacing. The renderer used to be
// effectively single-buffered — Render() ended with an unconditional
// vkQueueWaitIdle and shared a single (presentComplete, renderComplete)
// semaphore pair with zero fences for the Window's whole lifetime. This
// reworks the pacing model:
//
//   - one VkFence per in-flight frame slot (a free-running CPU frame counter
//     % numFrames), passed to vkQueueSubmit and waited on before the slot's
//     command buffer is re-recorded — before the acquire, so the slot's
//     acquire semaphore is free again too. Until #160 the fences were keyed
//     by the acquired image index, which tied the frame loop to a swapchain
//     of exactly numFrames images;
//   - one acquire semaphore per frame slot, and one render-complete
//     semaphore per swapchain image (the present holds it until the image
//     comes back), so frame N's render-complete and frame N+1's acquire can
//     be pending at once;
//   - the steady-state vkQueueWaitIdle is gone (kept only on resize /
//     OUT_OF_DATE / teardown).
//
// The fence and semaphore changes are mutually load-bearing: dropping the
// wait-idle while reusing one binary semaphore pair across in-flight frames is
// a textbook Vulkan race, and per-frame semaphores without per-frame fences is
// a command-buffer use-after-free. So this test drives the *real* frame loop —
// a real Wayland surface, a real swapchain, real acquire/submit/present — for
// many more frames than there are in-flight slots, then asserts:
//
//   - every Render() completed and the CPU frame counter advanced by the
//     expected amount (no deadlock on the per-frame fence wait);
//   - the frame slot followed the frame counter, and the acquired image
//     index rotated across more than one image (proof the swapchain is
//     genuinely multi-buffered, not pinned to image 0);
//   - the Vulkan validation layer reported ZERO errors over the whole run.
//     This is the load-bearing check: the old singleton-pair design only
//     avoided being an active race because the wait-idle masked it. Reusing a
//     binary semaphore across overlapping frames, or recording into a command
//     buffer still in flight, both light up the validation layer immediately.
//
// Needs a live Wayland compositor + a Vulkan device at runtime (same as the
// windowed examples), so it shares the native build settings and is Linux-only.

#include "vulkan/vulkan.h"
#include <cstdlib>

import Crafter.Graphics;
import std;

using namespace Crafter;

namespace {

int failures = 0;

void Check(bool ok, std::string_view what) {
    std::println("{}  {}", ok ? "PASS" : "FAIL", what);
    if (!ok) ++failures;
}

} // namespace

int main() {
    Device::Initialize();

    // A real, configured window against the running compositor. Construction
    // performs the xdg configure handshake and creates the swapchain + the
    // per-frame fences/semaphores under test.
    Window window(640, 480, "FrameLoopSync test");

    // Render() with no passes still exercises the full pacing path: per-frame
    // fence wait → acquire (signals the slot's acquire semaphore) → fence
    // reset → barriers → submit (signals the image's render-complete
    // semaphore, fences the command buffer) → present. Run well past
    // numFrames so every semaphore and every per-frame fence is reused
    // several times — exactly the condition the old single-pair / wait-idle
    // design could not survive without draining the queue every frame.
    constexpr int kFrames = 60;
    static_assert(kFrames > Window::numFrames * 3,
                  "must loop enough to reuse each in-flight slot multiple times");

    std::vector<bool> imageSeen(window.images.size());
    bool framesFollowCounter = true;
    for (int i = 0; i < kFrames; ++i) {
        window.Render();
        framesFollowCounter = framesFollowCounter && window.currentFrame == static_cast<std::uint32_t>(i % Window::numFrames);
        if (window.currentImage < imageSeen.size()) {
            imageSeen[window.currentImage] = true;
        }
    }

    // Drain before inspecting — no steady-state wait-idle means GPU work may
    // still be in flight when the loop exits.
    Device::CheckVkResult(vkQueueWaitIdle(Device::queue));

    Check(window.frameCounter == static_cast<std::uint64_t>(kFrames),
          std::format("CPU frame counter advanced once per Render() ({} of {})",
                      window.frameCounter, kFrames));

    Check(framesFollowCounter, "each Render() used frame slot frameCounter % numFrames");

    int distinctImages = 0;
    for (bool seen : imageSeen) if (seen) ++distinctImages;
    Check(distinctImages > 1,
          std::format("swapchain rotated across multiple images ({} of {} images used)",
                      distinctImages, window.images.size()));

    Check(Device::validationErrorCount == 0,
          std::format("no Vulkan validation errors across {} frames ({} seen)",
                      kFrames, Device::validationErrorCount));

    if (failures != 0) {
        std::println("{} check(s) failed", failures);
        return EXIT_FAILURE;
    }
    std::println("all checks passed");
    return EXIT_SUCCESS;
}