dxgi: emulate IDXGIOutput::WaitForVBlank() (Wine bug 56799). Unblocks JUCE 7 plugin GUIs.
Applies to Wine 11.19. From https://pr1v8.ca, LGPL-2.1-or-later like Wine.

Subject: [PATCH] dxgi: Emulate IDXGIOutput::WaitForVBlank() from the output
 refresh rate.

JUCE 7 (VSyncThread) and Qt 6.9 drive their repaints from a thread that
loops on IDXGIOutput::WaitForVBlank() and only dispatches deferred
repaints when it returns S_OK. With the E_NOTIMPL stub their windows
paint once and then never update (Wine bug 56799).

Sleep until the next refresh-period boundary of the output's current
display mode, as DXVK does, instead of busy-polling the emulated raster
status.
---
 dlls/dxgi/output.c     | 46 ++++++++++++++++++++++++++++----
 dlls/dxgi/tests/dxgi.c | 59 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 100 insertions(+), 5 deletions(-)

diff --git a/dlls/dxgi/output.c b/dlls/dxgi/output.c
index e828ed0..ef0cf04 100644
--- a/dlls/dxgi/output.c
+++ b/dlls/dxgi/output.c
@@ -17,6 +17,7 @@
  */
 
 #include "dxgi_private.h"
+#include "winternl.h"
 
 WINE_DEFAULT_DEBUG_CHANNEL(dxgi);
 
@@ -363,14 +364,49 @@ static HRESULT STDMETHODCALLTYPE dxgi_output_FindClosestMatchingMode(IDXGIOutput
 
 static HRESULT STDMETHODCALLTYPE dxgi_output_WaitForVBlank(IDXGIOutput6 *iface)
 {
-    static BOOL once = FALSE;
+    struct dxgi_output *output = impl_from_IDXGIOutput6(iface);
+    static LARGE_INTEGER frequency;
+    struct wined3d_display_mode mode;
+    enum wined3d_display_rotation rotation;
+    LARGE_INTEGER now, timeout;
+    unsigned int refresh_rate = 0;
+    ULONGLONG period, next;
+    static BOOL once;
 
+    TRACE("iface %p.\n", iface);
+
+    /* There is no portable way to wait for the real vertical blank here.
+     * Emulate it by sleeping until the next refresh interval boundary of the
+     * output's current display mode, measured on the performance counter, so
+     * that callers which pace their redraws with this call (e.g. JUCE 7's
+     * VSyncThread) keep running instead of spinning on E_NOTIMPL. */
     if (!once++)
-        FIXME("iface %p stub!\n", iface);
-    else
-        TRACE("iface %p stub!\n", iface);
+        FIXME("iface %p, emulating vertical blank from the display mode refresh rate.\n", iface);
 
-    return E_NOTIMPL;
+    wined3d_mutex_lock();
+    if (SUCCEEDED(wined3d_output_get_display_mode(output->wined3d_output, &mode, &rotation)))
+        refresh_rate = mode.refresh_rate;
+    wined3d_mutex_unlock();
+
+    if (refresh_rate < 24 || refresh_rate > 1000)
+        refresh_rate = 60;
+
+    if (!frequency.QuadPart)
+        QueryPerformanceFrequency(&frequency);
+    QueryPerformanceCounter(&now);
+
+    period = frequency.QuadPart / refresh_rate;
+    if (!period)
+        period = 1;
+    next = (now.QuadPart / period + 1) * period;
+
+    /* Relative timeout in 100ns units. */
+    timeout.QuadPart = -(LONGLONG)(((next - now.QuadPart) * 10000000) / frequency.QuadPart);
+    if (!timeout.QuadPart)
+        timeout.QuadPart = -1;
+    NtDelayExecution(FALSE, &timeout);
+
+    return S_OK;
 }
 
 static HRESULT STDMETHODCALLTYPE dxgi_output_TakeOwnership(IDXGIOutput6 *iface, IUnknown *device, BOOL exclusive)
diff --git a/dlls/dxgi/tests/dxgi.c b/dlls/dxgi/tests/dxgi.c
index 59ed17f..80cafa9 100644
--- a/dlls/dxgi/tests/dxgi.c
+++ b/dlls/dxgi/tests/dxgi.c
@@ -5960,6 +5960,64 @@ static void test_maximum_frame_latency(void)
     ok(!refcount, "Device has %lu references left.\n", refcount);
 }
 
+static void test_output_wait_for_vblank(void)
+{
+    LARGE_INTEGER frequency, start, end;
+    DXGI_OUTPUT_DESC output_desc;
+    IDXGIFactory *factory;
+    IDXGIAdapter *adapter;
+    IDXGIOutput *output;
+    double elapsed_ms;
+    DEVMODEW mode;
+    unsigned int i;
+    HRESULT hr;
+
+    hr = CreateDXGIFactory(&IID_IDXGIFactory, (void **)&factory);
+    ok(hr == S_OK, "Got unexpected hr %#lx.\n", hr);
+
+    if (IDXGIFactory_EnumAdapters(factory, 0, &adapter) == DXGI_ERROR_NOT_FOUND)
+    {
+        skip("Adapter not found.\n");
+        IDXGIFactory_Release(factory);
+        return;
+    }
+    if (IDXGIAdapter_EnumOutputs(adapter, 0, &output) == DXGI_ERROR_NOT_FOUND)
+    {
+        skip("Output not found.\n");
+        IDXGIAdapter_Release(adapter);
+        IDXGIFactory_Release(factory);
+        return;
+    }
+
+    hr = IDXGIOutput_GetDesc(output, &output_desc);
+    ok(hr == S_OK, "Got unexpected hr %#lx.\n", hr);
+    memset(&mode, 0, sizeof(mode));
+    mode.dmSize = sizeof(mode);
+    if (!EnumDisplaySettingsW(output_desc.DeviceName, ENUM_CURRENT_SETTINGS, &mode))
+        mode.dmDisplayFrequency = 0;
+
+    QueryPerformanceFrequency(&frequency);
+    QueryPerformanceCounter(&start);
+    for (i = 0; i < 4; ++i)
+    {
+        hr = IDXGIOutput_WaitForVBlank(output);
+        ok(hr == S_OK, "Got unexpected hr %#lx.\n", hr);
+    }
+    QueryPerformanceCounter(&end);
+    elapsed_ms = (end.QuadPart - start.QuadPart) * 1000.0 / frequency.QuadPart;
+
+    /* Four waits span at least three full refresh periods; allow generous
+     * slack for scheduling, and an upper bound to catch a hang. */
+    ok(elapsed_ms < 1000.0, "WaitForVBlank took %.2f ms.\n", elapsed_ms);
+    if (mode.dmDisplayFrequency > 1)
+        ok(elapsed_ms >= 3 * 1000.0 / mode.dmDisplayFrequency * 0.5,
+                "Four waits at %lu Hz took only %.2f ms.\n", mode.dmDisplayFrequency, elapsed_ms);
+
+    IDXGIOutput_Release(output);
+    IDXGIAdapter_Release(adapter);
+    IDXGIFactory_Release(factory);
+}
+
 static void test_output_desc(void)
 {
     IDXGIAdapter *adapter, *adapter2;
@@ -9085,6 +9143,7 @@ START_TEST(dxgi)
     queue_test(test_private_data);
     queue_test(test_maximum_frame_latency);
     queue_test(test_output_desc);
+    queue_test(test_output_wait_for_vblank);
     queue_test(test_object_wrapping);
     queue_test(test_factory_check_feature_support);
     queue_test(test_video_memory_budget_notification);
-- 
2.56.0