[PATCH v2 2/2] dwmapi: Simulate DwmFlush blocking behavior.

[Grazvydas Ignotas]

From: Grazvydas Ignotas

The documentation states it's a blocking call. There are reports of it
being used for WaitForVBlank-like purposes [1]. Without blocking Softube
VST plugin logic breaks and they never update their UIs.

[1] https://news.ycombinator.com/item?id=34501612

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=56935
---
 dlls/dwmapi/dwmapi_main.c  | 23 +++++++++++++++++++--
 dlls/dwmapi/tests/dwmapi.c | 41 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 62 insertions(+), 2 deletions(-)

diff --git a/dlls/dwmapi/dwmapi_main.c b/dlls/dwmapi/dwmapi_main.c
index 8d4ccbb1fc4..419216534aa 100644
--- a/dlls/dwmapi/dwmapi_main.c
+++ b/dlls/dwmapi/dwmapi_main.c
@@ -32,6 +32,7 @@

WINE_DEFAULT_DEBUG_CHANNEL(dwmapi);

+static int get_display_frequency(void);

/**********************************************************************
  *           DwmIsCompositionEnabled         (DWMAPI.@)
@@ -88,9 +89,26 @@ HRESULT WINAPI DwmGetColorizationColor(DWORD *colorization, BOOL *opaque_blend)
  */
 HRESULT WINAPI DwmFlush(void)
 {
+    static volatile LONG last_time;
     static BOOL once;
+    DWORD now, interval, last = last_time, target;
+    int freq;

-    if (!once++) FIXME("() stub\n");
+    if (!once++) FIXME("() semi-stub\n");
+
+    // simulate the WaitForVBlank-like blocking behavior
+    freq = get_display_frequency();
+    interval = 1000 / freq;
+    now = GetTickCount();
+    if (now - last < interval)
+        target = last + interval;
+    else
+    {
+        // act as if we were called midway between 2 vsyncs
+        target = now + interval / 2;
+    }
+    Sleep(target - now);
+    InterlockedCompareExchange(&last_time, target, last);

return S_OK;
 }
@@ -262,7 +280,8 @@ static int get_display_frequency(void)
     }
     else
     {
-        WARN("Failed to query display frequency, returning a fallback value.\n");
+        static BOOL once;
+        if (!once++) WARN("Failed to query display frequency, returning a fallback value.\n");
         return 60;
     }
 }
diff --git a/dlls/dwmapi/tests/dwmapi.c b/dlls/dwmapi/tests/dwmapi.c
index a89a1fd705b..20628578f41 100644
--- a/dlls/dwmapi/tests/dwmapi.c
+++ b/dlls/dwmapi/tests/dwmapi.c
@@ -140,9 +140,50 @@ cleanup:
     DestroyWindow(hwnd);
 }

+static void test_DwmFlush(void)
+{
+    LARGE_INTEGER frequency, ts[2];
+    int i, result, ms;
+    DEVMODEA mode;
+    BOOL enabled;
+    HRESULT hr;
+
+    enabled = FALSE;
+    hr = DwmIsCompositionEnabled(&enabled);
+    ok(hr == S_OK, "Got hr %#lx.\n", hr);
+    if (!enabled)
+    {
+        skip("DWM is disabled.\n");
+        return;
+    }
+
+    memset(&mode, 0, sizeof(mode));
+    mode.dmSize = sizeof(mode);
+    result = EnumDisplaySettingsA(NULL, ENUM_CURRENT_SETTINGS, &mode);
+    ok(result, "Failed to get display mode %#lx.\n", GetLastError());
+    ok(mode.dmDisplayFrequency != 0, "dmDisplayFrequency is 0.\n");
+
+    result = QueryPerformanceFrequency(&frequency);
+    ok(result, "Failed to get performance counter frequency.\n");
+
+    result = QueryPerformanceCounter(&ts[0]);
+    ok(result, "Failed to read performance counter.\n");
+    for (i = 0; i < 2; i++)
+    {
+        hr = DwmFlush();
+        ok(hr == S_OK, "Got hr %#lx.\n", hr);
+    }
+    result = QueryPerformanceCounter(&ts[1]);
+    ok(result, "Failed to read performance counter.\n");
+    ms = (ts[1].QuadPart - ts[0].QuadPart) * 1000 / frequency.QuadPart;
+    ok(ms >= 1000 / mode.dmDisplayFrequency,
+        "DwmFlush() took %dms with dmDisplayFrequency %ld.\n", ms, mode.dmDisplayFrequency);
+}
+
 START_TEST(dwmapi)
 {
     test_DwmIsCompositionEnabled();
     test_DwmGetCompositionTimingInfo();
     test_DWMWA_EXTENDED_FRAME_BOUNDS();
+    test_DwmFlush();
 }