Windows QPA: Remove DwmIsCompositionEnabled() usages

According to Microsoft Docs [1], DWM composition is always
enabled and can't be disabled since Windows 8. Now that
we are cleaning up pre-Windows 10 code, this apparently
needs to be removed as well.

[1] https://docs.microsoft.com/en-us/windows/win32/api/dwmapi/nf-dwmapi-dwmiscompositionenabled

Task-number: QTBUG-84432
Change-Id: I64dc049e0741600c8d0ae4db0e9e3bc98a211339
Reviewed-by: André de la Rocha <andre.rocha@qt.io>

1 files changed, 5 insertions, 29 deletions

diff --git a/src/plugins/platforms/windows/qwindowswindow.cpp b/src/plugins/platforms/windows/qwindowswindow.cpp
index a282f7c238..3e291f310d 100644
--- a/src/plugins/platforms/windows/qwindowswindow.cpp
+++ b/src/plugins/platforms/windows/qwindowswindow.cpp
@@ -360,20 +360,11 @@ static inline bool windowIsAccelerated(const QWindow *w)
 
 static bool applyBlurBehindWindow(HWND hwnd)
 {
-    BOOL compositionEnabled;
-    if (DwmIsCompositionEnabled(&compositionEnabled) != S_OK)
-        return false;
-
     DWM_BLURBEHIND blurBehind = {0, 0, nullptr, 0};
 
-    if (compositionEnabled) {
-        blurBehind.dwFlags = DWM_BB_ENABLE | DWM_BB_BLURREGION;
-        blurBehind.fEnable = TRUE;
-        blurBehind.hRgnBlur = CreateRectRgn(0, 0, -1, -1);
-    } else {
-        blurBehind.dwFlags = DWM_BB_ENABLE;
-        blurBehind.fEnable = FALSE;
-    }
+    blurBehind.dwFlags = DWM_BB_ENABLE | DWM_BB_BLURREGION;
+    blurBehind.fEnable = TRUE;
+    blurBehind.hRgnBlur = CreateRectRgn(0, 0, -1, -1);
 
     const bool result = DwmEnableBlurBehindWindow(hwnd, &blurBehind) == S_OK;
 
@@ -2104,12 +2095,6 @@ void QWindowsWindow::releaseDC()
     }
 }
 
-static inline bool dwmIsCompositionEnabled()
-{
-    BOOL dWmCompositionEnabled = FALSE;
-    return SUCCEEDED(DwmIsCompositionEnabled(&dWmCompositionEnabled)) && dWmCompositionEnabled == TRUE;
-}
-
 static inline bool isSoftwareGl()
 {
 #if QT_CONFIG(dynamicgl)
@@ -2133,22 +2118,13 @@ bool QWindowsWindow::handleWmPaint(HWND hwnd, UINT message,
         return false;
     PAINTSTRUCT ps;
 
-    // GL software rendering (QTBUG-58178) and Windows 7/Aero off with some AMD cards
+    // GL software rendering (QTBUG-58178) with some AMD cards
     // (QTBUG-60527) need InvalidateRect() to suppress artifacts while resizing.
-    if (testFlag(OpenGLSurface) && (isSoftwareGl() || !dwmIsCompositionEnabled()))
+    if (testFlag(OpenGLSurface) && isSoftwareGl())
         InvalidateRect(hwnd, nullptr, false);
 
     BeginPaint(hwnd, &ps);
 
-    // Observed painting problems with Aero style disabled (QTBUG-7865).
-    if (Q_UNLIKELY(!dwmIsCompositionEnabled())
-        && ((testFlag(OpenGLSurface) && testFlag(OpenGLDoubleBuffered))
-            || testFlag(VulkanSurface)
-            || testFlag(Direct3DSurface)))
-    {
-        SelectClipRgn(ps.hdc, nullptr);
-    }
-
     // If the a window is obscured by another window (such as a child window)
     // we still need to send isExposed=true, for compatibility.
     // Our tests depend on it.