fix: DArrowRectangle background color abnormality

Issue: linuxdeepin/developer-center#5187
Bug: https://pms.uniontech.com/bug-view-211649.html

src/widgets/dplatformwindowhandle.cpp

@@ -6,9 +6,27 @@
 
 #include <QWidget>
 #include <QApplication>
+#include <QSurfaceFormat>
+#include <QWindow>
 
 DWIDGET_BEGIN_NAMESPACE
 
+static inline void ensureAlpha(QWidget *w)
+{
+    QWindow *handle = w->windowHandle();
+    if (!handle)
+        return;
+
+    QSurfaceFormat format = handle->requestedFormat();
+    if ((w->windowFlags() & Qt::Window) &&
+            handle->surfaceType() != QSurface::OpenGLSurface
+            && w->testAttribute(Qt::WA_TranslucentBackground)) {
+        format.setAlphaBufferSize(8);
+    }
+
+    handle->setFormat(format);
+}
+
 static QWindow *ensureWindowHandle(QWidget *widget)
 {
     QWidget *window = widget->window();
@@ -27,6 +45,9 @@ static QWindow *ensureWindowHandle(QWidget *widget)
         handle = window->windowHandle();
         window->setAttribute(Qt::WA_NativeWindow, false);
 
+        // FIX developer-center#5187 updateIsTranslucent
+        ensureAlpha(window);
+
         // dxcb version >= 1.1.6
         if (!DPlatformWindowHandle::pluginVersion().isEmpty()) {
             /// TODO: Avoid call parentWidget()->enforceNativeChildren().