Avoid dynamic switching between backingstore composition paths

Make it opt-in because doing a normal backingstore flush does not seem to
work on Cocoa once we use OpenGL on the window. Windows and Linux should
be able to cope with this.

This means that platforms outside Windows and Linux will continue to have
the problem of having GL-based compositing enabled for ever after having a
QOpenGL/QuickWidget shown in the window once, but the issue is most
prevalent on Windows anyway, OS X machines can deal with OpenGL better
in general.

Task-number: QTBUG-49172
Change-Id: I30fd2efa95cc4f6eed9cf7f7613d0750355c775c
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>
Reviewed-by: Paul Olav Tvete <paul.tvete@theqtcompany.com>

2 files changed, 3 insertions, 0 deletions

diff --git a/src/plugins/platforms/windows/qwindowsintegration.cpp b/src/plugins/platforms/windows/qwindowsintegration.cpp
index 6b50ebe8a1..55e6d55e5b 100644
--- a/src/plugins/platforms/windows/qwindowsintegration.cpp
+++ b/src/plugins/platforms/windows/qwindowsintegration.cpp
@@ -282,6 +282,8 @@ bool QWindowsIntegration::hasCapability(QPlatformIntegration::Capability cap) co
         return true;
     case AllGLFunctionsQueryable:
         return true;
+    case SwitchableWidgetComposition:
+        return true;
     default:
         return QPlatformIntegration::hasCapability(cap);
     }
diff --git a/src/plugins/platforms/xcb/qxcbintegration.cpp b/src/plugins/platforms/xcb/qxcbintegration.cpp
index 9cedfa77ad..19e8b1de7d 100644
--- a/src/plugins/platforms/xcb/qxcbintegration.cpp
+++ b/src/plugins/platforms/xcb/qxcbintegration.cpp
@@ -252,6 +252,7 @@ bool QXcbIntegration::hasCapability(QPlatformIntegration::Capability cap) const
     case ForeignWindows: return true;
     case SyncState: return true;
     case RasterGLSurface: return true;
+    case SwitchableWidgetComposition: return true;
     default: return QPlatformIntegration::hasCapability(cap);
     }
 }