Propagate swap interval from QOpenGLWidget to the tlw

Otherwise it is impossible to set a swap interval different
than the one set by QSurfaceFormat::setDefaultFormat().

Both windows and xcb will pick up the updated interval from the
window on the next frame.

Change-Id: I55a59f83a62d3adcea687adf28639646b576ed58
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>

1 files changed, 15 insertions, 1 deletions

diff --git a/src/widgets/kernel/qopenglwidget.cpp b/src/widgets/kernel/qopenglwidget.cpp
index 22ea852d99..2abddd8941 100644
--- a/src/widgets/kernel/qopenglwidget.cpp
+++ b/src/widgets/kernel/qopenglwidget.cpp
@@ -587,7 +587,8 @@ void QOpenGLWidgetPrivate::initialize()
 
     // Get our toplevel's context with which we will share in order to make the
     // texture usable by the underlying window's backingstore.
-    QOpenGLContext *shareContext = get(q->window())->shareContext();
+    QWidget *tlw = q->window();
+    QOpenGLContext *shareContext = get(tlw)->shareContext();
     if (!shareContext) {
         qWarning("QOpenGLWidget: Cannot be used without a context shared with the toplevel.");
         return;
@@ -601,6 +602,19 @@ void QOpenGLWidgetPrivate::initialize()
         return;
     }
 
+    // Propagate settings that make sense only for the tlw.
+    QSurfaceFormat tlwFormat = tlw->windowHandle()->format();
+    if (requestedFormat.swapInterval() != tlwFormat.swapInterval()) {
+        // Most platforms will pick up the changed swap interval on the next
+        // makeCurrent or swapBuffers.
+        tlwFormat.setSwapInterval(requestedFormat.swapInterval());
+        tlw->windowHandle()->setFormat(tlwFormat);
+    }
+    if (requestedFormat.swapBehavior() != tlwFormat.swapBehavior()) {
+        tlwFormat.setSwapBehavior(requestedFormat.swapBehavior());
+        tlw->windowHandle()->setFormat(tlwFormat);
+    }
+
     // The top-level window's surface is not good enough since it causes way too
     // much trouble with regards to the QSurfaceFormat for example. So just like
     // in QQuickWidget, use a dedicated QOffscreenSurface.