3 files changed, 28 insertions, 4 deletions
diff --git a/src/gui/kernel/qopenglcontext.cpp b/src/gui/kernel/qopenglcontext.cpp
index 7fc9cceb60..56a3729a4a 100644
--- a/src/gui/kernel/qopenglcontext.cpp
+++ b/src/gui/kernel/qopenglcontext.cpp
@@ -860,15 +860,26 @@ bool QOpenGLContext::hasExtension(const QByteArray &extension) const
 /*!
     Call this to get the default framebuffer object for the current surface.
 
-    On some platforms the default framebuffer object depends on the surface
-    being rendered to, and might be different from 0. Thus, instead of calling
-    glBindFramebuffer(0), you should call
+    On some platforms (for instance, iOS) the default framebuffer object depends
+    on the surface being rendered to, and might be different from 0. Thus,
+    instead of calling glBindFramebuffer(0), you should call
     glBindFramebuffer(ctx->defaultFramebufferObject()) if you want your
     application to work across different Qt platforms.
 
     If you use the glBindFramebuffer() in QOpenGLFunctions you do not have to
     worry about this, as it automatically binds the current context's
     defaultFramebufferObject() when 0 is passed.
+
+    \note Widgets that render via framebuffer objects, like QOpenGLWidget and
+    QQuickWidget, will override the value returned from this function when
+    painting is active, because at that time the correct "default" framebuffer
+    is the widget's associated backing framebuffer, not the platform-specific
+    one belonging to the top-level window's surface. This ensures the expected
+    behavior for this function and other classes relying on it (for example,
+    QOpenGLFramebufferObject::bindDefault() or
+    QOpenGLFramebufferObject::release()).
+
+    \sa QOpenGLFramebufferObject
 */
 GLuint QOpenGLContext::defaultFramebufferObject() const
 {
@@ -879,6 +890,9 @@ GLuint QOpenGLContext::defaultFramebufferObject() const
     if (!d->surface || !d->surface->surfaceHandle())
         return 0;
 
+    if (d->defaultFboRedirect)
+        return d->defaultFboRedirect;
+
     return d->platformGLContext->defaultFramebufferObject(d->surface->surfaceHandle());
 }
 
diff --git a/src/gui/kernel/qopenglcontext_p.h b/src/gui/kernel/qopenglcontext_p.h
index 5004ed6a8e..f9f3ce2c5f 100644
--- a/src/gui/kernel/qopenglcontext_p.h
+++ b/src/gui/kernel/qopenglcontext_p.h
@@ -204,6 +204,7 @@ public:
         , workaround_missingPrecisionQualifiers(false)
         , active_engine(0)
         , qgl_current_fbo_invalid(false)
+        , defaultFboRedirect(0)
     {
         requestedFormat = QSurfaceFormat::defaultFormat();
     }
@@ -242,6 +243,7 @@ public:
     bool qgl_current_fbo_invalid;
 
     QVariant nativeHandle;
+    GLuint defaultFboRedirect;
 
     static QOpenGLContext *setCurrentContext(QOpenGLContext *context);
 
diff --git a/src/widgets/kernel/qopenglwidget.cpp b/src/widgets/kernel/qopenglwidget.cpp
index c6c5e5bc80..d4d23604a3 100644
--- a/src/widgets/kernel/qopenglwidget.cpp
+++ b/src/widgets/kernel/qopenglwidget.cpp
@@ -46,6 +46,7 @@
 #include <QtGui/private/qopenglextensions_p.h>
 #include <QtGui/private/qfont_p.h>
 #include <QtGui/private/qopenglpaintdevice_p.h>
+#include <QtGui/private/qopenglcontext_p.h>
 #include <QtWidgets/private/qwidget_p.h>
 
 QT_BEGIN_NAMESPACE
@@ -792,11 +793,18 @@ void QOpenGLWidgetPrivate::resolveSamples()
 void QOpenGLWidgetPrivate::invokeUserPaint()
 {
     Q_Q(QOpenGLWidget);
-    QOpenGLFunctions *f = QOpenGLContext::currentContext()->functions();
+
+    QOpenGLContext *ctx = QOpenGLContext::currentContext();
+    Q_ASSERT(ctx && fbo);
+
+    QOpenGLFunctions *f = ctx->functions();
+    QOpenGLContextPrivate::get(ctx)->defaultFboRedirect = fbo->handle();
 
     f->glViewport(0, 0, q->width() * q->devicePixelRatio(), q->height() * q->devicePixelRatio());
     q->paintGL();
     flushPending = true;
+
+    QOpenGLContextPrivate::get(ctx)->defaultFboRedirect = 0;
 }
 
 void QOpenGLWidgetPrivate::render()