Make versioned OpenGL functions working with the subclass pattern

QOpenGLFunctions allows both deriving from it and getting an instance
via QOpenGLContext::functions().

Unsurprisingly a large number of users attempt to use the versioned
function wrappers in the same way. Unfortunately this approach was
not that well supported.

Besides some potential base class exporting issues the real blocker for
QOpenGLWidget - or any versionfunction subclass whose associated context
changes during its lifetime - is that the functions instances could
only be initialized once. Unlike instances retrieved via
QOpenGLContext::versionFunctions(), instances created "manually" were not
deinitialized upon the destruction of the associated context because
context did not know about them.

A pattern like

  initializeOpenGLFunctions();
  delete context;
  create new context and make it current
  initializeOpenGLFunctions();

is working fine in QOpenGLFunctions-derived classes but not with the
versioned ones.

To overcome this, start registering such instances to the context too.
QOpenGLContext::destroy() can then reset the internal state so a
subsequent initializeOpenGLFunctions() will reinitialize properly instead
of bailing out mistakenly thinking that everything is ready to use.

Task-number: QTBUG-45199
Change-Id: Ia1420bcccb33c51508698b7a1b036c7544a66e74
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>

1 files changed, 26 insertions, 0 deletions

diff --git a/src/gui/opengl/qopenglversionfunctions.cpp b/src/gui/opengl/qopenglversionfunctions.cpp
index f3f709c3f0..346a526054 100644
--- a/src/gui/opengl/qopenglversionfunctions.cpp
+++ b/src/gui/opengl/qopenglversionfunctions.cpp
@@ -67,6 +67,17 @@ void QAbstractOpenGLFunctionsPrivate::removeFunctionsBackend(QOpenGLContext *con
     context->removeFunctionsBackend(v);
 }
 
+void QAbstractOpenGLFunctionsPrivate::insertExternalFunctions(QOpenGLContext *context, QAbstractOpenGLFunctions *f)
+{
+    Q_ASSERT(context);
+    context->insertExternalFunctions(f);
+}
+
+void QAbstractOpenGLFunctionsPrivate::removeExternalFunctions(QOpenGLContext *context, QAbstractOpenGLFunctions *f)
+{
+    Q_ASSERT(context);
+    context->removeExternalFunctions(f);
+}
 
 /*!
     \class QAbstractOpenGLFunctions
@@ -182,6 +193,9 @@ QAbstractOpenGLFunctions::QAbstractOpenGLFunctions()
 
 QAbstractOpenGLFunctions::~QAbstractOpenGLFunctions()
 {
+    Q_D(QAbstractOpenGLFunctions);
+    if (d->owningContext)
+        d->removeExternalFunctions(d->owningContext, this);
     delete d_ptr;
 }
 
@@ -191,6 +205,18 @@ bool QAbstractOpenGLFunctions::initializeOpenGLFunctions()
 {
     Q_D(QAbstractOpenGLFunctions);
     d->initialized = true;
+
+    // For a subclass whose instance is not created via
+    // QOpenGLContext::versionFunctions() owningContext is not set. Set it now
+    // and register such instances to the context as external ones. These are
+    // not owned by the context but still need certain cleanup when the context
+    // is destroyed.
+    if (!d->owningContext) {
+        d->owningContext = QOpenGLContext::currentContext();
+        if (d->owningContext)
+            d->insertExternalFunctions(d->owningContext, this);
+    }
+
     return true;
 }