Keep track of destroyed QOpenGLContexts in QOpenGLVertexArrayObject

QOpenGLVertexArrayObject saved the QOpenGLContext it was created in at
the point of QOpenGLVertexArrayObjectPrivate::create(), but didn't set
the saved context back to 0 in QOpenGLVertexArrayObjectPrivate::destroy().

The result was that the zero-pointer checks in the VAO destructor never
hit, and we ended up trying to make a destroyed QOpenGLContext current.

This bug was triggered by the QFontEngine having a limit of 4 concurrent
glyph caches, so when we created the fifth glyph cache we would remove
an earlier one, which destroyed its VOA, that referenced a QOpenGLContext
for a window that had been destroyed already.

We now reset the context back to 0, and disconnect aboutToBeDestroyed()
at the point of QOpenGLVertexArrayObjectPrivate::destroy().

Change-Id: Ib16f3877b310144886cf863b16697c137e7c7941
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/src/gui/opengl/qopenglvertexarrayobject.cpp b/src/gui/opengl/qopenglvertexarrayobject.cpp
index b1fd4ffdfe..22ca35a8c3 100644
--- a/src/gui/opengl/qopenglvertexarrayobject.cpp
+++ b/src/gui/opengl/qopenglvertexarrayobject.cpp
@@ -149,8 +149,6 @@ bool QOpenGLVertexArrayObjectPrivate::create()
     }
 
     Q_Q(QOpenGLVertexArrayObject);
-    if (context)
-        QObject::disconnect(context, SIGNAL(aboutToBeDestroyed()), q, SLOT(_q_contextAboutToBeDestroyed()));
 
     QOpenGLContext *ctx = QOpenGLContext::currentContext();
     if (!ctx) {
@@ -202,6 +200,8 @@ void QOpenGLVertexArrayObjectPrivate::destroy()
     if (!vao)
         return;
 
+    Q_Q(QOpenGLVertexArrayObject);
+
     switch (vaoFuncsType) {
 #ifndef QT_OPENGL_ES_2
     case Core_3_2:
@@ -220,6 +220,10 @@ void QOpenGLVertexArrayObjectPrivate::destroy()
         break;
     }
 
+    Q_ASSERT(context);
+    QObject::disconnect(context, SIGNAL(aboutToBeDestroyed()), q, SLOT(_q_contextAboutToBeDestroyed()));
+    context = 0;
+
     vao = 0;
 }