Unset qgl_current_fbo when the default FBO is bound

Previously when a new QOpenGLFramebufferObject was bound, the
QOpenGLContextPrivate::qgl_current_fbo member was also updated to point
to this new object.
But if a user called QOpenGLFramebufferObject::bindDefault(),
qgl_current_fbo was not unset, meaning that if the FBO object would be
deleted at some point, qgl_current_fbo would be a dangling pointer.

This patch makes sure to clear the value of qgl_current_fbo when
bindDefault() is called. It is cleared, and not set to point to another
object because the default platform OpenGL FBO is not backed by a
QOpenGLFramebufferObject.

Task-number: QTBUG-56296
Change-Id: I68b53d8b446660accdf5841df3d168ee2f133a90
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

1 files changed, 28 insertions, 0 deletions

diff --git a/tests/auto/gui/qopengl/tst_qopengl.cpp b/tests/auto/gui/qopengl/tst_qopengl.cpp
index e2ad502a52..00b5da92a8 100644
--- a/tests/auto/gui/qopengl/tst_qopengl.cpp
+++ b/tests/auto/gui/qopengl/tst_qopengl.cpp
@@ -114,6 +114,7 @@ private slots:
     void vaoCreate();
     void bufferCreate();
     void bufferMapRange();
+    void defaultQGLCurrentBuffer();
 };
 
 struct SharedResourceTracker
@@ -1525,6 +1526,33 @@ void tst_QOpenGL::bufferMapRange()
     ctx->doneCurrent();
 }
 
+void tst_QOpenGL::defaultQGLCurrentBuffer()
+{
+    QScopedPointer<QSurface> surface(createSurface(QSurface::Window));
+    QScopedPointer<QOpenGLContext> ctx(new QOpenGLContext);
+    ctx->create();
+    ctx->makeCurrent(surface.data());
+
+    // Bind default FBO on the current context, and record what's the current QGL FBO. It should
+    // be Q_NULLPTR because the default platform OpenGL FBO is not backed by a
+    // QOpenGLFramebufferObject.
+    QOpenGLFramebufferObject::bindDefault();
+    QOpenGLFramebufferObject *defaultQFBO = QOpenGLContextPrivate::get(ctx.data())->qgl_current_fbo;
+
+    // Create new FBO, bind it, and see that the QGL FBO points to the newly created FBO.
+    QScopedPointer<QOpenGLFramebufferObject> obj(new QOpenGLFramebufferObject(128, 128));
+    obj->bind();
+    QOpenGLFramebufferObject *customQFBO = QOpenGLContextPrivate::get(ctx.data())->qgl_current_fbo;
+    QVERIFY(defaultQFBO != customQFBO);
+
+    // Bind the default FBO, and check that the QGL FBO points to the original FBO object.
+    QOpenGLFramebufferObject::bindDefault();
+    QOpenGLFramebufferObject *finalQFBO = QOpenGLContextPrivate::get(ctx.data())->qgl_current_fbo;
+    QCOMPARE(defaultQFBO, finalQFBO);
+
+    ctx->doneCurrent();
+}
+
 void tst_QOpenGL::nullTextureInitializtion()
 {
     QScopedPointer<QSurface> surface(createSurface(QSurface::Window));