Do not try to eglMakeCurrent for unintended case

1. The QSGThreadedRenderLoop::hide can be called at twice, when the QWindowPrivate::setVisible(false) is called.

• 1.1)

  void QWindowPrivate::setVisible(bool visible)
  {
      //.....
      if (platformWindow)
          platformWindow->setVisible(visible); //QSGThreadedRenderLoop::hide is called 
  
      if (!visible) {
          QHideEvent hideEvent;
          QGuiApplication::sendEvent(q, &hideEvent); //QSGThreadedRenderLoop::hide is called 
      }
  }
  

• 1.2) The backtrace of first QSGThreadedRenderLoop::hide

  (gdb) bt
  #0  QSGThreadedRenderLoop::hide (this=0x557ece1260, window=0x557ec31bb0)
      at /home/alex/disk/Works/yocto/build-ccos/build-pony/workspace/sources/qtdeclarative/src/quick/scenegraph/qsgthreadedrenderloop.cpp:1199
  #1  0x0000007fa1c28c48 in QQuickWindow::event (this=0x557ec31bb0, e=0x7fd749fc90)
      at /home/alex/disk/Works/yocto/build-ccos/build-pony/workspace/sources/qtdeclarative/src/quick/items/qquickwindow.cpp:1744
  #2  0x0000007fa0b82224 in QCoreApplication::notifyInternal2 (receiver=0x557ec31bb0, event=0x7fd749fc90)
      at ../../include/QtCore/5.15.0/QtCore/private/../../../../../../../../../../../workspace/sources/qtbase/src/corelib/thread/qthread_p.h:325
  #3  0x0000007fa0b82454 in QCoreApplication::sendEvent (receiver=<optimized out>, event=event@entry=0x7fd749fc90)
      at /home/alex/disk/Works/yocto/build-ccos/build-pony/workspace/sources/qtbase/src/corelib/kernel/qcoreapplication.cpp:1456
  #4  0x0000007f9c42e65c in QtWaylandClient::QWaylandWindow::reset (this=this@entry=0x557ee6a260, sendDestroyEvent=sendDestroyEvent@entry=true)
      at /home/alex/disk/Works/yocto/build-ccos/build-pony/workspace/sources/qtwayland/src/client/qwaylandwindow.cpp:250
  #5  0x0000007f9c430b78 in QtWaylandClient::QWaylandWindow::setVisible (this=0x557ee6a260, visible=<optimized out>)
      at /home/alex/disk/Works/yocto/build-ccos/build-pony/workspace/sources/qtwayland/src/client/qwaylandwindow.cpp:444
  #6  0x0000007fa1477ba4 in QWindowPrivate::setVisible (this=0x557ecb5000, visible=false)
      at /home/alex/disk/Works/yocto/build-ccos/build-pony/workspace/sources/qtbase/src/gui/kernel/qwindow.cpp:408
  #7  0x0000007fa20be758 in appcommon::WindowBasePrivate::hide (this=0x557ecc8d40) at ../git/impl/src/WindowBasePrivate.cpp:560
  #8  0x0000007fa0b8d208 in QtPrivate::QSlotObjectBase::call (a=0x7fd749fe00, r=0x557ec31350, this=0x557fd3b2c0)
      at ../../include/QtCore/../../../../../../../../workspace/sources/qtbase/src/corelib/kernel/qobjectdefs_impl.h:398
  #9  QMetaObject::invokeMethodImpl (object=0x557ec31350, slot=0x557fd3b2c0, type=Qt::AutoConnection, ret=0x0)
      at /home/alex/disk/Works/yocto/build-ccos/build-pony/workspace/sources/qtbase/src/corelib/kernel/qmetaobject.cpp:1537
  //....
  

2. The QWaylandGLContext::doneCurrent is called by the first QSGRenderThread::invalidateGraphics.

• 2.1) The m_context is not reset in the current following code

  void QWaylandGLContext::doneCurrent()
  {
      eglMakeCurrent(m_eglDisplay, EGL_NO_SURFACE, EGL_NO_SURFACE, EGL_NO_CONTEXT);
  }
  

3 .And then wayland surface is destroyed.

4. After then, the second QSGRenderThread::invalidateGraphics is called, the isValid of QOpenGLContext::makeCurrent do not return the false.

• 4.1) The backtrace of second QSGThreadedRenderLoop::hide

  #0  QSGThreadedRenderLoop::hide (this=0x557ece1260, window=0x557ec31bb0)
      at /home/alex/disk/Works/yocto/build-ccos/build-pony/workspace/sources/qtdeclarative/src/quick/scenegraph/qsgthreadedrenderloop.cpp:1199
  #1  0x0000007fa1477ff8 in QWindow::event (this=this@entry=0x557ec31bb0, ev=ev@entry=0x7fd749fd50)
      at /home/alex/disk/Works/yocto/build-ccos/build-pony/workspace/sources/qtbase/src/gui/kernel/qwindow.cpp:2433
  #2  0x0000007fa1c2898c in QQuickWindow::event (this=0x557ec31bb0, e=0x7fd749fd50)
      at /home/alex/disk/Works/yocto/build-ccos/build-pony/workspace/sources/qtdeclarative/src/quick/items/qquickwindow.cpp:1782
  #3  0x0000007fa0b82224 in QCoreApplication::notifyInternal2 (receiver=0x557ec31bb0, event=0x7fd749fd50)
      at ../../include/QtCore/5.15.0/QtCore/private/../../../../../../../../../../../workspace/sources/qtbase/src/corelib/thread/qthread_p.h:325
  #4  0x0000007fa0b82454 in QCoreApplication::sendEvent (receiver=receiver@entry=0x557ec31bb0, event=event@entry=0x7fd749fd50)
      at /home/alex/disk/Works/yocto/build-ccos/build-pony/workspace/sources/qtbase/src/corelib/kernel/qcoreapplication.cpp:1456
  #5  0x0000007fa1477bc0 in QWindowPrivate::setVisible (this=<optimized out>, visible=false)
      at /home/alex/disk/Works/yocto/build-ccos/build-pony/workspace/sources/qtbase/src/gui/kernel/qwindow.cpp:412
  #6  0x0000007fa20be758 in appcommon::WindowBasePrivate::hide (this=0x557ecc8d40) at ../git/impl/src/WindowBasePrivate.cpp:560
  #7  0x0000007fa0b8d208 in QtPrivate::QSlotObjectBase::call (a=0x7fd749fe00, r=0x557ec31350, this=0x557fd3b2c0)
      at ../../include/QtCore/../../../../../../../../workspace/sources/qtbase/src/corelib/kernel/qobjectdefs_impl.h:398
  #8  QMetaObject::invokeMethodImpl (object=0x557ec31350, slot=0x557fd3b2c0, type=Qt::AutoConnection, ret=0x0)
      at /home/alex/disk/Works/yocto/build-ccos/build-pony/workspace/sources/qtbase/src/corelib/kernel/qmetaobject.cpp:1537
  //...
  

• 4.2) The isValid of QOpenGLContext::makeCurrent do not return the false.

  bool QOpenGLContext::makeCurrent(QSurface *surface)
  {
      Q_D(QOpenGLContext);
      if (!isValid())
          return false;
     ....
  }
  

  bool QWaylandGLContext::isValid() const
  {
      return m_context != EGL_NO_CONTEXT;
  }
  

5. The eglSurface is EGL_NO_SURFACE in the QWaylandGLContext::makeCurrent is called.

6. But our GPU support the EGL_KHR_surfaceless_context, and then the eglMakeCurrent((m_eglDisplay, EGL_NO_SURFACE , EGL_NO_SURFACE , m_context) is not return false.

• So, the QWaylandGLContext::makeCurrent return true. So, the other unnecessary logic is run at this second hide.
• AFAIK, a lot of modern GPU support the EGL_KHR_surfaceless_context.
• Our GPU works weird in this case such as the rendering is not worked after QWindow is shown.
• I guess that this issue is resemble the https://bugs.freedesktop.org/show_bug.cgi?id=96694.

7. To resolve this issue, Do not try to eglMakeCurrent for unintended case.