Merge topic 'qvtk-native-widget-gl-state-fix-release' into release

bfc44285 Silence viewport warnings
a56aed3d Remove direct disable of GL_SCISSOR_TEST

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: David E. DeMarle <dave.demarle@kitware.com>
Merge-request: !4872

GUISupport/Qt/QVTKOpenGLNativeWidget.cxx

@@ -545,8 +545,14 @@ void QVTKOpenGLNativeWidget::paintGL()
 
     f->glBindFramebuffer(GL_READ_FRAMEBUFFER, this->FBO->handle());
     f->glReadBuffer(GL_COLOR_ATTACHMENT0);
+
+    // The viewport state may be modified outside the vtkOpenGLState mechanism, so reset the state here.
+    ostate->ResetGlViewportState();
+
+    // If you get a vtkOpenGLState warning from the call below, you can add
+    // a call to ostate->ResetEnumState(GL_SCISSOR_TEST); to reset the cache state
+    // to whatever the value in OpenGL is.
     ostate->vtkglDisable(GL_SCISSOR_TEST); // Scissor affects glBindFramebuffer.
-    f->glDisable(GL_SCISSOR_TEST); // Scissor affects glBindFramebuffer.
     f->glBlitFramebuffer(0, 0, this->RenderWindow->GetSize()[0], this->RenderWindow->GetSize()[1],
       0, 0, this->RenderWindow->GetSize()[0], this->RenderWindow->GetSize()[1], GL_COLOR_BUFFER_BIT,
       GL_NEAREST);