Calling WPlane::getPose() yields segmentation fault

[dustsigns]

System information (version)

• OpenCV => 3.3
• Operating System / Platform => Ubuntu 16.04 (x86-64)
• Compiler => g++ 5.4.0

Detailed description

Calling WPlane::getPose() before calling showWidget yields a segmentation fault. The following code illustrates the issue:

Steps to reproduce

#include <iostream>
#include <opencv2/viz.hpp>

using namespace std;
using namespace cv;
using namespace cv::viz;

int main()
{
  Viz3d visualization("Test");
  WPlane test_object(Size2d(0, 0));
  const auto pose = test_object.getPose();
  cout << pose.rotation() << endl; //Avoid warning due to unused variable
  visualization.showWidget("Test object", test_object);
  /*visualization.spinOnce(1, true);
  while (!visualization.wasStopped())
    visualization.spinOnce(1, true);*/
  return 0;
}

The program crashes after printing the following error message:

ERROR: In /build/vtk6-YpT4yb/vtk6-6.2.0+dfsg1/Filters/Sources/vtkPlaneSource.cxx, line 104
vtkPlaneSource (0x2348f20): Bad plane coordinate system

ERROR: In /build/vtk6-YpT4yb/vtk6-6.2.0+dfsg1/Common/ExecutionModel/vtkExecutive.cxx, line 784
vtkCompositeDataPipeline (0x2348bb0): Algorithm vtkPlaneSource(0x2348f20) returned failure for request: vtkInformation (0x234a030)
Debug: Off
Modified Time: 311
Reference Count: 1
Registered Events: (none)
Request: REQUEST_DATA
FROM_OUTPUT_PORT: 0
ALGORITHM_AFTER_FORWARD: 1
FORWARD_DIRECTION: 0

According to gdb, the crash happens in the line where Widget::getPose() is called.

The crash also happens when the plane size is (1, 1). In this case, the error message disappears, but the segmentation fault still happens.

[csukuangfj]

The error message is caused by incorrect size, i.e., (0,0).

[csukuangfj]

The crash is caused by referencing null pointer

opencv/modules/viz/src/widget.cpp

Lines 283 to 288 in e2a99d2

	cv::Affine3d cv::viz::Widget3D::getPose() const
	{
	vtkProp3D *actor = vtkProp3D::SafeDownCast(WidgetAccessor::getProp(*this));
	CV_Assert("Widget is not 3D." && actor);
	return Affine3d(*actor->GetUserMatrix()->Element);
	}

actor->GetUserMatrix() is a null pointer if SetUserMatrix is not called previously.