title: Ploting an image with 'imshow' of opencv in webots
body: <p>hi I am using opencv in webots and I want to plot an image . This is the controller: </p>
  
  <pre><code>#include &lt;webots/Robot.hpp&gt;
  #include "opencv2/core/core.hpp"
  #include "opencv2/highgui/highgui.hpp"
  #include "opencv2/imgproc/imgproc.hpp"
  #include &lt;iostream&gt;
  
  using namespace webots;
  using namespace cv;
  
  int main(int argc, char **argv){
  
    Robot *robot = new Robot();
    int timeStep = (int) robot-&gt;getBasicTimeStep();
  
    while (robot-&gt;step(timeStep) != -1) {
        Mat a1 = imread("/home/alireza/Desktop/1.jpg");
        cv::imshow("test",a1);
    };
  
    delete robot;
    return 0;
  }  
  </code></pre>
  
  <p>and this is the makefile:</p>
  
  <pre><code>OPENCV = `pkg-config opencv --cflags --libs` 
  LIBRARIES = $(OPENCV) 
  space :=
  space +=
  WEBOTS_HOME_PATH=$(subst $(space),\ ,$(strip $(subst \,/,$(WEBOTS_HOME))))
  RESOURCES_PATH = $(WEBOTS_HOME)/projects/robots/robotis
  
  CXX_SOURCES = $(wildcard *.cpp)
  include $(WEBOTS_HOME_PATH)/resources/Makefile.include
  </code></pre>
  
  <p>I make it successfully but when I want to run it I face a runtime error about Qt :</p>
  
  <pre><code>[co] qt.qpa.plugin: Could not find the Qt platform plugin "xcb" in ""
  [co] This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.
  </code></pre>
  
  <p>I really need help.</p>