在gstreamer元素中打开OpenCV窗口

Question

I'm trying to do a very basic Gstreamer element that opens an OpenCV window with an image.

In my element, I have a chain function that only calls the window-opening function called select_points(), which is in select_points.cpp.

the chain_function:

static GstFlowReturn
gst_georeg_chain (GstPad * pad, GstBuffer * buf)
{
  GstGeoreg *filter;

  georeg_val gvals;

  filter = GST_GEOREG (GST_OBJECT_PARENT (pad));

  get_data(&gvals);

  select_points(&gvals);

  return gst_pad_push (filter->srcpad, buf);
}

Now in my select_points.cpp, I have the following code

#include <stdio.h>
#include "datasetup.h"
#include <opencv/cv.h>
#include <opencv/highgui.h>

using namespace cv;

extern "C" void select_points(georeg_val *gvals) //plugin is in C
{
  IplImage* img=0; 
  img=cvLoadImage(gvals->imageName,1);
  if(!img) 
  {
    printf("Could not load image file: \n$%s$\n",gvals->imageName);
  }
  else
  {        
    printf("Image was loaded\n");
    cvNamedWindow("Select", CV_WINDOW_AUTOSIZE); 

    cvMoveWindow("Select", 200, 200); // offset from the UL corner of the screen

    cvShowImage("Select",img);

    cvDestroyWindow("Select");
    cvReleaseImage(&img); 

  }

}

The problem is that when I run the pipeline with my element, it hangs when calling cvNamedWindow. Any suggestions? Everything else works fine if I comment out select_points().

Answer 1

First , move cvNamedWindow() out of select_points() and into the main() function, before the gstreamer pipeline is activated.

Second , if you want to see the window you must add a call to cvWaitKey(0); after cvShowImage() is called. Else, you will end up displaying the image and immediately destroying the window, making it display nothing.

:)