To Save OpenGL ViewPort to Image File (glReadPixels, OpenGL->OpenCV)

You can save the Viewport of OpenGL to Image file using glReadPixels function.
And this code is example for saving image file using openCV.
Thank you.

void CaptureViewPort()
{
 
 GLubyte * bits; //RGB bits
 GLint viewport[4]; //current viewport
  
 //get current viewport
 glGetIntegerv(GL_VIEWPORT, viewport);

 int w = viewport[2];
 int h = viewport[3];
 
 bits = new GLubyte[w*3*h];

 //read pixel from frame buffer
 glFinish(); //finish all commands of OpenGL
 glPixelStorei(GL_PACK_ALIGNMENT,1); //or glPixelStorei(GL_PACK_ALIGNMENT,4);
 glPixelStorei(GL_PACK_ROW_LENGTH, 0);
 glPixelStorei(GL_PACK_SKIP_ROWS, 0);
 glPixelStorei(GL_PACK_SKIP_PIXELS, 0);
 glReadPixels(0, 0, w, h, GL_BGR_EXT, GL_UNSIGNED_BYTE, bits);

 IplImage * capImg = cvCreateImage( cvSize(w,h), IPL_DEPTH_8U, 3);
 for(int i=0; i < h; ++i)
 {
  for(int j=0; j < w; ++j)
  {
   capImg->imageData[i*capImg->widthStep + j*3+0] = (unsigned char)(bits[(h-i-1)*3*w + j*3+0]);
   capImg->imageData[i*capImg->widthStep + j*3+1] = (unsigned char)(bits[(h-i-1)*3*w + j*3+1]);
   capImg->imageData[i*capImg->widthStep + j*3+2] = (unsigned char)(bits[(h-i-1)*3*w + j*3+2]);
  }
 }

 cvSaveImage("result.jpg",capImg); 
 cvReleaseImage(&capImg); 
 delete[] bits; 
 
}