image_subscriber.cpp

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 * Copyright (c) 2014, Willow Garage, Inc.
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 *
 * image_subscriber.cpp
 *
 *  Created on: Oct 30, 2012
 *      Author: jkammerl
 */

#include "image_subscriber.h"

// Size of image queue -
// a large queue might increase the latency on the video stream
#define IMAGE_BUFFER_SIZE 1

namespace ros_http_video_streamer
{

ImageSubscriber::ImageSubscriber(const std::string& topic, const std::string& transport) :
    topic_(topic),
    transport_(transport),
    nh(""),
    it(nh),
    sub(),
    frame_mutex_(),
    frame_queue_()
{
  if (!topic.empty())
  {
    subscribe();
  }
}

ImageSubscriber::~ImageSubscriber()
{
//  boost::mutex::scoped_lock lock(frame_mutex_);
  sub.reset();
}

void ImageSubscriber::subscribe()
{
  boost::mutex::scoped_lock lock(frame_mutex_);

  sub.reset(new image_transport::SubscriberFilter());
  sub->subscribe(it, topic_, 1, image_transport::TransportHints(transport_));
  sub->registerCallback(boost::bind(&ImageSubscriber::image_cb, this, _1));

  emptyQueue();
}

void ImageSubscriber::emptyQueue()
{
  frame_queue_.clear();
}

void ImageSubscriber::image_cb(const sensor_msgs::ImageConstPtr& msg)
{
  boost::mutex::scoped_lock lock(frame_mutex_);

  sensor_msgs::ImageConstPtr new_msg = sensor_msgs::ImageConstPtr(new const sensor_msgs::Image(*msg));

  frame_queue_.push_front(new_msg);

  while (frame_queue_.size() > IMAGE_BUFFER_SIZE)
    frame_queue_.pop_back();
}

void ImageSubscriber::getImageFromQueue(sensor_msgs::ImageConstPtr& frame)
{
  frame.reset();
  {
    boost::mutex::scoped_lock lock(frame_mutex_);

    // if queue not empty..
    if (frame_queue_.size())
    {
      // pop frame from back of queue
      frame = frame_queue_.back();
      frame_queue_.pop_back();
    }
  }
}

} // ros_http_video_streamer