made gazebojs tutorials interactive

Author: Hugo Boyer

gazebojs_pubsub/tutorial.md

@@ -22,121 +22,45 @@ Just press enter to get the default values. This operation generates a package.j
 Now you can create javascript files and execute them by invoking node.
 
 
-
-## Publishers
+## Publishers and subscribers
 
 Publishers allow clients and servers to initiate communication, using typed messages. The messages are defined in Gazebo using Protobuf, and they are accessed in javascript via a JSON representation. Publishers can be created in the Gazebo server or the Node client, and messages are sent to unique topics that subscribers can listen to. Messages can be published to existing topics, or new topics can be created for future subscribers.
 
 
-### Code
-Create  publish.js file
-
-    gedit publish.js
+### Node session
 
-And put the following code ([publish.js](https://bitbucket.org/osrf/gazebojs/raw/default/examples/publish.js)):
+Start gazebo
 
-<include src='https://bitbucket.org/osrf/gazebojs/raw/default/examples/publish.js' />
+    gazebo
 
+In a separate terminal, from the gazeboJsPubSub directory, start a node interactive session:
 
-### Code explained
+    node
 
-The first two lines load the Gazebo C++ module into the Node V8 script engine, and an instance of the Gazebo class is created.
+And type in the following two lines to load the Gazebo C++ module into the Node V8 script engine, and crate an instance of the Gazebo class.
 
 ~~~
-var gazebojs = require("gazebojs");
-var gazebo = new gazebojs.Gazebo();
+var gazebojs = require("gazebojs")
+var gazebo = new gazebojs.Gazebo()
 ~~~
 
-The command line arguments are then parsed to determine the type of protobuf Gazebo message to send, an acual instance of a message encoded in JSON, and the topic on which to send the message.
-This information is then used to publish a message:
+Type in the following to publish a message:
 
 ~~~
-gazebo.publish(type, topic , msg);
+gazebo.publish('gazebo.msgs.WorldControl', '~/world_control', { pause: true});
 ~~~
 
-Once published, the message is going to be received by each subscriber for this topic.
-
-
-### Test your publisher:
-
-
-Publish `WorldControl` message on the world_control topic to pause the simulation:
-
-    node publish.js 'gazebo.msgs.WorldControl'  '~/world_control' '{"pause": true}'
-
-You should see the simulation stop in Gazebo, and the following output:
-
-%%%
-type:  [gazebo.msgs.WorldControl]
-topic: [~/world_control]
-msg:   [{ pause: true }]
-
-published!
-bye
-%%%
-
+The arguments to publish are the message type, the topic name, and the message (in JSON format) .  Once published, the message is going to be received by each subscriber for this topic.
 
-## Subscribers
 
 Subscribers provide a callback function for a specific type of message on a certain topic. Each time a new message is published by a publisher, the callback is invoked for every subscriber to this topic.
 
-### Code
-Create subscribe.js file
-
-    gedit subscribe.js
-
-And put the following code ([subscribe.js](https://bitbucket.org/osrf/gazebojs/raw/default/examples/subscribe.js)):
-
-
-<include src='https://bitbucket.org/osrf/gazebojs/raw/default/examples/subscribe.js' />
-
-### Code explained
-
-A subscriber is created by calling subscribe with a message type (the protobuf message name), the topic and a callback function. The call to subscribe is non blocking. The callback has 2 parameters, error and data... following the NodeJs pattern for asynchronous execution.
-In this example, the callback simply converts the JSON to a string and prints it on the console.
+For example, this command displays the world_stats messages by subscribing to the `~/world_stats` topic with the `console.log` message, that prints the messages to the console. You can substitue `console.log` with any function that takes `(error, result)` as arguments.
 
 ~~~
-// subscribe to the topic with a callback function
-gazebo.subscribe(type, topic, function (err, msg){
-    try {
-        if (err) throw(err);
-        console.log('-- [' + count + '] --');
-        count += -1;
-        // convert the Json msg to a string
-        var s= JSON.stringify(msg);
-        console.log(s);
-    } catch(err)  {
-        console.log('error: ' + err);
-        console.log(msg);
-   }
-});
+gazebo.subscribe('gazebo.msgs.WorldStatistics',  '~/world_stats', console.log)
 ~~~
 
-It is possible to unsubscribe to a topic. When unsubscribe is called, all subscriptions to that topic are removed. If you need more than one subscriber on the same topic and you don't want to unsubscribe to them at the same time, you need to use multiple instances of gazebojs.Gazebo.
-
-### Test your subscriber:
-
-
-Subscribe for 5 consecutive `WorldStatistics` messages on the world_stats topic:
-
-    node subscribe.js 'gazebo.msgs.WorldStatistics' '~/world_stats' 5
-
-You should see the following output:
-
-%%%
-subscribing to topic [~/world_stats] of type [gazebo.msgs.WorldStatistics]
-keep the process alive...
--- [5] --
-{"sim_time":{"sec":13081,"nsec":864000000},"iterations":13081864,"paused":false,"pause_time":{"sec":69,"nsec":653000000},"real_time":{"sec":13115,"nsec":231224650}}
--- [4] --
-{"sim_time":{"sec":13082,"nsec":64000000},"iterations":13082064,"paused":false,"pause_time":{"sec":69,"nsec":653000000},"real_time":{"sec":13115,"nsec":431904634}}
--- [3] --
-{"sim_time":{"sec":13082,"nsec":264000000},"iterations":13082264,"paused":false,"pause_time":{"sec":69,"nsec":653000000},"real_time":{"sec":13115,"nsec":632504383}}
--- [2] --
-{"sim_time":{"sec":13082,"nsec":464000000},"iterations":13082464,"paused":false,"pause_time":{"sec":69,"nsec":653000000},"real_time":{"sec":13115,"nsec":833144611}}
--- [1] --
-{"sim_time":{"sec":13082,"nsec":664000000},"iterations":13082664,"paused":false,"pause_time":{"sec":69,"nsec":653000000},"real_time":{"sec":13116,"nsec":33668964}}
-GZPubSub::Unsubscribe() topic = [~/world_stats]
-%%%
+It is possible to unsubscribe to a topic. When `unsubscribe` is called, all subscriptions to that topic are removed.