QT block to plot datapoints as they come in and keep history

[Lukas Haase]

Hello,

I have a block which computes a distance and outputs this distance regularly 
(10x per second) via a message.

I am looking for a way to plot this distance over time: Basically, whenever a 
new update comes in, it should show this value while keeping a certain amount 
of past samples so that the distance can be seen over time.

I played with the QT GUI Time Sink for quite some time (playing with sample 
rate, update period, sending a vector of same numbers in the message or sending 
just a vector with one element). The value updates but it only shows the point 
at t=0 which moves up and down on the y-axis ... but I do not get the history 
over time.

I also tried implementing a "message-to-sample" converter that works like this:

def incoming_msg(self, msg): # whenever new message comes in, update our state
   if pmt.is_f32vector(msg):
      dist = pmt.to_python(msg)
      self.distance = dist[0]

def work(self, input_items, output_items): # this is a source block
    output_items[0][:] = self.distance # for each block, just output constant 
signal
    return len(output_items[0])

Now I see a constant line that shifts up and down regularly, but still no 
distance-vs-time plot.

Any suggestions?

Thanks,
Luke